Not sure how you find the time to produce such informative videos but yet again another brilliant presentation, learning so much from them. Mega Thanks.

Fantastic content Derek! You make it very interesting and have a great way of teaching without mind clogging jargon . About time we got our heads around this as fitters. Looking forward to the weather comp video . Cheers

Enjoyed this , much of this is something I've often spoken about, trying to explain to customers that they would be better having a smaller combination boiler than the 37kw recommend by a competitor.. thanks for your efforts,I'll use this video for future reference for customers.. Great stuff thanks for your efforts 👍😊

Wow I learned so much from your vid many thanks! Got some good questions to ask the companies quoting for my boiler replacement!

Food for thought Derek... great stuff cheers pal.

Good advice, I've used the service menu on my Greenstar CDi 30 to set Max. output (heating) to be 50%. Also set the HW temp so I only need a tiny amount of cold water mixed in the shower. I always use a dishwasher so don't need piping hot water for doing dishes.

Great video. I am in the US and while I had to do some conversions on the numbers by and large the same principles exist here. I could tell my new boiler (Dunkirk - not sure if you have those over there) was way over powered for my home when it was only cycling on for 2 to 3 minutes at a time. I reduced the target temp and high limit to 160 F and the system cycles much more reasonably now (fires on for 10-12 minutes and only cycles about twice an hour).

Very interesting video..Thank you Derek

The problem for customers, who have had a boiler 'mis-installed/poorly commisioned', is that to call out an engineer to range rate the boiler, it will cost you £150 just to get them through the door, thus negating a couple of years savings. The 80% of 80% of 80% should now be suing their installers for not doing the job properly in the first place. On another note, great content, presented well and ultimately illuminating. Quick question....after range rating a WB system 30KW CDI, (all button controlled) must you then re run a telegan flue analysis?

Derek, your a genius mate

Great Video very few engineers understand about rating boilers for different homes.

Brilliant rebound, on commissioning a boiler I do hot water then heating, on a service I just do high and low.

Good educational video , Thanks

Great video thanks. I'm considering adding a smart thermostat to my home which do weather compensation via the internet, do you think that is a good approach or should I hardwire a dedicated outdoor sensor?

I along with many others have suddenly started to take an interest in the white box in the corner, so these videos are very useful. The only problem I have is a 30kW boiler that is only six years old. If I had taken the trouble to investigate this type of information before it was fitted, I would have gone for a smaller, cheaper boiler. Marketing is a very powerful tool. Look forward to the video regarding weather compensation.

I’ve just an Ideal vogue system boiler installed with hot water priority and weather comp. The boiler runs mostly around 45 to 50 deg flow and 38 to 45 return on heating so is always in condensing mode. With hot water it’s heating at 80 deg, but that’s only for 40 mins a day in total

I'm using a Tado which I believe includes weather compensation . Do you think I should still Install an external weather compensator.

How can i do my calcs? I have 16 rads, 3 of which are towel rails, 11 are double rads and 1 single. I have an 835 Vailant Combi. Modern home, good insulation etc, i also run underfloor heating off the boiler in one 20sqm room. What should i rate the boiler down to please?

hi can you please supply a link to your explanation on heat only boilers ie range rating .thanks

Great video. Quick question can you do the same on a storage combi because there is some storage so you need to maintain a higher water temp because of legionaires disease?

Very interesting video Derek. Only thing I would add is, even if you get the return temp down to 54 how much gas are you saving, 4% at best, but probably 3 or even 2%. So between £20 and £40 per year on a £1000 gas bill. Seems pointless to me.

Thank you. Couldn't some of the discrepancy between the boiler set water temp and the actual temp coming out of the tap depend on the accuracy of the temperature sensor and thermostat in the boiler?

If my taps allow way too much flow, then, would it help if I restricted the water supply to the boiler? Just a thought.

I am replacing Brittony 11T somewhat reluctantly as simple tends to be best! we heat with balanced flue wallheaters 40 years old! Cost of pilot a significant cost with current gas costs .The Rinnai powered flue spark ignition my choice. Condensing or non condensing? Condensing more efficient,costs more. non condensing cost less less efficient whichis the best choice?

I have always wondered why my Vaillant combi condensing boiler still 'plumes' even with the flow temperature is only 50c. Surely all the water vapour should condense and flue gas should be invisible?

Will be very interested in your forthcoming video regarding system boilers. This is what I have in my house (Vaillant EcoTec Plus 630), a 230L Megaflo and a 'full' tado installation including eTRVs on every radiator (along with separate schedules for each room and set points of 19C). The one big challenge is that tado does not have functionality to modulate the flow temperature depending on the call for heat (hot water / heating) so I am forced to have a set point of 60C for water and heating so as to remove the risk of legionaires in the water tank. Would appreciate your thoughts on how to maximise the efficiency of the overall system.

Good video as usual Derek. However, one point! The 70kw maximum for domestic engineers usually applies to an individual appliance, not the aggregated total for the number of appliances in the property, unless they are in the same room. For example 2 boilers linked together. The size of the gas installation is the governing factor.

Derek my boiler heats my hot water in a cylinder and heats my radiators is this a ‘system boiler’ ? What would be the most efficient flow temperature I should set the boiler at? as at the moment I’ve set it quite high and I do not get the ‘plume’ I see on other condensing boiler exhausts . Is this due to the return temperature being higher than the condensing temperature of 50 degrees C that I think you mentioned regards

Turned my water down to 45 degrees and also the preheat function is now off. I switched off my weather comp on my Worcester as the heating was on longer than necessary and using more gas. It’s a digital one so it comes from the local weather services via a Worcester server then the controls are updated. Maybe then I also had all radiators on maximum.

I hit the like button 983 times 👍

8litres a minute struck a chord! Flow rates in my area in the south east are generally poor. But when I cast my mind back to traditional tank fed hot and cold systems, over the years the skills of plumbers of old who understood the relationship with head of water and pipe sizing has diminished. Consequently end users have generally got used to lower flow rates, especially with the advent of ceramic discs and flexy connections. When consumers, especially any with cylinder storage systems, are made aware of the energy they use to heat water; in conjunction with the price of energy, I can see major lifestyle adjustments. Provisionally, my meagre research suggests a two person household consumes 2-7kw per day in gas to heat water (combi-storage). Given 6-8kw for heating your average home (given -1C ambient), the hot water side of the equation takes on takes on a whole new meaning. In summary to repeat what you've said, range rate your boiler, lower water temperature and with stored water also heat only immediately before use.

Very right Derek but again it is down to these paper and plastic gaa engineers that actually only know what they are fed to believe, or know the best priced boiler against the easiest to fit, if it works or not, to make as much money as they can. The ratio of temperature output to temperature return to them has nothing to do with it as it is not marked on the box. Throw a few thermostatic rad valves in just to complete the non-working condensing boiler circuit. Which as a role the circuit itself is bought as a pack, as in an 8 roomed house you need an 8 rad pack, to fit them where they fit, which has nothing at all to do with a condensing circuit and very few would have any knowledge about that or how to design one. That is for new builds as of course older existing systems were never designed for condensing boilers to work as they should. As you know it is more the ink is still wet on the Gas Safe plastic so whack them in boys as we will be on doctors money in a few weeks.

How many kw is needed to heat 9liters a min by say 35c I personally have range rated my hot water to 15kw and have it set on 45 at moment and it runs good for now Very good video derek. I think consumers are switching on to having an efficient system now with the bills being so high

Hi. I'm not a professional, just a consumer. But unless I have missed something in this video, the larger boiler uses less gas, so surely it would cost me less to run. Is that correct?

Hi Derek, great educational video and certainly food for thought in these energy conscious times. So staying on that subject, you hinted on one interesting subject 'Range Rating' almost a black art subject. My question is this, concidering very new system boilers, what's the difference between 'range rating' and 'modulation' All I understand is RR involves changing fan speed, so can reducing a 30 Kw system boiler to 28 or 26 Kw at the same output temperature realy reduce energy consumption and if so how. Maybe there is a very clear explaination on line that you could link me to. Kind regards Dave Porter

Derek a great set of videos , however i have range rated my Worcester Bosch Greenstar boiler down to 8.2kw , reduced my ch temp to 62 , the return temp sits at 54. this is the first time the boiler has actually been condensing however a fault code EF 349 The boiler’s operation is at a minimum burner load has shown up , is this something to worry about ?

I’m hoping to keep my combi condensing longer this year by having a very reduced CH flow temperature so my return temp should be much lower.

Good video, explained in laymans terms. Its a shame that it has taken the energy crisis for everyone to talk about modulation, condensing and range rating.😉 I have a Vaillant 837 which was bought for the 15ltr flow rate, as I have 2 en suites. It was installed in 2009 and has been running at max heating of 29KW! There was no talk of range rating it and weather compensation etc. I've worked the heat loss out on the back of a fag packet to about 11KW, So have now range rated it to the min of 12KW. It will interesting how it performs this winter. Back to the Video, I'm not a gas fitter, but even though the higher rate boiler you were testing didn't seem to be able to keep to the hot water temps you in putted! It used less gas, so would be cheaper to run.? I think this needs to be looked into to further👍

Quick question for everyone. My rads are cold at the bottom (2 year old system so not sludge). I run the system at 50 degrees for the reasons derek says in this vid. Is that the reason for rads being cold at the bottom?

Surely you can adjust the tap flow using the service valve.Most plumbing has them these days.

Top tip, if you have a cold-fill washing machine and a combi. Fill a watering-can with hot from the tap, then pour that into the machine via the detergent drawer when it's filling.

4 Bed Semi with Navien 37kw 500NCB combi boiler fitted, max hot water flow rate is 15 LPM, Hot water temp set at 45 degrees, 2 minutes hot water with digital thermometer 46 degrees, 1.7801 kwh used in 2 minutes

Why don't al boilers have the ability to drop the kw output . Most of the time the boiler is cycling .

Hi Derek, Why would you use a heat only boiler instead of a system boiler? If you have a solid fuel stove/range and the water from this open vented side of the system shouldn't pass through the heat exchanger of a gas boiler wouldn't a system boiler with an additional heat exchanger installed always be the better option over a heat only boiler when you can't fully avail of the open vented system already in place. If the water from the gas boiler and the solid fuel stove are allowed to mix then I can see the benefit of the heat only boiler. Is this correct as I have been told? Thank you for your time 👍🏼

I just had fitted a 32kW Ideal Vogue combi. The water flow from my tap dictated the boiler size so the boiler is over sized for my 12 radiators even allowing for modulation and the lower output for heating. If the heating is run at a lower temperature is that doing the same as range rating as my boiler can’t be range rated?

Viessmann boilers can be range rated down to less than 3kW. Intergas come close too

Not really revelant to my system boiler installed last ear. 30Kw. I had a conventional 80,000BTU floor mounted CF. The installer said we take about a third so = 30KW. Well l it has cut gas consumption b a massive amount but kept the house warm. So happy. Just had it serviced t £90. The old one hardly needed looking at so there is a new cost.

3 years ago I had a boiler failure so needed a replacement next day. Went for BOX but had no time to do a survey of house and radiators. They provided greenstar 30i with Google next. I found out later that nest is not compatible with bosh Worcester controls so only does on/off. Most of house had been plumbed with 8mm micro bore but I replaced downstairs with 15mm and installed smaller but double, finned radiators. Much better heating than 3xs longer one but then realised boiler set to 80deg. Tried 50 Deg but not heating rooms to 20. From tomorrow I'll do a full survey. Thinking talking to Bosch about modulating controlls. If not scrap it and go for heat only and elec instantaneous heaters on the 2 sinks. 2.5 kw instead of 26 kw from gas boiler plus time and heat wasted until water runs hot. Comments please?

👍👍👍👍👍

Hard to believe that 80% of UK houses have combi boilers. Are 80% of UK houses really sub 2 bed, 1 bathroom. I have a heat only system and the biggest problem is the radiators just aren't big enough to lose enough heat so they get very hot but the house can be cold and the boiler constantly cycles.

Stupid question how to restrict my water down to 9 litres per minute plz.

Isn't there a problem with low temperature hor water. I was under the impression that hot water for taos etc should be at a minimum of 50 c to kill virus and bacteria throwing !

🤘😎🤘🇬🇧

Very knowledgable, but I still don't know how to add the mystery device to my combi boiler.

I personally dont see a need for hot water storage in modern homes. when most of the time we use very little hot water. Hot water on demand that a combi gives i think is more cost effective. For example My gas bill in summer my daily standing charges were more then the gas i used. before i had a combi it was much much more, having to wait an hour to heat a tank up, just to fill a sink up isnt good enough for a modern home.

If combi boiler does or can heat hot water and heating at the same time? Is it cheaper to take bath/shower at the same time when combi boiler is on?

At the end should be accept not except

I find a 26kw combi the perfect size

My vissanman 100w can modulate down to 8%.

Save yourself alot of money and find a Viessmann installer to fit a Viessmann 200-W. No other boiler is as efficient with such a low modulation ratio!

Perhaps the Government should insist upon water companies providing warmer water in the mains! This would create far less need for heating in the home, and have an immediate impact upon the emissions. This could be achieved in many ways like covered reservoirs - high installation cost but long term advantages! Maybe installing water mains at below 2.5m would take advantage of the geo- thermal ground temperature of 52 degrees(?) Warmer water into the home would be to the long term good of the planet- or would it? Loved the videos and applied simplified checks that anyone can do! Thank you! I am moving house soon and need a total review o the systems in the new house, which is beyond my comprehension! The General public are unaware of anything like this tutorial, and are at the mercy of the installers recommendation! I have never had any explanation of the pros and cons of the various boilers, or suggested settings described! I recently had a complete new Combi Central heating system, with new convection radiators, and have not yet even set the programmer! I just turn it on as needed! Ariston One boiler, 6 rads, and a lot of mess! Total charge £9,000 ! Seems a lot of money given the advice in your tutorial! Having completed the new installation we then found our dream home elsewhere, and now need to look into the whole system for the Bungalow!

Who cares if it struggled to modulate if its using (16.27 14.65) / 16.27 = 10% LESS gas?

What a waste of time.