Goodman furnace problem

ACB2 · 01-13-2010, 11:33 AM

My Goodman GMP075-3 furnace for the second floor of my home is acting up. Here's the pattern some of the time.
Thermostat calls for heat
Inducer fan starts- sometimes stops and tries to start again, sometimes runs and the ignitor starts lighting the burners. Will run for about 2 minutes the shuts down. Sometimes it will run for however long is necessary to satisfy the thermostat, sometimes not, and will shut down before reaching temp and then the inducer may cycle on and off not igniting the burners.
I suspect a control board problem, but sometimes the unit runs just fine.
It is in my attic I have checked the exhaust pipe and pressure switch/ no obstructions and working properly. Also tstat is AOK. Any ideas?

Thanks

kennzz05 · 01-13-2010, 11:41 AM

is the condensation draining away and not freezeing up somewhere attics are the worst possible place for a condensing furnace unless of course its heated

SKIP4661 · 01-13-2010, 02:57 PM

The gmp is a standard efficiency furnace, does not condensate. Next time it fails get the number of flashes, if any, from the circuit board diagnostic light.

ACB2 · 01-13-2010, 06:17 PM

There are no flashes from the diagnostic light. It is constantly on. I think I mentioned that it does occasionally run through the cycle without a hitch, though the most noticable problem (other than lack of heat) is when the inducer fan seems to start and stop, or fail to run properly at the beginning of the cycle. It may just tick on and off for anywhere from 1 to 5 seconds before cycle failure. But no light on the board to indicate the failure.

SKIP4661 · 01-13-2010, 07:09 PM

It could be a thermostat problem. The best way to check this is to by-pass the thermostat. To do this you need to connect the white and red wires together, either at the thermostat or furnace. If when by-passed, the furnace fires and runs replace the thermostat. If it doesn't work right it could be a loose wire, high or low voltage, check the plugs and connections. It could be a board but maybe not.

ACB2 · 01-13-2010, 10:32 PM

Thanks. I have two of the same type t-stats (other is in use for the first floor furnace, and that works without problems) and I have swapped them with the same result. I will try the by-pass just to confirm though.