I've had no issues with this unit for years up until last week. It fires but shuts down after 10 seconds. Repeats sequence twice then triggered Air Flow fault.
I'm fairly handy and do a lot of appliance repair so I've tried all the usual suspects. Flu was a bit dirty but is clear now.
Working thru the troubleshooting flowchart I see 24VAC at the purple wire of air pressure switch at all times but I'm only getting 24 VAC on the other side of the switch when fan is on high (purge cycle) not at the lower speed it's running at ignition.
I'm replacing the air pressure switch first (after verifying vacuum hose is fine) but I'm doubtful this is the issue as the switch appears to work (continuity test) when applying vacuum manually.
Any ideas? I hate to replace the ignition control module on a whim as they're pricey.