By dropping the tank temperature do you not also increase the percentage turn over as you’ll draw more hot water from the tank and mix less cold water. So the increased risk from dropping the temperature is countered by the increased turnover.

It's also worth adding that in the UK the incoming water main (assuming it comes from a regulated supplier) will almost certainly have been treated with small amounts of chlorine to prevent bacterial growth in the supply network. So if you live in a house with modern plumbing (i.e. no redundant dead legs all over the place), and have a combi boiler or unvented cylinder with reasonable daily water turnover, then you are unlikely to have much (if any) legionella bacteria in your system to start with. If you however have a a vented cylinder with a header tank in the loft that has a lid that doesn't fit and old branches of pipework all over the place full that have been capped off and are full of stagnant water, then you might want to bump the temperature up as an extra risk mitigation. Or if you're vulnerable, worried and can afford it, consider getting rid of the header tank. Commercial properties are more likely to have header tanks on both hot and cold supplies, and (from memory, but don't quote me), those are frequently identified to be the source of the contamination.

Thanks for refreshingly clear look at legionella risk. One push-back I've had on same evidence you raised for very low home risk is that a)one cause of pneumonia is legionella, and pneumonia is not uncommon, especially in elderly b)home hw is not tested for legionella, so c)many cases of pneumonia could be home aquired legionella - but no one knows

This video deserves at least 10000000 views !

Solid advice. Storage vessel and pipework materials can also affect the risk of higher levels of legionella. Copper is toxic to the bacteria and as it tends to want to grow on a surface rather than in the body of the water, having copper pipes and hot water cylinders can reduce the growth rate of the bacteria.

Great video, I'm having these conversations daily with customers at the minute!

Absolute legend. I’ve been searching for these answers for a while as we have a water tank with an s plan system, so was concerned using low flow temps on the CH would cause the water tank to become an infested death trap. Very intelligent analysis and pragmatic especially the risk assessment

I have yet to come across a single case of Legionaires disease from an unvented domestic hot water cylinder. Your reasoning is spot on and brilliantly presented with lots of info and clear explanation.

Excellent, helpful and very, very important video. I have learnt so much today in this one video. This should be on a government information programme and circulated to all councils for onward passage to everyone. There is health, safety, cost reduction and environmental guidance in here, and all done in a very listener-friendly style and presentation. Well done and thank you.

In Oz our domestic hot water comes set at 60C. Then there are compulsory tempering valves that come set at about 42C. The hot water cylinders can only be turned down to 50C min approximately. Our big thing in rural areas is tank water storage. Tens of thousands of litres of water just sitting there with minimal to no turnover as we have no mains water. These tanks can be plastic, tin or concrete and the temperature depends on the weather. In Summer we can have a shower straight from the cold tap. You don't need to add any hot water. Never tested to see what these tanks temperature range is but there are an awful lot of people on this system and never heard of any cases of Legionnaires disease. I have always associated it with commercial buildings as you say. Hospitals were always announcing cases. Perhaps that is the point. People get it but it is not diagnosed. You get crook in a Hospital and some test will tell them it is Legionnaires. The rest of us just think we have the Wog. Aussie slang for flu like symptoms.

Seems to be a very sensible approach of balancing the risks; accepting nothing is totally risk free.

Another great video, thanks for helping us to reduce our energy bills. When I moved into my house, I had an old Thorn boiler with copper cylinder and the only control was from a room stat and the boiler stat. The domestic water temperature was usually determined by the boiler output temperature and the boiler had a low output, so it was hard to keep the house warm. Accordingly the domestic water temperature was not particularly high, it was hot, but not uncomfortably, probably 40C. That was the position for 30 years, with no adverse effects on our household of 5. A new system boiler was then installed, with an S plan and a boost in room temperatures was noticed, a nice warm house and really, really hot water. Due to a fault on the boiler, I've had the boiler and hot water tank replaced. The new boiler temp was set at 80C and the cylinder stat at 60C. This caused the water at the tap to be scalding, but at least the house was very warm! I reduced the boiler output to 70C to reduce the domestic hot water temp, but it was still over 63C at the taps. Reducing the cylinder stat to 55C did not really result in a lower temperatures at the tap. It appears the hot water cylinder is heating from the top down, so the top of the tank is at the boiler temperature less any pipe losses and it warms down to the thermostat. I assume that when the water at the thermostat hits 55C it switches the boiler off and there is cycling on the thermostat. I have now reduced the boiler output to 60C to try and cut costs and importantly reduce the domestic hot water temperature. The water at the taps is now at about 57C, so some success, but I doubt that I'll survive the winter months without restoring the boiler to 70C, particularly during the really cold weather. Thankfully your video has given me more confidence to turn the cylinder stat down a little more. Thank you.

This is a very interesting video. As an marine engineer I have experience with potable water, there are a lot of other organisms living in water, so even with treated water you need to be careful about temperature in your hot water cylinder. I noticed after turning down the boiler and the electric thermostat that the hot water had an odour, as I have solar and battery storage I have turned off the gas boiler and use electricity only. I have found that the best temperature is 60c as this stops the smell. The amount of difference in consumption of electricity between 50 and 60 is negligible, I believe this due to us only having showers and have noticed that by having higher hot water we have the temperature on the shower much lower therefore using less hot water.

Wow what an information packed video! 🤯 So helpful and clearly explained! Thanks so much! 🙏🏻😎

Finally what I wanted to check. We are happy at home with temperature set at 45C, but I was doing a manual legionella cycling twice weekly. I'll do eat once in a while now.

Excellent evaluation of risks, especially important when energy savings are needed more than ever.

Finally someone challenging the old wives tale about cranking up the cylinder temp to kill legionella. I was thinking exactly the same when you said how many people actually get legionella from lower water temps. You confirmed my suspicion, I imagine years ago it was some H&S department putting out this theory and now everyone just repeats it without questing if it's correct. Well done thanks for the research! 👍 I did find your hand actions a bit distracting after a while, just like the sign language people on the news 😆. But seriously, thanks for the video.

Really helpful. Thank you for giving clear advice is this area which can induce anxiety in many older people. M

On the heat pump we service, we usually turn legionella off and leave hot water set to constant on (not constant running obvs) and set DHW temps to 40 to 50 degrees depending on the heat pump, cylinder, customer etc.

Adam, yodu nailed it again. I get into red hot arguments with my PH colleagues about resi hot water and they won't accept that 99% of home system already operate at 45 to 55 C. Great to meet you at the H&V awards and well deserved recompense.

Many thanks for this video. Very informative.

Nice to see our thoughts backed up. Been running our hot water at 48c for the last 15 years. GSHP with the legionella cycle running once a month which is the minimum it will do.

I went seeking information about the balance between boiler efficiency and risk of legionella infection. This answered all my questions and I am now running my condensing boiler at 45°C.

Great video, told me exactly what i wanted to know. Thanks.

Great video - i suppose the challenge as a designer is we don't always know our end user! However we should design for flexibility and optimisation because a lot of this is controls based it can be altered.

This channel is gold. Shame most owners don't give a crap about 'the plumber's job'.

Thank you for killing this myth! So many people have told me that you need to have at least 70 degrees in the tank at all times. We have built a woodfired waterheater at home here in Norway, heating it up once a day and the temperature goes between 50 to 80 degrees, saves a ton of electricity

For 30 years our hot water has spent half the year at around 40 or less, but with a high turnover of water it has caused no problems, good to see you 'youngsters' finally cottoning on to this.

love the graphics , keep up with it

Very clear explanation 🙏thank you

Very interesting video and well presented. Intially our water was heated to 60 (unvented cylinder) now turned down to 55. As its heated with a system boiler with basic controls (ideal logic heat 24) this helps our efficiency on the radiator side of things to. More condensing going on I think.

Very informative plus realy interesting.

Even though there's a risk I might die toying with this, I just had to say this content is incredibly well done, particularly in the written form on your website. Thanks! Hope the ad revenue is paying off!

The lawyers must have spent a while pouring over this one!

Great video. If unvented store is set to X degrees, how much hotter would you suggest setting the flow temp of a heat only boiler? For example I set my cylinder stat to 50 degrees and my boiler flow temp to 60, but could I run it at 55c or lower and still have adequate heat transfer through the coil?

since 2016 i have a hybrid solar/electric warm water boiler. since 2017 i´m controlling the electric heating using temperature sensor located in the middle of a 300 liter boiler with small siemens PLC. during less sunny season i keep the temperature up to 50C and then run a legionella cycle of 60C during off hour in the night so each morning the temperature will be maximum. 7..8 months of the year this system is heated mostly using sun , only during winter is mostly electrical. changing this has given more than 30% reduction, in electrical cost 😀

For those larger cylinders with slow turnover you can always fit a de-strat pump to flatten out the temp. variation between top an bottom of the cylinder. a one hour run per day will probably be sufficient.

Great vid as a side note some countries such as Australia required a legonella kill according to the plumbing code at or above 60 deg C at least once per week or 55 Deg C for atleast 6hr per day. On top of this scald protection is required to prevent tap water being above 50 deg C in alot of cases. Over the top if you ask me.

Excellent video! Wonder how UV light would help to safely decrease temperatures.

Very nicely presented and to the point(s) video, thank you. One thing I didn't understand is why a sterilising cycle need only be performed 'after a holiday or once a year'. How fast does the Legionella multiply - do you have any data/rule of thumb on that, relative to tank size and temperature, etc. I'm aiming to take rainwater from the house roof to fill a tank which I can use as a buffer, keeping it heated with water heating solar panels. I will add as many (homemade panels) as is necessary, living in the forest in middle of Sweden. The tank will be outdoors, but super insulated, and of course most likely unused at the coldest times of year when it's minus 23 C -ish at night. If/when I do a sterilising cycle it will be very expensive generally to heat a large volume, so volume is a serious consideration: I do wonder whether it's good then to have a spring and autumn tank, then a much larger summer one, as the solar panel water itself may need to be cooled by the heat exchanger. Cloudy days make a larger usable hot water buffer tank more attractive in general. What I'm wondering is where does the Legionella come from - am I likely to get greater tank infection by using roof water with the risk of bird and squirrel droppings? If so, how fast does it likely breed - will a once weekly sterilising be likely enough, or would one have to worry daily with low volume usage, at say 40C, generally? Can legionella be slowed by other means - carbon dioxide acidifying the water (bacteria doesn't grow in peat bogs, animal carcasses etc last for decades or more in them, and it remains potable for weeks say on a boat), or by adding chlorine or other chemicals periodically, (perhaps measuring the bacteria rate growth of other strains in the water as an indicator of growth, and adding as chemicals as necessary). I know, a lot of factors, a lot of questions, and there's no panacea, but any comments or ideas you may care to reply with would be gratefully received. We are aiming to get off grid eventually, but it's not that easy this far north and indeed I enjoy the challenge and have workshop space and materials to build most things if there are workarounds. Tanks again. (Edit:) does drying of the tank kill Legionella or does it remain dormant waiting to be rehydrated? Can one hang say a sheet of copper in a plastic tank to kill Legionella? I wonder if the fact that most domestic storage boilers/tanks are copper and wonder if that contributes to low domestic infection rates, as opposed to (I assume) steel tanks in industry?

I’ve got a gas combi boiler that heats water on demand, how would I know what my water turnover is and how much of the capacity I’m using?

Great video 👍🏻 quick question…. My boiler has two switch lives, one runs the boiler at 80, the other runs the boiler at whatever the dial it set to. With that being said which is more efficient to heat my 180l unvented cylinder to 45-50 degrees? Run boiler at 80 for a shorter amount of time. Or run my boiler at 50 (same as heating) for a longer amount of time? Thanks.

Great informative content as always. I looked at my water temperature on my Vaillant ecotec plus 837 and have adjusted down to 53 degrees, however I’ve found it overrides this setting and gets as high as 69 degrees according to readout. Any idea what the problem might be………

Very well presented. One question - most modern homes have circulating pumps to have hot water right at the tap - I guess that would help with the "stagnant water" issue? In theory, there should be no stagnant water in the cylinder even if not all of the water is used.

I purchased a new build recently which has a condensing system boiler for heating and hot water and a storage cylinder in the hot press with immersion. I was looking for a way to drop the heating temperature to 45 while keeping the hot water in the cylinder 50-55c. Sadly the boiler doesn’t have separate temperature controls so I can only change both. Would having the immersion on the timer during the night work to ‘boost’ the temperature? I’m not sure what happens when the water in the coil is cooler than the water in the cylinder?

Many thanks for the video. I have a system boiler. If the flow temperature set to 60 and I have cylinder stat temp on the cylinder to 50. Regardless of the flow temperature, the cylinder will stop when it reaches 50? Am i doing anything wrong by setting the flow temp higher ? I have just done this for the radiators to be at a higher temp. I have a vailent ecotec 635. Any advice would be welcome. Thank you.

I have a system with a hot water cylinder and old oil boiler (yes I know but the boiler is only 10 years old so I won't change it yet). As well as setting the hot water to 45°C, I set the hot water to operate for 1 hour per day. I only 'boost' the hot water if it runs cold. That way I prevent the boiler from cycling unecessarily. It makes quite a difference to the running cost but I barely notice when I use the hot water. I just run my shower for a few seconds before getting in, that way the bugs are flushed before I can breath them in.

Been setting cylinder stats for 40 years to 45C. Makes the solar do more work and saves energy. Everyone one wins and no scalding. This clip maybe a sales pitch for ASHP also.🤣

Thanks!

Excellent video with really good scientific data and information about Legionella and most importantly some common sense evaluation of ‘the risk’. I’m a GP and think this puts the often hyped up risk of contracting Legionnaires Disease into a good context. Effectively with only a little precaution as outlined the risks are negligible for domestic hot water. 👏👏

Great info, domestic wise it makes no sense to be heating hot water over 60c. Yes the relative boiling point is higher in pressurised yet all the temperatures on the legionella course only talked about sea level legionella (open vent/gravity systems) rather than how it grows in pressurised. This is due to pressurised systems normally being chlorinated and although at a higher pressure increases boiling point slightly it doesn't increase the bacteria's resilience. The irony is doing the course basically tells you to heat it to 65c regardless. Although the temperatures on this video are correct should be taken into account for the care homes hot water regulations as it's a good rule set to follow. In where assisted bathing is 47c and unassisted is limited to 43c. Generally all new build homes are limited to an average of 46c via TMV at the outlets so there's not much point having the stored water hotter than that unless there's considerable heat loss before it gets to the TMV valves. Sadly as a commercial entity it doesn't matter what type of property we work in it has to be set at 65c because we get pulled up on it during legionella audits. So we just don't write down the information we provide the customer verbally for efficiency sake in domestic settings. Another case of one set of regulations not keeping up with others and new technology.

Scalding and baths: this is where the big risk is (due to immersion and reaction time) and for newbuild Part G requires TMV to limit bathfill to 48 C - this is sensible for any installation but not mandated for existing. Some thermostatic bath fillers can be limited - otherwise use TMV (though avoid both in series)

Excellent stuff. It makes a lot of sense. I have to say though, the hand waving got a bit distracting... One question. My system has a circulating pump running 24x7 on the DHW circuit (the house is long and thin, so without the pump it would take ages for hot water to appear at the end of the run). The water in the pipework then will be cooler then the tank. I think 0 following your presentation - this means I should err a little more on the side of caution and keep the tank a bit hotter. What do you think? My turnover is pretty low too..

Life is funny sometimes. I had a conversation about this very topic the same day that this video was posted. My counterpart in the conversation mentioned that the use of aerators are a problem. His thought was they collect debris and sit at room temperature. His thought was that this is a good environment for the multiplication of the pathogen. Thinking about the intent of an aerator, his theory may hold some water. I did not hear you touch on this and have not heard anyone else talk about it. I did hear you mention flushing out traps to keep them fresh. I would go a step further and say that you should close the lid on the water closet before flushing. ASHRAE did some research on the topic and flushing the toilet makes quite a vapor plume. The state of Illinois has decided to mandate high water temperatures without much input from the plumbing community. Thanks for the informative video.

Thank you for doing this video. It accords with my research too. However there seems to be a real vacuum of data when it comes to domestic properties and legionnaires disease and I wondered if Public Health perceive it as such a low risk they do not set up the necessary data capture mechanisms for dwellings.

Good video, with lots of common sense. I was thinking the other day, if legionella was a major risk in domestic systems we would all be worried about the cold water tanks in the attic (of traditional build houses). The water from the tank is usually directly connected to the cold inlet of the bath mixer tap (which often includes a shower hose) and over the summer months the water must spend many days between 20 C and 45 C, given the ambient loft temperature (which peaked at 45 C in my case) will stay in that range. The tank is insulated to prevent winter freezing, but that just slows down the rate of heat ingress. Its also topped up with chlorinated mains water, but that flow stops when the family goes away on holiday for a week or more. However, as far as I'm aware there is no evidence of an uptick in infection rates afterwards.

Another school day even after over 30 years in the trade 😊

Last few months I've really thought more about the legionnella cycle on the heatpumps we fit. The amount of incidents in domestic homes is stupidly rare and you think of all the homes that have solar thermal (inconsistent heat) and really old header tanks (gravity colds) with no issues from legionnella. Then we install a sealed tank with generally a high turn over, it's near on impossible to get legionnaires. Last samsung we switched it off, due it having solar and an Eddi, which is going to push it over 50 and more on some days of the week.

Really informative. On the stagnant water risk. Often circulation pumps on long lines can result in water being less than 40C [especially if cylinder is at 45C] but continuously moving until it returns to cylinder. Is this a risk already addressed by the fact the water is circulating? Or do additional measures need to be considered?

Good video and analysis. Query, how long do you heat your hot water for per day, what size of tank, and do you use gas or immersion? Also, when is best to take temp of tank, after heating cycle or after main use (post all showers)?

Hi, great video. We are about to move into a new home that has been standing for ages. It looks like it has a combi boiler. What should we do before using the water to be safe and before we can get an engineer in to service it

Great summary of the BIG debate….. BUT most shower thermostatic mixing valves need the hot water at least 10C above the desired mixed temp for the cartridge to work correctly, so 50C is my own base temp and it allows less storage as the lower you go in storage temp, the more hot water you use

Really good and interesting video! One question though: how do you measure or calculate or estimate your daily turnover percentage? You put a lot of focus on that but didn’t explain how you can figure yours out. I have a combi boiler, so does that mean it’s very high almost regardless of how much I use, since there’s no storage beyond what is in the pipes?

I like the way the mitsubishi QUHZ units and thermal stores do it - your "hot water" storage is actually a sealed system and your actual hot water is done instantaneously via a plate heat exchanger (like a combi boiler). As water is heated straight from cold incoming to hot outgoing you can store at whatever temp you want to allow you to get the outlet temp you want. So you could store at 45 to get 40 out with the worries about legionella. Would like to see this implemented with other heat pumps as well

Thank you for this extremely informative video; but please, please, please can you make a short video about possible planned power outages and what average home owners can do, will a small UPS/solar generator keep things running for a few hours at a time, how much power would a heat pump consume in around the same time?

If you have a sealed water cyl, and hot water is mains fed, presumably you only cycle what is in the pipes? The sealed cyl water never contacts the fresh so can Harbour as many bugs as it likes?

It's what I have been saying for years. The amount of energy wasted getting water too hot to then be blended down is huge nationally. I have been running our heat pump cylinder at 45 degrees for 6 years now and I have never run an anti-legionella cycle.

I have a big 150L water tank and there's only me and I barely use any hot water as wash hands in cold water and have a dishwasher and have very quick showers maybe 3x per week. It's quite frustrating paying to keep a tank hot all the time and needing to keep it at a high temp to avoid legionella due to low turnover but there we go. Can't see a way around it in a rental for the moment

Currently I am installing an electric boiler, which will only be heated with excess solar power. The boiler will feed my current (natural gas-fired) heater so I will always have hot water even on cloudy days. Thanks very much for all your information on choosing the right boiler temperature etc. regarding the prevention of legionella! Crazy question: What if I would fill my electric boiler with demineralised water and run an electric pump to circulate the hot water through a plated heat exchanger in a closed circuit? And then run fresh, cold tap water through the other side of the heat exchanger? No tap water would be stored at all, so zero risk on legionella (and no legionella run needed). Optimisations: run the circulation pump only when hot water is demanded (flow detector); and add glycol to the boiler water to increase the heat buffer capacity

Very informative - thank you. But I still have a dilemma. My situation is such we don't need overly how water most of the day. We need hot water in the morning and just luke warm water the rest of the day. I have set a DHW schedule so we heat up to 50 at 6 am and then let it drop to min 35 to boost it up a bit again in the evening (to 40). The water surely goes into the "danger zone" each day for some hours and as we have two elderly I don't want to risk anything. What would be the best safety / economy approach? A weekly anti leginenella cycle or raising the temperatures all together? I guess with present low temperatures setting we do turn around most of the tank. I am thankful for your take on such regime!

Late comment, apologies. If we ignore the legionella considerations for a minute… if a tank is heated to a lower temperature, the user will run down the contents of the tank quicker to achieve the same temperature from the shower/tap. This also means that the boiler has to heat MORE cold water to reach the desired tank temperature. Does this mean the savings are less significant?

Interesting! I got a 170L invented cylinder tank (round 27yrs old) And a new Ideal Vogue Max. Wanted to get OpenTherm and PDHW but not having much luck at moment. All this cos I wanted to have a much lower temp flow for the CH but but but .... Since it's possible to actually lower the cylinder stat boiler to round 50c - does it also means the CH will automatically work in a condensing mode ??? Or does it have to be at 45,c to achieve best performance? We are 2 adults and one little child. I am not sure how much hot water we use from tank. No idea how to calculate the turnover in tank.

I appreciate your content, thanks again. The wife watched your video and she said she could not concentrate on the content because of all the hand movement. :)

So what happens with stratification, when the water in the tank at the level of the thermostat is 55-60C, so the stat has turned off the HW heating, but lower down the tank it’s 30C?

Hi Adam, May I start by saying that I welcome the fact that we are having this level of discussion? To give the personal background, my cylinder stat is set to 60°C, but I actually ignored the stat dial (I find they are generally inaccurate) and measured the water temperature at the cylinder outlet when the thermostat decided it was satisfied, so that's 60°C at the top of cylinder. As the cylinder lagging has been improved by a Heath Robinson extra lagging arrangement, it is only necessary to heat water 3 times a week. This suggests that we are only using 30-40% of the cylinder's capacity on a daily basis. However, the shower is electric so the main way legionella could enter anyone's lungs from the DHW cylinder can be ruled out. I cannot really argue with your approach, and I think people in domestic properties would be generally wise to take your advice. Although I would note that the low number of cases in domestic properties is likely to be partially down to the fact that most people do store their water at a high temperature, because that's how most plumbers set up the cylinders. You mention that pipework and showerheads may contain legionella. I'd love to know if that's really a problem on pipework that is not subject to stagnation. Probably the distributing pipe to my bath is full of it as it's not even used weekly, but the fact is that once you start to run a bath, it's immediately filled with 60°C water means that the contaminated water is likely to represent less than 2% of the content of the bath, so the average bacteria content of the filled bath is still likely to be quite low. Same applies to my electric shower, which, once it has dumped the first pint of water, is running on water that has only been stored for a few seconds. Interesting as this technical discussion is, however, my understanding is that the so-called Water Regulations 1999 insist that stored water be stored at no less than 60°C. Technically, that's the DETR guidance note G18.2 of the blue book, so it's not technically law, but, if the DETR is recommending it, it kind of seems like official "best practice" even if I don't really agree with it. What I'm seeing in Part G is 3.64 which states not a maximum _storage_ temperature of 60°, but a maximum _supply temperature to the distribution system_ of 60°C if the water is normally stored above 80°C so if you can actually direct me to the part of ADG that contradicts what the DETR has said, that would be great.

A neighbour linked his hot water tank (set to 52 degrees heated by heat pump) to his dishwasher as it could take up to 60 degree water. Cheaper to run and higher water turnover.

hi i watch your video's on you tube but i am not a installler etc but intrested all about storage lowloss headers and efficiency etc but there is one question i have not had a video on this is i have a good effecent boiler but i have not found a electrical backup to power my 222f and extra pump and motorsed valves if we have power cuts or interupt supplys can i run it ie is it pure wave ups or invertor and will i damage my 5 year warranty as this year there might be power cuts and i can havd a ups with 33ah battery charged by mains then to a ups or invertor taking out there smaller 7ah battery as ups server unit are all over the place but no batterys can you do a video on what you would need ups or invertor ups mine ups 1.5kw but will i damage the boiler or warranty and i dont want to do that as this is best boiler i have ever had and gas usage etc is great but i dont want to be cold this year if cuts ps iam 67 BUT LEGIONNAIRES NEEDS TO BE ADDRESSED HOT WATER AND SHOWER HEADS LUCKLY MY VIESMANN TANK HAS THIS FACILITY THANKS ALISON

Interestingly "Legionella" doesn't exist as a word. It appears to be a combination of Legionnaires disease & Salmonella disease. At least in the bookish sense. However; each disease is quite different. Both are bacterial infections, though Legionnaires is a respiratory disease & Salmonella is a digestive disease. One is airborne & the other is foodborne. Also; Legionnaires disease is far more common in commercial water (hotels etc) because they use storage tanks rather than heating water according to demand (a domestic combi' boiler). If you visit a hotel in a hot country, always run your shower for a minute & leave the bathroom without breathing. This is because the water in the pipes & shower head is often held stagnant at around 28c.

I've always wondered, how do hot tanks stop the inlet flow from mixing the water up? I used to bug me as a house I lived in, no matter how long you left the immersion heater on the water would go from piping hot to look warm in a quarter of a bath. I was convinced the cold inlet was just mixing the whole tank around.

My issue is the anti legionella cycle that my nest can automatically do will not increase the boiler temperature, I have to manually go to it and turn a dial. Is there any easy way round this? It's a worcester bosch regular boiler.

Looking for some advice here. Am trying to minimise my energy bills with my new Daikin Altherma ASHP and Tank. It's a 210 liter tank and, with only 2 of us in the house, we will have either 2 or 3 showers a day plus use general DHW for washing hands, occasionally a sink of hot-water for non-dishwasher products. I'd estimate our daily usage of DHW to be 120 - 150 liters a day, so approx 60-70% of the tank. We also (as we are EV users) have much cheaper electricity from 2330 to 0530 in the morning (7.5p vs 27.94p /kWh, so nearly a quarter of the price) so the thinking is to put all DHW heating in that time frame. I've slowly brought the DHW setpoint from the installer settings of 60c down to 45c, heating from 0400-0530 on schedule only and this has been fine, this temperature of hot water comfortably lasts us all day, with it maybe once getting ever so slightly not hot enough after a particularly late night tennis match meant a shower at 10pm for me. Whilst I know that, though form a COP standpoint, 4am is probably not the most efficient time of night (as air temperature outside is probably at it's coldest), it actually seems to complete the heatup back to 45c in about 40-50mins (although I do concede it is May at time of writing and I suspect will take longer in winter!), my thinking here is that with my morning shower happening ~8am, it will have had less time to lose heat from the tank than if I did it at 2330-0100) - interested in anyones thoughts/comments on this logic? My main query though, is regarding ALC [disinfection] - I feel totally comfortable with reducing the ALC to 55c as my plan is to do this from 2330hrs once a week; whilst only 90% would die in 20mins, the rest would die in 5-6 hours which would be fine, as we will be asleep whilst that happens. Thoughts/comments from anyone on this logic? HOWEVER, according to the installer, the ASHP won't reach 60 or 55c without use of the booster heater which I'm loathe to use. Plus, having it on even on standby is incredibly noisy and of course it does just have a COP of 1.0 at best - yuck! I've tried turning it off [enjoying the silence instead of this godawful hum and gurgling all the time) and setting disinfect to just 55c and the tank reaches that temperature but the system still reports AH-00 disinfect error, which makes no sense to me. Can anyone help here? As it stands, I am thinking of either manually remembering to turn the booster heater system on once a week on "disinfect night" and suffering the hum all night or maybe installing a timer on that switch? Or do you think I'm totally fine to just let the ASHP get to 55c once a week on the ALC schedule itself and ignoring the AH-00 "error"? thanks for any and all help

Great video and well timed. I've got a traditional system boiler with a hot water tank which has an emersion heater which is not regularly used. I currently have the water temperature set to 50 deg.C (measured), most of the water is turned over every day (my wife and I are 69 and 70 years). My plan is to reduce this to 45 deg.C and setup a reminder to use the emersion heater to bring the temperature up to 60 deg.C every two weeks. Any comments?

Thanks for the information. 70 degrees it is.

If the Cylinder Stat is say set to 45 degree, what level would it be economical to run the Boiler HW at ? Note Boiler HW is currently set at 80 and has Domestic HW Priority, and CH is set to 60.

Does using a heat battery for water heating at mains pressure loose less heat in the store than a unvented cylinder heated by an ashp if you have baths although i assume the ultimate is heating the heat battery with an ashp at 65 degrees Thanks

My thermo only controls the heat pump for radiators have a log burner with boiler.

I have a combi. I set it to 42*C as that gives me a nice full open hot tap shower. For everything else, there is bleach or bleach containing spray.

In Germany they use something called like a ‘freshwater module' and do you have any experience with that?

My Vaillant Ecotec Pro 28 has DHW set to 40° but if I check the boiler while hot water is running I see it reaching up to 63° 🤔

I have a hot water tank and a single temp control on the front of my boiler. If I set thermostat on the hot water tank to 45 what do you recommend as the minimum flow temp on the boiler to make sure it doesn’t take an age to top up the hot water?

How do I find out how much hot water I'm using? We're a youngish family of four, but all told we probably take about 8 showers (pretty short with water off while we soap up) over a week and wash at the sink the rest of the time so I'm thinking that we'll be lucky to use much more than 100l of our 250l tank (40%) a day? Presumably there's no chance of me turning the temperature down below 65 on our unvented system boiler to allow for 53 degrees plus to cater for such a low turnover?

A QUESTION for you (couldn't see the answer in the comments nor online). The grahic showing the Risk of TEMPERATURE vs TURNOVER. In X-axis : what is the "unit"? It looks like it could be number of volume change-over per year? As for me, I leave my boiler OFF from March to November and let the 30 solar hot water tube and 250 litre tank do the work (100% hot water for 8 month!). Then in the winter, I press "1 hour" timer 2 or 3 times a week when the water gets cold to reheat with gas. so by gas bill is £120/yr with near passive house refurb. I have Raychem hot water pipework trace heating cable set at 50°C with Kingspan Kooltherm pipe insulation around it so I always have water at 50°C within 3 seconds. If the tank is at 30°C, I don't realise until 2 minutes later!

I knocked my combi boiler down to 40 deg cel recently. As used everyday the pipes should be clear of any buildup ever occurring.

Any saving we make on storing at 45c seems to be lost when the ALC does it's thing each week (ASHP) vaillant heats the water to 75c I'm thinking to turn the ALC off now.

You very briefly mentioned the downside of reducing HW tank temp. The volume won't last so far as there is less blending required with cold water to get to a comfortable outlet temp. Ensure spray head taps and shower heads to let the tank last longer. Also no mention of the third requirement of Leg. growth - a food source. Ensure CW tanks have a cover and clean them out if the bottom can't be seen.

I’ve converted my combi to run a 300l unvented tank. The boiler has no option to high fire when heating the tank I had planned to use the immersion once a week to boost to 60c so I could maintain optimal heating flow and return. I’ve just set my Evo home to 50 (May go less) and I’ll boost once a month possibly. I have 4 kids 5 and under so high water use.

I turned mine down recently so the temp comes out perfect for the kids baths. If we need to wash things up that can't go in the dishwasher, we just boil a bit of water. Painful to think how much money I've wasted in the past by not tuning it properly.

Temperature stratification is insane, and much worse than you think. My tank will reach steady-state equilibrium with a 55C setpoint, but the bottom remains in the 23-25C range. It will not naturally equalize. I had to install a small mixing pump from hot outlet to cold inlet. My tank is quite large and made for solar installations. I had to install a 1100 watt heating element at about the 1/3 height mark. So there's about 400mm of water below the heating element. I can measure the temperature of the hot water tank at any point along its height by testing the outlets, of which there are many. The temperature stratification is wild. If left for a week with absolutely no water usage the bottom of that tank will stabilize between 23-25C, even if the rest of the tank is holding steady at 55C. The temperature drops off very quickly below the heating element. I would have bet that convection or conduction would mix the tank somewhat, but nope. It blew my mind.

Ours has been set to 45C for decades. Never understood why cylinder stats went above 50.

In college we had a steam tower for us to learn on.. it had the bug , only found out until someone got sick