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ohman 12-31-2011 10:44 AM

Gas furnace overheating problem with two solutions - which one is better??
 
Hi there, thanks for reading this thread.

We have a 15 years old Day&Night gas furnace that has been working fine until now. For some reasons over the past two weeks, the unit (furnace) became so hot that it would just shut down by itself, which we will have to then go to the basement and "reset" it for it to come back to work. Very annoying.

We called up two professionals to give us a quote for repairing. One is a very experienced general contractor, but he is not specialized in HVAC. The other is a HVAC professional. After inspection, they came up with two different solutions/ideas. The HVAC professional suggested that we should get the "inducer fan" replaced as the motor is quite old and might not be as efficient and effective as before. If after replacing the "inducer fan" the problem still does not go away, then we should consider to replace the current 8" Flue Vent to 10".

The general contractor suggested that we should just go ahead and replace the 8" Flue Vent to 10".

http://homerepair.about.com/od/heati...ectr_ign_5.htm

Thoughts or comments about these two different approaches? Based on your experience, which solution would have better chances to solve the unit overheating problem once and for all? Which one would be more economical? It seems that for either solution, they will want to charge around US$350 - 400 (parts + labor).

Thanks!

joecaption 12-31-2011 10:54 AM

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.

AandPDan 12-31-2011 10:55 AM

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.

harleyrider 12-31-2011 11:02 AM

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.

yuri 12-31-2011 11:06 AM

1 Attachment(s)
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.

beenthere 12-31-2011 11:33 AM

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.

plummen 12-31-2011 12:00 PM

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 :)

biggles 12-31-2011 02:57 PM

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?

REP 12-31-2011 04:39 PM

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.

ben's plumbing 12-31-2011 05:31 PM

Quote:

Originally Posted by REP (Post 808497)
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.

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

cleveman 12-31-2011 11:18 PM

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.

ohman 01-10-2012 03:00 AM

Quote:

Originally Posted by REP (Post 808497)
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.

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!

cleveman 01-10-2012 05:02 AM

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.

harleyrider 01-10-2012 08:40 AM

Quote:

Originally Posted by ohman (Post 818175)
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!

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?

ohman 01-31-2012 12:56 PM

Quote:

Originally Posted by cleveman (Post 818192)
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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