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Is the inducer motor running when you call for heat?
Get yourself a voltmeter and set to "volts AC" Put one probe on each side of the pressure switch terminal (on the metal portion). You should read 24 volts. Have someone turn on heat. As inducer comes up to speed, it should read "0" volts and stay there. Let me know what you find.
Then it is stuck closed for some reason because the only time it should read "0" is when the switch is closed.
Two things: the switch should not read "0" volts with no call for heat, it is a NO (normally open) switch. Secondly, I would check the other end of the pressure switch hose (not the pressure switch end) to see if that barb is partially plugged. Maybe run a small drill bit inside the barb.
If the readings you are giving me are right. sounds like the pressure switch is sticking closed with unit off, which will cause that flash code.
Can you upload a picture here of what you are talking about?
I can see part of the pressure switch, yes.
Looks like a bi metal disk. Possibly a heat sensor or fan switch.
Not part of the pressure switch, tough.
Tap on the switch, maybe you'll break it loose. But it should not read "0" volts in the heat off position.
The reason you are getting the flash code and heat won't start is because the board "checks" the switch before starting. If it finds it closed, the heat won't work and you'll get the flash code.
If it's closed with unit off, it's a bad switch. Sorry, wish it were something else.
We just did. You confirmed "0" volts with no call for heat.
You have to set meter for volts AC and touch both terminals of the switch AT THE SAME TIME. Should read 24 volts with unit off, and as inducer comes up to speed, "0" volts.
Make sure you are making contact with the metal part of the terminals. Test the meter first in a home outlet, should read 120 volts.
Based on the information you gave me, with a reading of "0" volts with unit off, this would lead me to believe the switch is bad. Try taking one lead off the switch, call for heat, and as soon as the inducer comes up to full speed, immediately push that lead back on the pressure switch. See if it runs and doesn't give you that flash code.
Then you have a bad board.