American Standard Freedom 90 Furnace - Gas valve circuit error

[vrapp]

This is a 2 stage furnace. It will not go to 2nd stage. I have watched/waited the 10 min after thermostat calls for heat, it starts to go to use 2nd stage then just goes back to 1st stage and does keep running. It then shows a flash code from the controller board = 7 -> Gas valve circuit error.
I did replace the flame censor, it made no difference. What's next? Replace the gas valve?

 

[AC Power]

The flame sensor would have prevented even the first stage from coming on. Yes, likely it's the gas valve, but I would be careful about changing that yourself. If you can't afford a gasfitter right now, save $$$, rely on single stage for now....it's just going to take longer to bring the house up to temp.

 

[vrapp]

Thanks Mr AC!
Well, I did replace the gas valve, with a shinny new one and unfortunately I get exactly the same response from the furnace. It tries to go to stage2, the flame momentarily, about 1 sec, increases, the main blower increases, then back to stage1 and the controller board LED starts flashing 7 flashes, "Gas Valve Circuit Error". You are right about stage1, it does take longer to bring house up to temp and fine if its not too cold out, but when its cold out, then it really does not keep up. The controller board seems good in all other respects. I was even able to adjust the dip switches to change the wait time from 10 min to 5 min when going from stage1 to stage2 when thermostat continues to call for heat. Is there possibly some other sensor check which is failing at the transition from stage1 to stage2?

 

[AC Power]

I don't know anything more about this. I might guess it's a combustion issue. Try opening the furnace front covers, attempt to start second stage heating, see if this changes. With the front door to the fan compartment open, your will most providing plenty extra air to the burner, which will affect the combustion. If you find the unit stay in stage 2, you've an intake air problem.

Also ensure you don't have any ice/snow build-up around the 2" plastic exhaust pipe coming out the side of your house. Sometimes, people don't see that the pipe is partially plugged, and this effects the air/fuel mixture in the furnace.