My Intertherm furnace started to malfunction recently. By this I mean it just stopped working. Prior to this a few times over a month when it would start the process of heating in the chamber it would click over more than the usual one time before the fan comes on. The fan would come on and push out cold air. I restarted it once and it continued to work for a bit. I found keeping the thermostat lower helped the start over situation mentioned above. Then it went out again and pulled the code listed as #3- pressure switch closed with inverter off. What is the matter?

Either the pressure switch is stuck or the board is bad. To test, pull one wire off the pressure switch & start the furnace. Wait about 5-10 seconds & put the wire back on. If the furnace goes through the rest of it's ignition sequence, the switch is bad. If it does not and gives you the 3 code again, the most likely problem is a bad control board.

Thx Grady I will try it. Awesome info and I like the tag line. I have the bumper sticker.

Let me know how things go.
Just curious, where do you live?