# Gas furnace overheating problem with two solutions - which one is better??



## joecaption (Nov 30, 2011)

If it's worked fine for this long without a 10" flue something had to have changed to cause the problum.
Take your info from a HVAC contractor not a GC.


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## AandPDan (Mar 27, 2011)

Not an HVAC tech but something sounds odd.

Get another HVAC tech in. One that will troubleshoot and not "assume."

If the furnace is lighting and getting hot enough to shut down, then the inducer motor should be working. If it wasn't then there should be a pressure switch to shut down the furnace or even prevent it from lighting.

I can't see any reason, short of a clogged vent, why you would even consider increasing the size when it had been working for 15 years. 

Is the vent clean? Is the blower motor running? The one that blows the air through the duct work? Is the filter clean? These will easily cause an overheat.

Is there a fault code showing.

Good luck.


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## harleyrider (Feb 20, 2007)

NEITHER............if your furnace is going off on the high limit, it is because the heat being made in the heat exchanger is not getting carried away fast enough to keep a steady temperature in the heat exchanger, causing it to rise above the "limit" of the limit and trip it.....shuting down the furnace. I would suspect a couple different things.........first and most obvious, is the filter clean? Second I would be suspect of the blower and or capacitor being or going bad. As the blower runs its building heat inside the motor......if it gets to hot it will shut it self down, leaving the furnace to heat up and go off on the high limit......after they both cool back down then they run again.


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## yuri (Nov 29, 2008)

look in the viewing window in the lower door and get the error code when it acts up. CAREFULLY count the slow and fast flashes and read the error code diagram for more info and report back . easy to get the 2 mixed up. should have a code for high limit open vs pressure switch code which would indicate a venting problem.


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## beenthere (Oct 11, 2008)

Please post a pic of your actual furnace. And also show us what reset button your pushing. It could well be that you are resetting a roll out switch. Which could mean that your furnce has a cracked or burnt through heat exchange. And replacing the inducer and or flue/chimney pipe is nothing more then a waste of money.


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## plummen (Jan 10, 2010)

Im not sure why the size of the chimney would affect a furnace running after so many years unless you have something blocking the chimney,the pressure switch from inducer motor should have shut that down not a limit switch.
Does your furnace have an A-coil on top for central air unit?
Have you been been keeping filter clean/changed?
A dirty filter can cause lots of issues over time including clogged squirrel cage or plugged up A-coil,either of which could contribute to higher operating temps.
Id also check the blower motor itself to make sure its not getting tired and slowing down after running a while,this could also cause higher temps


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## biggles (Jan 1, 2008)

do you have AC with a coil is it clean above the heat exchanger....the rounds on the main supply fan are they clean....with fan running does the fan access door suck air bigtime...in the house does the return grill hold a sheet of the SF Examiner up with no problem....something is going on with the air over the heat exchanger not up and thru it on the burnt gas side....did the AC ice up t all during the summer?did the air on the register change in 2 weeks should be Lo Med/LO for heating...test this just at the stat put the FAN/ON no system... is it the same as it was in the summer?


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## REP (Jul 24, 2011)

Something is very wrong with this situation.
First ande most obivious is that if the 8" flue worked for 15 years,why would anyone that knows anything suggest replacing it?
Second what size furnace is this that requires an 8" flue?Most indused draft furnaces I've worked on need a 4" flue,maybe a 5" flue.
Third , you said they were both in your house and seen the shutdown and the HVAC guy didn't know if the induser motor was any good.What happened did he leave his meters in the truck.
Fourth ,if its going out on limit it could be a weak limit.
Fifth ,it could as already mentioned be a bad blower motor(the one UNDER the furnace) or capsitor yet nobody mentioned that possibility while they were there.
It could be a plugged heat exchanger causing it to over heat.
What you have to do is find a REAL HVAC company to troubleshoot the furnace and find out what is wrong.I could make a wild guess from here but thats all it would be.
What you have is a dangerous situation and it needs to be treated as a big problem not merely an inconvenious.


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## ben's plumbing (Oct 6, 2011)

REP said:


> Something is very wrong with this situation.
> First ande most obivious is that if the 8" flue worked for 15 years,why would anyone that knows anything suggest replacing it?
> Second what size furnace is this that requires an 8" flue?Most indused draft furnaces I've worked on need a 4" flue,maybe a 5" flue.
> Third , you said they were both in your house and seen the shutdown and the HVAC guy didn't know if the induser motor was any good.What happened did he leave his meters in the truck.
> ...


 sixth you go boy can't hold you down:laughing::laughing::laughing::laughing: i agree check all of the above....


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## cleveman (Dec 17, 2011)

I'm going with the gasket where the inducer motor mounts on. Heat is coming out there and building up. Try leaving the cover off and see if that solves the problem. If so, then take off the inducer motor and replace the gasket.


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## ohman (Jun 23, 2009)

REP said:


> Something is very wrong with this situation.
> First ande most obivious is that if the 8" flue worked for 15 years,why would anyone that knows anything suggest replacing it?
> Second what size furnace is this that requires an 8" flue?Most indused draft furnaces I've worked on need a 4" flue,maybe a 5" flue.
> Third , you said they were both in your house and seen the shutdown and the HVAC guy didn't know if the induser motor was any good.What happened did he leave his meters in the truck.
> ...


Thanks so much for your feedback and comments, I really appreciate it.
The HVAC guy did use his meters to measure it and noticed that the "temperature limit switch" and the "pressure switch" was a bit off, so he replaced both. However, it was a wrong guess. Although now the gas furnace is sort of working again, but when the weather is really cold that we are forced to keep the gas furnace on for the whole day, the furnace will eventually shut down by itself due to overheat.

My conclusion is that this HVAC guy is not "professional enough" and always use second guess, so I think we will be hiring another "better" HVAC professional that we know of (very hard to make an appointment with him, too popular and never return phone calls)...

Just a quick FYI in case anyone is interested, the furnace is "Day & Night" and the Model# is 383KAV042091, Series G, by BDP Company of Indianapolis.

By the way, how would a *heat exchanger* get plugged?? I'm thinking that it might be the gasket too. How do people trouble shoot the gasket though?? Just curious. Thanks!


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## cleveman (Dec 17, 2011)

multiple tennis balls dropped into heat runs, then dropping into the heat exchanger. Is there AC on this unit? Probably a labrador retriever to blame.


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## harleyrider (Feb 20, 2007)

ohman said:


> Thanks so much for your feedback and comments, I really appreciate it.
> The HVAC guy did use his meters to measure it and noticed that the "temperature limit switch" and the "pressure switch" was a bit off, so he replaced both. However, it was a wrong guess. Although now the gas furnace is sort of working again, but when the weather is really cold that we are forced to keep the gas furnace on for the whole day, the furnace will eventually shut down by itself due to overheat.
> 
> My conclusion is that this HVAC guy is not "professional enough" and always use second guess, so I think we will be hiring another "better" HVAC professional that we know of (very hard to make an appointment with him, too popular and never return phone calls)...
> ...


 Your furnace is made by Carrier corp.Its a mid-efficiency unit.I would not think that the heat exchanger would be plugged it would be very rare to have this happen.Now if you are not good at keeping the filter changed, then the evaporator coil could be plugged.How are you determining that the unit is shutting down by over heating? are you reading a fault code off the main board?


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## ohman (Jun 23, 2009)

cleveman said:


> multiple tennis balls dropped into heat runs, then dropping into the heat exchanger. Is there AC on this unit? Probably a labrador retriever to blame.


No, there is NO AC on this unit.


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## ohman (Jun 23, 2009)

harleyrider said:


> Your furnace is made by Carrier corp.Its a mid-efficiency unit.I would not think that the heat exchanger would be plugged it would be very rare to have this happen.Now if you are not good at keeping the filter changed, then the evaporator coil could be plugged.How are you determining that the unit is shutting down by over heating? are you reading a fault code off the main board?


Yes we have not been constantly changing the filter as I believe that we have washable furnace filter installed and we do wash it. Can you DIY clean the evaporator coil? I found this YouTube video but that one seems to be a furnace in a commercial building. We know that it's shutting down by over heating because we hired two HVAC professionals to take a look and both said that the problem was overheating. Currently we have spent around $500 to replace the limit switch, the pressure switch, and the temperature sensor. Although replacing these parts did help (it happens less frequent now), but still maybe once a month the furnace will shut down by itself due to overheating (used to be once a week). Thanks!


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## ohman (Jun 23, 2009)

Oh by the way, we are no longer considering the general contractor's idea to replace the current 8" Flue Vent to 10". We hired two HVAC professionals now, one suggested to replace the furnace with a high efficiency one (labor + part quoted US$2600), and the other one suggested to replace the existing terra cotta flue and install the new double wall flue and quoted $3300 (the current set up with terra cotta flue was inherited from a old old furnace that we had before, which was not even 80% efficiency furnace).

For this new development (high efficiency furnace) I have started another thread, please see here.


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## bobinphx (Nov 25, 2011)

since you mentioned a washable filter, you get my take on them!!! They are junk unless you take apart the frame and clean each peice of them. Then put them all back together, once a month or more, depending on your houseold (ie dogs, cats, living in the desert!!! LOL) They tend to get clogged up in the inter layers. 

Try this experiment, Go get a cheap fiberglass filter, put it in for 1 week. if the problem goes away, dump that washable filter. 

I would further suggest that if your filter area can handle it, try for a 4 inch media filter. There are a couple of places on the internet that sell drop in systems if your return filter is only sized for 1 inch filters. I dont like the hardware store 1 inch pleated filters, as they seem to be very restrictive... your mileage may vary!!!!

here is a sample of the filter type I am talking about. http://www.hayneedle.com/sale/furna...sku=QFI081-4&gclid=CNnO9c6Qgq4CFaYaQgodCznX2Q


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## hvac5646 (May 1, 2011)

bobinphx said:


> since you mentioned a washable filter, you get my take on them!!! They are junk unless you take apart the frame and clean each peice of them. Then put them all back together, once a month or more, depending on your houseold (ie dogs, cats, living in the desert!!! LOL) They tend to get clogged up in the inter layers.
> 
> Try this experiment, Go get a cheap fiberglass filter, put it in for 1 week. if the problem goes away, dump that washable filter.
> 
> ...


This is spam!


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## harleyrider (Feb 20, 2007)

hvac5646 said:


> This is spam!


 why.....?


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## bobinphx (Nov 25, 2011)

sorry about that, I did not intend to spam. I had a really hard time finding a media filter that would fit in a standard return filter grill. a filter like this was my answer and I thought I would share it. How can I show things that I find on the internet in the future????? Again, I dont want to spam. Thank you.


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## hvac5646 (May 1, 2011)

harleyrider said:


> why.....?


Cause it is:laughing:


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## yuri (Nov 29, 2008)

Bob.

No spam for me. Norton blocks every bit of it 4 me. Perhaps his scanner is letting something thru like pop ups. Keep posting, not everyone has a good pop up blocker. A bit of advertising is allowed here as long as it does not lead to a bunch of other commercial sites and overload the server or promote the posters biz.


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## hvac5646 (May 1, 2011)

They got Norton in Canada:whistling2:?


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## yuri (Nov 29, 2008)

Yep. mail delivery too. not that artificial e-mail stuff.:laughing:


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## Marty S. (Oct 31, 2009)

bobinphx said:


> sorry about that, I did not intend to spam. I had a really hard time finding a media filter that would fit in a standard return filter grill. a filter like this was my answer and I thought I would share it. How can I show things that I find on the internet in the future????? Again, I dont want to spam. Thank you.


You're fine bob. A link to the company you own or work for is spam. Posting examples from the net isn't.


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## beenthere (Oct 11, 2008)

From the rules:

 Users may link to commercial or informational sites as long as you have no vested interest in doing so. Example, someone posts a link to a new tool that they are using or to a leads service they have had success with. We are just trying to stop SELF PROMOTION and not valid discussions. We reserve the right to delete any message that we are unsure of its intentions.


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## mystar (Mar 10, 2012)

*Carrier Furnace series 140*

,,,,,,,


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## heatingman (Mar 17, 2012)

harleyrider said:


> NEITHER............if your furnace is going off on the high limit, it is because the heat being made in the heat exchanger is not getting carried away fast enough to keep a steady temperature in the heat exchanger, causing it to rise above the "limit" of the limit and trip it.....shuting down the furnace. I would suspect a couple different things.........first and most obvious, is the filter clean? Second I would be suspect of the blower and or capacitor being or going bad. As the blower runs its building heat inside the motor......if it gets to hot it will shut it self down, leaving the furnace to heat up and go off on the high limit......after they both cool back down then they run again.


i agree with harleyrider but if you have a/c i would check the coil to c if its dirty that can also cause over heating


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