My Trane furnace stopped suddenly. Light flash 3 times. Pressure switch fault? Checked with meter and is working. Furnace runs great when hose from gas valve is unpluged from pressure switch. Also checked condensate lines they are clear. What is the problem?

Check the furnace intake to be sure it is clear. Wasp nest and other like debree can find their way inside to the intake screen at the furnace. Does the enducer seem to come up to full speed?

Eric D

Yes, inducer runs a full speed.

Did you check the inlet all the way to the screen at the furnace?

Eric D

Problem found! With temp so cold here this morning the induction pipe was plugged by a frost build up because exaust pipe is venting 6 inches away creating a lot of steam and induction pipe is sucking it right in.

Problem found! With temp so cold here this morning the induction pipe was plugged by a frost build up because exaust pipe is venting 6 inches away creating alot of steam and induction pipe is sucking it right in.
The intake to exhaust are to close to each other. Normally the exhaust should set at least a foot above the inlet for the exact reason you ran into.

Glad you found the problem,

Eric D