Goodman furnace Mod#GMNT080-4 Problem

[PDiddy1998]

The issue that I am having is the furnace will not shutoff unless the switch on the TSTAT is in the off position. The TSTAT has been changed out. Is the circuit board possibly going out?

[Admin]

Did this become a problem since the thermostat was replaced?  It's unlikely you have 2 bad thermostats.  It could be a low voltage wiring problem.  How many wires go to the thermostat?  What kind of thermostat did you install?

[PDiddy1998]

It started before the replacement of the Tstat. The original was a  white rodgers, the next was made by hunter. I thought the same thing with the voltage, but verified from the Tstat back to the furnace with all voltages good. Unless its a sporadic hit or miss situation? These things are hard to catch if thats the case. I have had a 50/50 explanation with this 2 have told me Tstat and 2 have said board.

[Admin]

Did either of the thermostats have a common wire connected?  I have seen power robbing thermostats leak voltage down W.  I have never seen it happen on a goodman though.

Is there anything else wired to W at the furnace, like a humidifier?

You could also wire the old White Rogers thermostat down at the furnace and eliminate all the wiring.  Wire only Rh and W, and see if the problem persists.  If it's not the thermostat or wiring then I would agree, the board is likely to cause intermittent problems.

To clarify, the heat stays on or just the fan?

[PDiddy1998]

The heat stays on constantly. I spoke to a tech about it and they said when he has ran into this 9 out of 10 times it was the board. It has started working recently, but it seems to be cycling off and on more frequently

[PeterT]

Turn the power off to the furnace. Pull the red wire on the tstat block now re power the furnace. If there is no call for heat jump R to W to call for heat. If you remove the jumper and the furnace shuts off there is nothing wrong with the board. Check your tstat wires, have seen them shorted out by mice chewing or a nail for a picture through the wires.