Goodman Furnace runs perfect until weather gets 25 or lower

Problems related to residential installations.

Goodman Furnace runs perfect until weather gets 25 or lower

Postby Brad1 » Sun Jan 15, 2012 2:29 am

I have a model GMNT080-4 condensing gas furnace.

When the weather outside is about 25 degrees and higher the heater kicks in and heats to thermostat setting perfectly.

When the outside temp gets colder than about 25 degrees the heater kicks in but will not heat to the thermostat setting. Instead of heating to 74 degrees thermostat setting, the heater will only kick in at about 62 degrees and never get the home above 67 degrees.

I want to know how to get this heater to keep our home at thermostat setting when it gets very cold outside.

The control board was replaced and entire furnace checked by a professional with no change in furnace issue.
Brad1
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- Goodman Furnace runs perfect until weather gets 25 or lo

Postby Brad1 » Sun Jan 15, 2012 12:53 pm

Here's exactly what the tech wrote on his - "Diagnose furnace problem on Goodman 90+ furnace. Furnace fails to stay light off running for a period of time. Need to replace PC board B18099-13."

I replaced the board and it stills does the same thing.
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- Goodman Furnace runs perfect until weather gets 25 or lo

Postby Freon » Sun Jan 15, 2012 2:40 pm

"Instead of heating to 74 degrees thermostat setting, the heater will only kick in at about 62 degrees and never get the home above 67 degrees." Does this same behavior happen when it's 25 or above? When it's 25 or above does the call for heat happen at 74 (thermostat setting) or 62? If heating starts at 62 even though the thermostat is set for 74, then something's wrong with the thermostat.

When it's below 25 and the furnace doesn't fully heat the house, does the main blower continue to circulate air even though it's cold due to no combustion happening?

Is the furnace located in a place that will be colder when it's colder outside, like an unheated basement?

If you can watch the furnace run on a 20 degree day look and see if after the fire goes out there is an attempt to re-light, possibly after a minute or so. When the fire goes out, does the inducer motor stop also?

If the temperature is affecting the inducer assembly then the furnace should completely stop... no air circulating in the house, no re-light attempts. If the furnace is going off because of overheating, then the main blower should stay on and there should be a re-light attempt after the heat exchanger cools down... maybe a minute or 2. You need to observe carefully to know what may be the problem. If it's very cold and you directly jumper, TEMPORARILY and with POWER OFF, the R and W terminals (bypass the thermostat) and it runs well, then it's the thermostat.
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- Goodman Furnace runs perfect until weather gets 25 or lo

Postby derrold_d » Fri Jan 20, 2012 2:14 am

i would also check fluing sounds like it maybe icing up and stopping the intake or exhaust air from geting to/from furnace. check termination of flues most likly side wall termination is on backwards or somthing.
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- Goodman Furnace runs perfect until weather gets 25 or lo

Postby how » Fri Jan 20, 2012 8:48 pm

It could be so many things with the info you've given. Even a sluggish condensate drain could do it. You should have a led diagnostic light blinking on your furnace somewhere if your thermostat is continuously calling for heat and the burners are cycling on & off.
Look for it through the grill on the furnace door or an inspection port. The legend to explain it will probably be on one of the doors. Let us know what you find.
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