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· Registered
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Discussion Starter · #1 ·
I have a furnace(p3urc20n09501e) that is suffering from lack of ignition. I have traced the problem to a likely faulty pressure switch by:
-. Inducer motor runs, blower runs, but pilot/heating element never triggers, followed by 3 blinking LED that manual describes as unable to close pressure switch.
-. Putting hand against inlet air duct outside can sometimes trigger ignition. (no longer seems to work)
-. Slight movements on pressure switch wiring can sometimes trigger ignition.

This switch, 024-27634-000, has two barbed connections. One to the burn box and one to the inducer motor. I believe tripping based on pressure differential.
I looked for a replacement switch, but a vendor recommended one is a single port switch.

My question is in multiple parts:
1. Does swapping switch make sense? Any other causes I should be looking into?
2. How to install the new switch? Install the single-ported one and crimp the unconnected hose to the burn box?

Thanks for any advice


· Hvac Pro
25,116 Posts
You MUST get the dual port one as it needs to measure differential pressure. Very dangerous to not use the proper one.

The proper way to check is to have a dual port manometer installed across the hoses and see how much draft in inches WC ( kinda looks like .65 on the blue label ) you have there.

If it is .65 to approx .95 then you have proper draft and the switch may be faulty.

Take the hoses off and poke the port thru where they attach to the furnace (NOT the switch itself ) with a small drill bit or nail. Could be debris or scale inside.

Check your intake pipe and exhaust pipe outside for debris inside them. Spider webs and leaves or wasp nest have been found there.
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