If the Nest doesn't have a common wire connection it will power steal from the other connections, but only when it's not running. So on a really cold night its internal battery can deplete and then it shuts down. After a few hours the internal battery recharges and then it starts working again. I'm a Nest certified pro. I've installed thousands of them. 90% of service calls are related to the C wire not being connected.

Ted, I had the same problem in my house with a way oversized unit that would hit high limit. Trane XV90 to be exact. They changed out the burner orfiaces to a small size which helped some, lowered the gas pressure, increased the fan speed.... finally they soldered the orifaces shut and drilled them to a small size and it stopped hitting high limit. Ran close to it, but, didnt trip it out anymore. We also went to a less restrictive filter. It ran for years, but in the end, ended up cracking the heat exchanger after 19 years..... guess i cant complain on that one.

I'm in Michigan and had a 2 stage furnace 125K/ 84K BTU, 1985 vintage. Since I had upgraded the windows and added insulation, I found that the 125K was oversized. I permanently hardwired the thermostat to the 84K setting and never had any problem with ignition and always had nice blue flames. Even on the coldest day in winter, the furnace was adequate to meet the task. More recently, I had Carrier 2 stage furnaces (2000 vintage) and the control board managed which stage was in use. It could also be wired so a 2 stage thermostat would determine which stage to use based on whatever logic existed in the thermostat. I don't know anything about those Nest t'stats, but maybe they're 2 stage capable. I know this video is old, so you probably solved the problem long ago. I like your videos and your calm, no nonsense approach to problem solving.

I am not in the business. I like watching your problem solving and the way you talk yourself through each of the scenarios. Great logic ( at least to me) is used.

Hi Ted, I wanted to add my thoughts about Total Static Pressure Test that may be of use to you and your readers. With the test, the probes are positioned in the recommended places on the equipment as indicated and a measurement is taken. So, if high, you might look for restrictions closed baffles, dirty filters, undersized ducts, etc.... One thing to remember along with the usual suspects is don't forget restrictions in the return portion of the systems when doing total pressure. Inadequate return flow between rooms can affect it. I open all doors in the home to take my first measurement , and then take a second with all doors closed to see the change. There could be significant static pressure in the room its self. You could check using the manometer as well. If you are on the edge adding an additional return to a room may keep you in the limit.

Anti DIY, I had a similar situation once and had more time to find a solution. I used the manometer to check static pressure on the supply and return ducts/plenium. I found the return side fine (.23 wc) but supply side high (.75 wc). Customer didn't not want to spend money for me to install more supply ducts or redo ducts at the time, but agreed that she would have me install whole new system in the summer It was easier for me to install a bypass 6" duct between supply and return duct with a manual damper in the middle. I was able to decrease supply side and increase return air, which was not ideal but stopped the high limit from going off.

Another great video Ted. In most furnaces you can see the speed taps on the diagram sticker inside one of the furnace doors. I ran into this issue once on an oversized Trane XB90 furnace and I did exactly what you did here in this video. But I also made a small opening on the supply duct right above the furnace to heat the furnace room in the basement. Customer called me back a year after for furnace cleaning and said everything was good after I made the change. ( upflow furnace; no flex ducting)

Ted needs a service man for his van, "tire pressure monitor", "change engine oil soon". His van has 235,432 miles already...

up next, the husband is turning it off at night to keep the wife from chewing up all the gas and cooking him out LOL

I would have just taken the easy route and blamed it on the Nest thermostat. 😂

If you're supply was 130 mixing at the register it was probably 135 at the takeoff. Return temp was perty high too I think in about of the manuals it tells you not to run a higher return temp then 80. Most furnaces i see are anywhere from 25 at the lowest and 80 at the highest which is way high in my opinion on the temp rise. I think 40-45 is good most the time, leaves room for a dirty filter or shut registers. Only think you really can do is derate gas, increase Airflow at blower tap,check shut registers or add ductwork if issue persists. Ultimately go in with smaller furnace as last resort. Nice video

12” only handles 500 cfm 10” 300. Bumping up blower speed may help high limit but it also may over amp the blower motor if the return is also undersized. Why do some people think you can only draw return from one side of the furnace?? I often used the back or the opposite side to draw RA along with the main. That’s one of the best looking attic installs I’ve seen on your videos. I would make it mandatory for your installers to do a start up before they leave the job!!! I never left a job with/out a start up unless it was new con with no power Never never a change out !!!

Hi Ted: I had a similar issue with a furnace and had to add a return duct and to get more air flow. Also turned down gas valve but furnace did not light well after that, so had to increase a little to get a good light without a bang. Also filter size was small and recommended to increase the size in the return and use a low flow air (cheap) for better flow. Thanks for fixing that hard to fix problem.

Been watching alot of your videos lately before subscribing and can't believe the number of shoddy installs in your area

I would recommend : 1. Static presure test than compare to the blower chart . Check pressure between the coil also 2. duct calculation to see if you can move 1170 cfm with current ductwork . ( that's what's needed for 90k) Just going of the experience to me its undersized - I usually run 2x14" returns on 75k furnace-3 ton set up 3. Add 4" filter( get rid of 1") 4. Maybe even increase motor speed to high if needed , ( rheem has tap that you can share same speed cool/ heat) not sure about carrier Hope this helps!

Nice job Ted, I always look forward to your videos.

This is a good tip for remembering fan speed: black is high, its the coldest color if you think about it. Blue would be med high because it would be the next coolest color, followed by yellow being med low, the color is getting warmer with red being low speed. The lower your fan speed the higher your temp rise. So low speed would have the highest temp rise. Make sense? Purple is usually med on 5 speed motors.

For me its weird to see an upflow in an attic, I'm from Illinois where alot of houses have basements. I've dealt with horizontals only in attics here. Mostly air-handlers too. Crawlspace installs are BS also.

Hi there HVAC guy. Good job of one handed repair and diagnostics!

experience is the best tool,just watching u work tell,s me u got lot,s of it!!!

A big problem in that house is as the furnace is running the return air is sucking in a lot of the heat from the registers. Your return error was 82 degrees and I'm sure it would go higher as the furnace runs longer. Because you have ceiling Supply and returns one way I've been able to get around that is going to the supply grills bending the veins downward. Make the Heat come down as much as possible. And if you're by Windows you can make it come straight down. That's one of the problems at that place you're sucking in heat from the supplies heat stratification is happening. Furnaces are not designed to run with 80 + degree return air temperature. You'll trip a limit every time

Every time I hear that phone ring I think about $$$$$$. 🤣😂 That's MONEY calling you!!!

Check static pressure, Return, supply and drop across coil. Remove high limit and put inspection camera up into coil to see if it’s dirty. Check all supply registers to make sure they are open, adjust if needed. Open all bedroom doors, if there are no returns in the bedrooms they will over pressurize and choke off the supply air.

You may have to remove the first orifice and cap it and run only 3 tubes instead of 4... And recalibrate to get the proper heat rise temp. Heat rise should be taken at the furnace suppy and return. TSTAT may make temp before High limit at 160 degrees trips.. What you did may work depending on run time...

20 seconds in and see it doesn't have enough return !

Nice video. I would have done exactly what you did but left customer with option of a dump zone or replace furnace. You have to have more airflow for 90 btus. Thanks for sharing

Another good one from Mr. CooK!

Great video, thanks for all the detailed explanation too.

Furnace Skematic usually shows fan speed on icp but that works 2. Looks way short on return. Carrier has 90k btu 3ton furnaces. That's prob a 4 ton drive. Need to check the drive if 3 or 4 ton. Supply is 3 1/2 ton so seems fine 2 me.

with icp furnaces previous they had smart valve pilot in middle which seemed much safer to plug one of the outside orfices still static pressure could be high with blower tonnage it was much easier in old days to make something work than now now with everyone knowing more than the one that was called nice presentation

Nice clean and logical approach and comments!

You are a professional thank you for your videos

To anyone that watches Mr cook videos your watching a true old school pro that cares about his family people I think there people he loves and cares about I know you say what there clients no your wrong he loves what he does gods work going we get to witness when people really care for each other I think it's really not about money it's what God sees in use love you Mr Cook

blower speeds and full wiring diagrams are usually available on the furnace doors.

I've used Klein probes. Nice and robust. The ones I've had were previous versions that didn't have the magnet. Now that I've seen this new version I may get one because that was my only gripe.

I seemed to find The 1” pleated filters always have a restriction,, plus flex duct move a bit less air as metal , so we always ran the next size up on flex , okla.state Lic.# xxxx

Thx. Something to watch instead of tv. I suppose raising fan speed will shorten the run cycle unfortunately.

Hi Ted. Thanks for all you do. Love your work! Learn a lot from you. Just a suggestion, but, my thoughts are to run a total static pressure test when changing fan speed along with gas pressure that you did. Also temp rise...you also confirmed restricted airflow. Curious, did you check filter in the home? I'm pretty sure you did, but just didn't mention it on video. Thanks Ted!

Those white rodger valves come set high like that from the factory on Carrier products. The installers did not even check the gas pressure and left.

I know that this is how it is done all over the United States (you don't have to tell me that) but having ceiling returns and ceiling supplies only works efficiently for "cooling" where you are taking the hottest air in the room back to the air handler to have the heat removed. Having high wall/ceiling returns for heat simply takes out the nice warm air and leaves the cold air in the room. It is a little more complicated than that. For my own personal use I use a high-low wall return set up that is dampered so that it can be changed with the seasons. Makes a world of difference.

I'm thinking that eliminating one of those jet burners would be helpful in this situation and capping off the Spud for that unit. But that's an idea to try. I would likely do a center jet burner if it didn't rely on the wings to ignite the next one, so, your probably going to do the end. Would also turn the pressure back up to 3.5.

Couple things I have done with this type of problem is 1st I have removed one of the orfice and put in a plug and relocated the flame sensor, 2nd I have removed some of the vents say a 6” and made them 8” to get rid of more air 3rd would be to add more vents to different parts of the house or garage

i would just plug the last burner away from the flame sensor,that will decrease the temperature rise and it's safe to do it

As another put it. It's all in the engineering. Thought I was watching myself work, only I'm not as good looking as you. What I do is tell the customer he the unit is oversized, and re-engineering the ducts are required. This includes possible return additions, larger ducts, replacement of all stamped registers. In addition to what you did, add drops, and dump into coldest room or unused room if possible. Get the external static down, kill the high fire if possible. It can be done, but I don't re-engineer the units themselves, as far as jets go for legal reasons, only on cars. Others may be more daring then a old timer like me. I have pulled a duct off a plenum to get them by until a reduct could be done. Temp rise was still high after what you did. One old timer to another.

Great video Ted.

I like that case for your manometer has everything in it nice

I have ran into same problems before. Customer says well we planned on adding on to house but never did at least they were honest. I never go below 3.1- 3.0 high fire. Speaking of high fire you pulled that monometer hose off gas valve I was tensed up untill you put cap back on lol think you did that on purpose. Great video I would add to do quick CFM check on all supply vents before you leave especially since they had manuel dampers. Also while you have that fancy monometer check duct static pressure see if you have any insulation gremlins on your coil. Thanks for videos we appreciate you :)

After all that, my next operation, and I have done this when I had no choice is to block the orifice on the last burner, the one with the flame sensor, disabling it, then moving the sensor over one burner. As long as there isn't a thermal limit in that exchanger tube, it won't hurt a thing. Then adjust gas psi if needed. I have gone as low as 3.2" or as the manufacture suggests. Of course the best thing to do is install the properly sized equipment.

Add 1 8" inch duct anywhere in the house that customer prefers and you'll be set👍

I'm wondering about the moisture/rain/condensation stains on the exhaust flue and below that on the manifold, which also looks to be getting onto the flame sense wire/part. I wonder if it's condensing on real cold nights and wetting the flame sensor/wire causing a lockout :)

To my knowledge yellow is a medium low speed where blue is a medium high speed. Low - red Medium low - yellow Medium high - blue High - black

Do a static pressure test to see where you are running also could do a combustion test when adjusting gas valve to make sure that your ppm is not above 100 there are combustionVariables for different types of gas units you can look on Testo or Bacharach website for that information

@22:52 You have LIDL grocery down there too now.... What do you think of it? Produce and bakery is mainly what I will go in there for.

I think it's really interesting how it heated from 71 to 80 degrees in 10 minutes with the vents being on the ceiling. Heat usually does better coming from the floor.

Maybe check the static pressure and see just how restricted it is ? Add some duct work and correctly solve the problem ? And why now is it shutting off on high limit ? Unless it’s been doing since installed ? I think more investigation needed to be done !

We just replaced a perfectly good Keeprite , trouble was previous company installed a 100 k 2 stage in a 1500 square foot side split . They only thing we could do was install the right size 60 k . In Canada we are not allowed to modify furnaces by plugging burners , nor would I. The only solution Ted is a new 60 2 stage

Downsize oriiface. Or block off burner but looked like you would have to relocate flame sense

I've often thought about shutting down one burner and dropping back the gas pressure. Not sure if it would work or not but it's a thought.

@22:17 😱: Two sets of solid double yellow lines that are two or more feet apart sometimes appear as a road marking. Such lines stand for a solid wall. Don't drive on or over these road markings. You may not make a left turn or U-turn across it.

Note fan speed on wiring diagram. Check static pressures. Compare to fan chart. Should be easy to find online being a 2016 model. Check temperature rise and gas pressure. Good chance that evaporator coil has gotten more restricted over time and is just now starting to impact the heat exchanger. Check the static pressure differential between the outlet of the furnace and the outlet of the evaporator if you get a “call back”. I agree it is too big but they may not pay you for a new furnace and just live with the problem but they may pay for a coil cleaning and a larger return duct or two. Give them both options. A band aid solution and a few permanent solutions. The customer has to own the decision.

Good job Ted.

Thank for the video. I had my furnace replaced 3 years ago and it was oversized. It countinued to over heat and shut off and turn back on right away. Ive had the technician out 7x now though out the install to try to fix. I was told by a different hvac tech that the has was tuned down to temporarily fix the over heating. Well now its in the negative cold snap here in Chicago and my heat cant keep up with the -10s and 20+degree windshield. Runs all night for few days stright sometimes dosent shut off. We went to bed and it was 74 degrees woke up and it was reading 68 degrees in the home. Had to buy a space heater to make it though last few days. Different techs who came out said the furnace installed was to large for my home. Also the return air duck was to small. They said the downstairs area could use a return because it dosen't have one. My question is, is this issue fixable and is the contract responsible for rectifying this problem with the correct size furnace. I have a warranty company that i use and they now said they aren't going to replace it, even though they admited to the contractor they used said the new units to big. My old furnace never had that problem before. Any recourse you can recommend be greatly appreciated.

I'd put a temperature controller like a Ranco sensing the discharge air temperature on one of the main branches set to cycle in series the white thermostat wire from the thermostat to the circuit board of the furnace to shut off the burners when the discharge air get too hot and under the high limit temperature limit. The the burners will short cycle on long runs but the furnace would operate as close to normal as possible and the home owners most likely would never know the difference.

Pretty sure if I seen that right the black fan speed wire should have been on the heat tap , where I work we never chang the heat tap , just change for the a/c size

Sensible load means nothing if you cannot move the right amount of air. Little more return and supply would be great. Does anybody ever do combustion analysis anymore? Most important test on a gas furnace. And it can give you signs of overheating problems.

It’s all in the duct work

I capped the last jet moved over the flam flame sensor everything was a okay give that a shot nice video thank you

50F temp rise sounds pretty decent unless it has a low range like 25 to 50 vs the normal 40 to 60 - or it would be if the return wasn't pulling in such warm air due to location. Why not put both heating and cooling on high? Just need a jumper wire and Y connection/splitter. No pro, but i've observed going up only one speed doesn't drop the rise very much on undersized ducts.

had the same issue in our home for 12 years. 80,000btu in a roughly 1,200sqt home. For the first few years the company could not figure it out, so they say, they were just trying to brush us aside. What helped which was not ideal, in the winter remove the air filter, open up a second return air and open up another exhaust. This helped but on really cold days it still tripped the high limit and we had no heat until we turned the furnace off and on. We finally replaced the furnace a few months ago and got a good HVAC company to come in and we currently have a 2 stage 40,000btu & so far for the past 4 months no issues. Makes a big difference when the company knows what the hell they are doing lol

Do you ever get your instruments calibrated? (gauges, manometer, IR thermometers, etc)

Your videos ted are 10/10. Not anything like that hack from New Bedford

I'm not big heat specialist so your videos are very educating for me. Thank you. I'm little bit crazy about duckt sizing. My solution here will be add extra return and extra supply register. At least 350 CFM . Will it help?

WOW great video, had the same problem and my guy did just that , lower gas pressure and fan speed medium high and problem were fixed, and yes my furnace was to big for the house

Curious if you use a flat rate system and if so which system? Thanks

Plus put a relay in there that makes the fan run on high in both heating and cooling

Nice job and video

Well you can always under fire it like you said. Never over fire. Is there no filter on the return?! Maybe the Acoil is filthy?

How did the customer react? Are they considering replacement?

Another great video! I also have an oversized furnace & inadequate ducting, but the tech actually set the fan to spin at the same speed throughout the cycle. It no longer hits that second stage where it spins faster. Is he wrong?

Nice video.

90K BTU, 17" Wide, 1400 CFM. Furnace being fed from the side with that small pipe (likely a pleated filter too). Yes the furnace is suffocating and the limit is tripping. Have seen it with other ICP brands as well. Likely a 70,000 would have been more appropriate. The 90s can be finicky with overheating.

Wire diagram is right on blower access panel or main panel. Carrier , bryant, payne all have wire schematics to motor wire tap. If you have an ANDROID phone there is a great app for almost ALL makes and models with all install manuals available called FURNACE CODES AND DIAGNOSTICS by Fire-n-ice on google play store. excellent tool to have as well as the carrier service tech app for all replacement components

Pull 1 orfice and install a blank, brings it down to a 70,000 BTU in the ballpark. Hack, yes, Works, yes

Nice job

A 12” return isn’t enough. Static pressure across the unit would have removed the guess work. Adding a 12” return and an 8” supply spill duct/register in a hallway would help immensely. Kicking up the blower speed could be objectionable noise and drafty

I went on a call a while back and they had a hundred thousand but furnace in it but the duct system was to small to move the heat quick enough and it tripped high limit every time so I capped two of the burners off moved the flame sensor it fixed the problem there again they sold the people more expensive furnace than they needed

What gets me is that he checked the gas pressure but never checked the static pressure. The supply ducting looks 'ok', but the return duct looks small, what size is it? Also, didn't he notice all the oil leaking from the blower motor for a 2016 model, defiantly says that the static pressure is way high and the motor is overworking trying to move air. May be a oversized furnace, but I suspect the return duct was too small.

Ted, could you have sealed one of the burners closed and only lit 3 instead of 4? I realize you don't want to rig it, but was wondering if that would effectively make it a 3 ton. Not a HVAC guy but am learning

Check the CFM chart for Med High and see if that will work for 3.5 ton. If it does, put the heat in High set cooling to med high.

Could or can you block out a burner from 4 to 3?

Looks like you should check your motor in your truck also!

Does installing a 2-stage furnace pretty much make the problem go away, other than having over payed for a too big furnace and not making use of the high-stage?

On a Standard Stactic Pressure at 3.5 they have 1400 in Duct which is what a 3.5 calls for js

what happens if the existing gas orifices in the manifold were changed out and lowered to your desired 60,00 BTU sizing?

I’ve never seen a regulator needed on internal distribution lines, only at the meter or in certain appliances. Does SC not put regulators on the meter outside the house?

whats the delta T across the heat exchanger? Is the gas valve a 2 stage valve?

No heats are my favorite calls to do

Could you not take out one of the burners in the heat exchanger and just run 3 not 4 and take 25% off of the btu? I’m not a hvac guy just a thought.

Before saying that the duct work is inadequate, you should check static pressure on duct system and unit and then make that assumption. 2-10's and a 12 is fine for 3.5 ton unit. That's 1800 cfm for a 1400 cfm unit. Only if the return was less than a 18"would I say inadequate. Also before doing your gas pressure test you need to have a thermometer on the supply and return to check your temp rise and to make sure your in range. If you drop that gas pressure and your delta t drops Below recommendations, than you"ll be back to turn the gas back up. You residential guys are lazy or dumb. You guys should always look to make a call fast thinking you guys know a lot. I suggest you get the field peice probes that connect to phone or tablet via bluetooth to get all that info while you change your gas pressure test. Always work to sell a unit and not the problem. Not a hood mechanic in my book

What will a to big furnace do?