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Author Topic: My furnace keeps burning out thermocouples...  (Read 12415 times)

Offline Adam B.

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My furnace keeps burning out thermocouples...
« on: November 18, 2011, 07:48:31 PM »
Hey guys...

I thought this seemed like the best area to put this question on the boards.

Has anyone ever had trouble with a furnace that keeps burning out thermocouples — at the rate of one every 2 weeks (or less)?

We moved into this house last December and I have replaced the thermocouple on our furnace FOUR TIMES now (over the last 2 months).

We had a good HVAC guy (independent so he wasn't very expensive) come replace them on our water heater and furnace (we were having other issues) and he used a better thermocouple on our furnace than the ones you can get at Lowes — however while it lasted for the remainder of last winter — less than 2 weeks after I fired up our furnace this cold season it burned out.

I have since bought 5 more from Lowes — the only place I know to go in a pinch to get them — and maybe they are just garbage...

However I have NEVER had to replace thermocouples like this on any other furnace I've ever had. The ones I have bought from Lowe's seem to last about one to three weeks and then they die.

I have been buying them two at a time in case they burn out when it is cold I can swap them quickly — but no matter how careful I am to have them only slightly touching the flame etc — after 2 weeks the furnace is DONE.

IT always seems to happen when the temperature outside dips below the freezing mark (below 30) — it almost instantly burns them out — but when it is warmer out — say 40 - 50 they don't seem to burn out at all.

I cannot fathom why that would have any effect since the pilot light is constantly running.

However, I am going to start shelling out more in thermocouples than natural GAS LMFAO...

I'm JACKED — no pun intended lol — but we are at least prepared with several electric heaters and kerosene so this is not ever going to be a survival situation where we are freezing to death!

It is just much easier to turn the dial on our thermostat than to run around the house turning electric space heaters on and off all the time!

I'd appreciate it if there's anyone out there who has experienced this before and knows what to do!

PEACE
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Offline endurance

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Re: My furnace keeps burning out thermocouples...
« Reply #1 on: November 18, 2011, 10:26:58 PM »
PM mxitman, he's an HVAC guy and he's been very helpful with me and some of my issues.
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Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #2 on: November 18, 2011, 11:13:15 PM »
Thanks man. I actually forgot I had a spare complete burner assembly for my water heater so I pulled the thermocouple from it and got the furnace fired up in a couple minutes. It is only a matter of time before it burns out though. From what I've read I could need a new valve but the hvac guy I had look at it last winter said it was fine and he tested everything.

I'm gonna run out to find a better quality thermocouple in the meantime to have when this one dies until I can figure out why they keep going bad.
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Offline JerseyVince

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Re: My furnace keeps burning out thermocouples...
« Reply #3 on: November 19, 2011, 09:58:35 AM »
Maybe the pilot is adjusted too high? or you're having the flame back up due to dirty/blocked orifices or poor venting thats burning the thermocouple up. even crappy thermocouples should last a season

Offline mxitman

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Re: My furnace keeps burning out thermocouples...
« Reply #4 on: November 20, 2011, 12:00:49 AM »
A couple of issues I see;

1) if I replace a thermocouple and then have to do it again in 2 years or less then I also replace the gas valve and/or assembly. Could be an issue with the gas valve, kind of strange it's doing both on the water heater and furnace...

2) most thermocouple are universal but Carrier/Bryant and a few others units sometimes use proprietary parts and may give off diff readings than standard universal types.

I recommend to upgrade your standing pilot to a hot surface ignition using a nitride igniter on your furnace...they last forever. Might cost a few $$ but if your not in absolute need of it, and just tell your independent HVAC guy whenever works for him...should be less than $300... some can be done pretty cheaply just depends on what kits fits your furnace.

Other than that...clean up the thermocouple threads really good, make sure everything is fully seated and tight...
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I'd rather have it and not need it, than not have it when I do need it.

Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #5 on: November 21, 2011, 07:02:14 AM »
No it is just the furnace. I replaced the water heater thermocouple and its been fine since. The only reason we called an HVAC guy to do it in the first place was our water heater went out and THEN we found out it is some crummy Lowe's job that takes a special reverse threaded thermocouple that they don't even SELL anymore ANYWHERE. I ended up finding out via the internet by someone ELSE who went through the same thing that the water heater company makes a new burner assembly and they will send it to you free of charge — and it comes with adapters and everything to accept a standard thermocouple...

Well — at the same time we were waiting for the burner assembly — the furnace went out in the middle of the night — so after 4 days without showers sitting in a house when it was -10 outside (coldest week of last winter) with NO heat of ANY KIND we flipped out and called the HVAC guy.

He showed up and spliced a new thermocouple to the old one by cutting the copper, pulling out the wires and soldiering the new thermocouple's wires with the old one's reverse-threaded end piece — something I had not even thought of myself! It has held tight and works fine to this day almost a year later — and I have a new burner assembly (sans thermocouple lol) sitting in waiting for whenever it does go out.

He checked over everything on the furnace and it is fairly old but he said it was fine and a new thermocouple should be all we need. The one he put on is fairly robust compared to the ones at Lowe's I've been picking up. It lasted all year. I never turned off the pilot light all summer either and it worked fine until the cold weather came along and snuffed it out.

Now I am replacing them every 2 weeks since. I use a mirror and make sure only the tip is licking the flame etc. I even watch as the furnace fires up to make sure extra flames are not brushing on it and they are not. There is just no reason other than what I have read that the magnet inside of the gas valve assembly could be wearing out and whenever a thermocouple's voltage drops slightly after a few weeks of use then it no longer has the strength to pull the magnet open anymore…

That is the only thing I can think of right now. I don't think I can replace a gas valve myself but I can see how it would be done I think. I probably know someone who can or I cannot imagine it would be more than $300 for the HVAC guy we know to do it. We are just broke as all hell right now and may end up being homeless by Christmas as is.

I am probably losing my job this week and we are basically getting ready to live out of our truck so I don't want to sink any money into a place we won't be living in anymore unless I can do it cheap :-)
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Offline Perfesser

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Re: My furnace keeps burning out thermocouples...
« Reply #6 on: November 21, 2011, 10:28:22 AM »
Found an interesting post on thermocouples here:
http://www.wardburner.com/thermocouples.html
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Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #7 on: November 21, 2011, 03:59:16 PM »
My girlfriend just called me to say the one I just put in on SATURDAY already burned out and our furnace is off again.

One of the other ones I installed lasted 3 days too.

I cannot even fathom what this is going to cost us. Unfortunately we got sucked into a "rent to own" deal on our house and we are required to fix anything when it breaks but we will actually never own this house (we ended up with a deal that still saves us a ton of money over what we paid for the last place I lived in rent — but we never had to FIX expensive problems at our old house).

I highly doubt we need a new furnace but I can't be replacing 3 or 4 thermocouples per week either.
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Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #8 on: November 21, 2011, 04:04:25 PM »
I think a new filter might be in order after reading that article. I meant to try that but didn't have any extras laying around. The problem is that I have to take apart the duct where it enters the furnace most likely because my son shoved a bunch of plastic balls down the cold air return (does not block flow but I have a feeling some are up against the filter screen and will enter the furnace if I remove the filter).

LMFAO — the joy of 2 year olds!
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Offline JerseyVince

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Re: My furnace keeps burning out thermocouples...
« Reply #9 on: November 21, 2011, 05:37:15 PM »
when you say burned out, do you try to relight the pilot? how do you know the thermo is bad, do you check it with a DMM (OHM meter)? I had a similar problem that was traced back to a partially blocked gas line in the street after i replaced two gas valves thinking they were bad, i had good pressure 7psi but low flow, the boiler would starve for gas as it ran longer and would shut the valve because of low pressure

Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #10 on: November 21, 2011, 09:27:56 PM »
Yeah I would try and re-light the pilot and it would just cut right out as soon as I let up on the button. Putting on a new thermocouple and it stays lit the first time every time.

Tonight I replaced the air filter and put a new couple on it, making VERY sure that only the tip is sitting in the pilot light flame. It started right up (have that process down to about 1.4 minutes LMFAO).

I have a pile of "burned out thermocouples" and I do not know where my multimeter is if I even have one anymore. We moved last winter and life has been such chaos my basement is still a bunch of random piles of crap. I have taken the time to neatly stack them and keep my camping / go bags / etc like that all tidy but then I go on a wicked camping trip and when I come back all exhausted it gets tossed into a random pile and takes several weeks to get sorted again even though I am pretty particular about cleaning everything before I leave camp — so it is not usually nasty.

I barely get an hour to myself every few days anymore with the kids etc.

I just kept all the thermocouples in a box so when I get a multimeter or find the one I know I had before we moved then I can at least test them. But, I assume they are messed up since throwing a new one on fixes the problem every time (until it goes dead again).

I bought a new one tonight and a spare in case it goes dead in the middle of the night — but if it goes down again I am calling the HVAC guy to come check it out.

I have no idea when the air filter was last changed since I've been here — which makes it a year at least LOL — but even though it had a lot of dust on it, it was this green meshy type (looked like a big scrubber you would get for the sink) and it didn't look like airflow would be impeded like the fine white cloth material ones you can get that filter a much finer particulate.

The one that was in it looks like you can take it outside, beat it, and put it back in (it is very heavy duty), but I figured to just get some new ones and see what happens.

We have lots of backup heat options but it just irks me when something like this goes down — but it is also a good lesson in being prepared for ANYTHING too.
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Offline mxitman

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Re: My furnace keeps burning out thermocouples...
« Reply #11 on: November 22, 2011, 01:54:57 PM »
good luck testing out your thermocouples..they produce such a small amount of voltage most meters can't read them. I have some high end meters...fluke etc $1K+ that I have to use to read them. Too bad were not close, gas furnaces are cheap. I only charge 800-1500 for a new ones..but in reality some furnaces only cost me 3-400 depending on size etc. Of course there are some that cost allot more, but no need to these days. If someone has a bad control board or fan motor...sometimes it's just better to replace the whole unit...

Sucks your in such a tight jam, maybe ask your HVAC guy if he has any newer used furnaces he could swap out for the cheap. I have people all the time wanting the High Efficiency models and they pay me $2500 to put them in and I get to keep their 2-3 year old furnace which I turn and sell on Craigslist or install for people like yourself....can do those for $250-500... easy money and everyone wins.

I personally would stay away from the HE models...lots of problems with them still, your better off with a 80-85% furnace with 3 speed fan and HSI (Hot Surface Ignition)...will last 20+ years if you change your filter ;)
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Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #12 on: November 24, 2011, 01:34:59 PM »
So far we've been good for the last 3 days since i swapped the filter and thermocouple.

We know we arent buying the house now because it is too small since i got full custody of my daughter. We did not want to do a rent to own at all because of crap like this -- having to fix everythig as if we own it but not owning it.

But because of the housing market right now it is much much harder to find a house to rent than it used to be. We did not pay any more than we would have for a straight up lease so we did it. Basically we don't want to spend money on a house we will never buy but we are stuck until the end of 2012 because of the lease.

The HVAC guy who fixed it last time said the furnace is fine so if we must fix it we just need it to last a few more months. We also have electric and kerosene backup and... Redundancy turns a major problem into a nuisance.
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Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #13 on: November 26, 2011, 03:00:45 PM »
Yup... Gotta call someone. Latest thermocoupke died in 4 days today. I have one spare but I'm so fed up with replacing them I'm not going to anymore.

If we are stuck replacing this furnace we are just going to go without it this winter even though it is against our lease. We are praying to god the roof does not collapse before we move because this awful rent to own contract requires us to fix everything.

I was totally against this kind of lease but we were almost left with no choice since this is how they are all doing It now and now we are getting hit hard. My credit is pretty much destroyed beyond repair for the rest of my life so I just try to live each day at a time.

It's impossible to get on your feet when half of your money vanishes because you havw bs credit and everything costs you 2x more or you need to accept horrible deals for the essentials. Even though we actuallysave a lot of money in this place vs our old place this kind of stuff is going to destroy us.
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Offline JerseyVince

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Re: My furnace keeps burning out thermocouples...
« Reply #14 on: November 26, 2011, 03:55:56 PM »
I asked my Uncle who is a retired Carrier HVAC Tech what he thinks and he said probably the previous repair someone moved the pilot burner or thermocouple too close to the main burner and its being overheated by the main burner. it agrees with your observation that the Thermocouples burn up faster the colder it gets as the furnace runs longer as its get colder Depending on your model there may be a little flame hood that can be adjusted to keep the heat off the Thermo when the main burner lights

When heated by the pilot the Thermo should put out about 30mv (milivolts)

Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #15 on: November 26, 2011, 05:13:03 PM »
The thermocouple does seem too close to the burner but the flames are not touching it. However the burner itself certainly gets hot and could be a culprit.

I talked to our hvac guy who said to run it full blast then turn it off after awhile and immediately blow out the pilot. The magnet in the valve should take 30-60 seconds to kick off and mine kicked off 5 seconds after blowing out the pilot.

He said if the control valve is bad then it will kick off very quickly like it did.

But he said that he has some old ones like mine in his spare parts and would only charge us the labor to swap it if thats what it ends up being. So looks like we can get it fixed good enough to limp through the time we need it for without a ton of money which is cool.

We were planning on trying to buy this house until I got full custody of my daughter and now the place is too small for us and we don't want to do any more improvements over what we have done already.
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Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #16 on: November 27, 2011, 09:40:45 AM »
Now the furnace went dead in less than 24hrs of replacing the thermocouple. Thankfully it is not sub zero temps right now but it seems like if our hvac guy determines we need a new furnace we won't be able to afford to replace it and when our pipes freeze we will get sued because we are required to did everything.

Based on an insurmountable debt we already have looks like bankruptcy in our future lol. I just give up. We are never going to get back on our feet after I was fired from a job because i went to the hospal for the birth of my son we haven't been able to get on our feet whatsoever. Just one "cf" after another every single day.
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Offline JerseyVince

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Re: My furnace keeps burning out thermocouples...
« Reply #17 on: November 27, 2011, 11:01:47 PM »
lets hope its only a bad gas valve and a few adjustments get you back on track. I hope things settle down for you and get a little easier this time of year is a big stress for everyone

Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #18 on: November 28, 2011, 08:07:22 AM »
Thanks.

I usually have a harder time once the time of year hits where I never see the sunshine. It is officially after sunset now when I leave work and Pittsburgh is cloudy all year to begin with (read a report once that we have an average of 53 days of clear skies — don't know how true that is, but those days are all in the summer anyway).

We can't even afford to get someone to come fix it until I get paid in 2 weeks since my paycheck I got on Friday is already gone down the bill payment toilet. I usually end up juggling $30 - $50 for 2 weeks the day after payday hits and I shell out everything we have in bills. We did succumb to the Black Friday BS since my daughter had a bunch of money from her birthday she wanted to spend and we ended up buying a new TV only because well — I have a craigslist notifier app that lets me know when deals show up and this TV was much cheaper than any used one that has popped up in over a year that we have been keeping an eye out.

But as usual, the SECOND my girlfriend and I spend any money on ourselves on fun or trying to find a way to relax — something happens the very next day and we end up screwed regardless. Oh well, we can watch a big TV while we freeze to death this winter LOL.

Once you get to the point you have completely given up all hope you tend to just live life each day and don't really care about tomorrow anymore. The fact we keep seeing the same TV for sale on craigslist for 2X what everyone paid for them on Black Friday makes me laugh and at least when we get evicted or whatever happens next we can get our money back without going to the store LOL.

I am just in a really bad mood right now. Every time we see a light at the end of the tunnel it ends up being a freight train about to hit me head-on.
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Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #19 on: December 09, 2011, 04:00:09 PM »
Our HVAC guy came over today and replaced the control valve with a spare from his spare parts collection that he pulled off of an older furnace. He has a bunch of them and was able to bring the correct one since I read the part numbers and info from the existing one.

He only charged us $80 for a service call and was finished in less than an hour.

If you have an older furnace under the same situation, the way you can diagnose if it is the valve or not is to blow out the pilot light after awhile of it being lit and running. Listen for the amount of time it takes for the valve to "click" off — which is easily audible. It should take close to a minute or so for it to shut off, and if it clicks off rapidly (in our case it was clicking off in less than 5 seconds after blowing out the pilot) then it is an indication that the valve is starting to fail.

If that doesn't fix the issue I'll post when / if we find another reason.
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Offline mxitman

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Re: My furnace keeps burning out thermocouples...
« Reply #20 on: December 10, 2011, 09:54:12 PM »
Ya Adam, I thought I had mentioned that but I must have forgotten to...Anything less than 30 secs I just replace the valve...hope that takes care of it...good deal on the swap out...
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Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #21 on: December 13, 2011, 03:27:42 PM »
Yes very much so. I was expecting it to be $150 at the very least to get this fixed.

Now, after he left — when it is cold outside it seems like my furnace is rapid cycling, but it does not seem to be due to a problem in the furnace itself since it only does it once the thermostat has reached its proper temperature.

My girlfriend said he made some adjustments to the thermostat — and before he came it was cycling to the point where the living room would get very hot before the thermostat (in another room) would kick the furnace offline.

Now however, once the thermostat is up to temperature — it seems to go about 5 - 10 minutes off, then the furnace kicks on and the blower doesn't even blow for more than 3-5 minutes max before it kicks right off. Before the thermostat would let the temp drop a little more before kicking it back online and running the furnace longer.

Will this shorter cycling wear out the furnace? Should I adjust this to have a little bigger delay between heating cycles?

It is a standard round honeywell thermostat. Upon popping off the cover the only adjustment that sticks out to me is the amperage adjustment (or whatever that is) and I read not to mess with it. Is there another adjustment I should look for on this thing?

It seems like the furnace should be on for more than 2-3 minutes between heating cycles even though I have been watching and the temperature always keeps up with the setting within a degree, and the furnace fires and stops heating properly.

If I let the temperature drop by lowering the setting on the thermostat, and then crank it back up, the furnace runs continuously until it reaches the proper room temperature.

Like I said, I think the HVAC guy adjusted the sensativity of the thermostat and it is causing the cycles to be very fast vs a longer delay and drop in temperature before it kicks back on.
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Offline JerseyVince

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Re: My furnace keeps burning out thermocouples...
« Reply #22 on: December 13, 2011, 06:53:16 PM »
http://www.yourhome.honeywell.com/Home/Products/Thermostats/SummaryList.htm go here first pick out your stat and download the pdf instructions for the correct model. Is this the old style round with the mercury switch & coil spring when you pull off the cover or the new all electronic style if its the new style there is a set of two switches on the back of the stat housing that can be adjusted for cycles per hour.

If your is the new style stat be careful when you pull the stat assy away from the wall plate to adjust it. they have a connector on the back for the wiring , remember its plastic not titanium  ;)

Offline Adam B.

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Re: My furnace keeps burning out thermocouples...
« Reply #23 on: December 14, 2011, 02:19:45 PM »
Thanks. I'll check that out at some point tonight. I was paying attention last night and the time between cycles seemed longer, but it was a little warmer than it was last weekend when it was cycling really fast.
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