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have you verified the pressure switch closes without you assisting it?
first lets do a test..
Get a paper clip..turn power off to furnace...remove the 2 wires on the pressure switch and hold apart.
AFTER the exhaust starts to run, slide one end of paper clip into pressure switch wire and also the other wire. This connects the 2 wires and mimics a closed pressure switch.
Tell me igniot starts to function.
This means it is indeed not closing..but it may not be the switch.
Unhook bypass now...remove rubber tube from switch and use paper clip to poke out the fitting it is attached to, check vent pipe for any obstructions.
This means something is blocking the air flow or the switch is bad.
BUT this is a safety that really should not be bypassed. Find out what you can about blockage first.
the biggest reasons for air not reaching pressure switch..
small rubber tube is cracked
fitting tube attaches to is plugged
vent pipe or intake pipe plugged with leaves or nest
water drain (if 90%) is plugged
Pretty much anything that can stop air from getting to the switch.
Terrific....that barbed fitting is a very common spot. Thanks for the hands on !