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BillyHvac, Journeyman HVAC Tech
Category: HVAC
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Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I have a York Diamond 80. 3 blinking red lights pressure switch

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I have a York Diamond 80. 3 blinking red lights "pressure switch stuck open". Exhaust fan is running. With everything off, removed hose at switch, blew into and sucked - heard switch open and close. In past have had to replace the igniter (twice thus far, over the course of around 8 years) - it seems to be fine though, reading 40 ohms. Any ideas?

have you verified the pressure switch closes without you assisting it?



Customer: replied 5 years ago.
i have not. How would I go about doing that?

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.

Customer: replied 5 years ago.
ok, give me a few minutes to complete.... brb
standing by..
Customer: replied 5 years ago.
that did the trick, it fired up..... how long can i keep it bypassed? Just want to get some heat going for a bit, then i'll shut it off. Also, is that a part i can pick up easy enough locally?

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.



Customer: replied 5 years ago.
Yeah, i was wondering about the air flow. While it is running, when I remove the hose, shouldn't there be air flowing through the tube? Or is that what you are referring to the vent pipe (where the hose attaches on the other end)? I'll give what you suggested a try. Be back in a few minutes.

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.



Customer: replied 5 years ago.
Ok, after poking the switch port with the paper clip, then the port from the other end, and hooking everything back up it works like a champ.... must have dislodged something


Terrific....that barbed fitting is a very common spot. Thanks for the hands on !



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