I have a Bryant Plus 80 that stopped working - the gas burners weren't igniting. Brought in a repairman who replaced the pressure switch ($350) and... it didn't work. Now he's thinking it's the circuit board's relay switch which isn't working which means we need a new circuit board ($800 more). The circuit board gives a error code "23" which relates to the pressure switch not working so now I'm confused.

I can start the furnace manually by disconnecting the hose to the pressure switch until the fan cycles down and replacing it. That works until the thermostat tells it to shut off and then it won't refire.

Here's my question: How do I know it's the circuit board? He seems to be certain - but then again, he was certain about the pressure switch. I'm out of my league here. :-(