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Furnace just started shutting down before it reaches temp.

Customer Question
Furnace just started shutting...

Furnace just started shutting down before it reaches temp.

Contractor's Assistant: Did you check the furnace's filters?

Yes they have been changed

Contractor's Assistant: Do you plan on doing the work yourself?

Not sure how old the furnace is. it is a comfort air model and is 90%

Contractor's Assistant: Anything else we should know to help you best?

Not sure.

Submitted: 7 months ago.Category: HVAC
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Answered in 52 minutes by:
12/20/2017
HVAC Technician: airheatman, HVAC Technician replied 7 months ago
airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 9,346
Experience: Furnace, A/C and heat pump specialist.
Verified

Can you look inside the burner compartment on label on side panel and get me the model on your furnace? Then look in blower compartment and see if there is an error light blinking that will guide us in determining what is failing with the furnace.)Not if no peep hole and you have to remove blower panel to see control board, it will be necessary to hold door switch in to have power to board)

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Customer reply replied 7 months ago
GLUA120-E5A Comfort Air 2006
No code flashing
This only happens when program goes from 60 to 70 when outside temp is below 30.
HVAC Technician: airheatman, HVAC Technician replied 7 months ago

If no error code, it may be a thermostat issue.What thermostat do you have and does furnace work with a heat pump as auxilliary heat or independantly?

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Customer reply replied 7 months ago
White Rogers programmable. Stand alone NG unit. Everything working fine today. Issues last week through yesterday morning when weather was much colder. Thermostat seems to be fine.
HVAC Technician: airheatman, HVAC Technician replied 7 months ago

OK the reason I asked about thermostat is some of todays digital thermostat have settings which can control weather furnace operates or heat pump operates depending on outdoor temp.

Since it is a stand alone furnace the issue is going to most likely be with the furnace itself, but to troubleshoot, we will have to be in "non working" mode as you can not fix what is not broke as they say.

I suspect when it fails, there IS an error code.The two most likely issues are going to be a pressure switch or a limit switch.

If furnace fails to operate and the board does not give an error code, the board itself is failing us.

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Customer reply replied 7 months ago
I will need to wait until the next cold morning when the furnace won't reach temp with the program calling to bring the temp to 70. Then I will check again for an error code. One more thing that may help you is when the furnace shut off I was able to get it to restart just by setting the stat down to 1° under room temp and then after click turn it back above. Or I can turn stat off and back to heat. Seems strange to me.
HVAC Technician: airheatman, HVAC Technician replied 7 months ago

That sounds like a thermostat issue.If it was furnace, you would actually need to kill power to furnace to reset. I would go ahead and replace thermostat and see if that doesn't solve the problem honestly.

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Customer reply replied 7 months ago
Can I bypass the stat? If the stat is what is bad then it should not shut down with a jumper on it. Am I correct in assuming that?
HVAC Technician: airheatman, HVAC Technician replied 7 months ago

THat is absolutely correct. The reason I say I now suspect it to be stat is that you say lowering temp and re raising makes it come on

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HVAC Technician: airheatman, HVAC Technician replied 7 months ago

If issue were with a pressure switch, limit or something in furnace, just messing with tstat would have no effect

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Customer reply replied 7 months ago
Although I have not changed anything yet, the issue has not occured again.
HVAC Technician: airheatman, HVAC Technician replied 7 months ago

Just keep an eye on it and you have further issues we will go from here.

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