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Sounds like the induced draft fan is turning on and it needs proof of flow for it to go to the next step. Clean the pressure switch leads which are little rbber hoses that run from switch to flue of furnace, be sure to clean the ports they attach too
Hi Rick, thanks for the quick response ... can you help me locate the pressure switch leads?
Here is what they look like
If it's the tiny switch on the side of the black circular case connected to the white PVC hose - I cleaned the leads as per your instructions. The problem remains :-(
The 2 flashing red lights indicate it is indeed a pressure switch problem.
The question is: did I clean the right leads?
I have no 'horses' around my furnace :) but I did clean the hoses. I took them out, blew air into them and put them back. Still not working.
3 red lights - stuck open pressure switch. What should I do?
I've cleaned all hoses and ports.
The rubber hoes if not clean will not senses air flow check again if hoses are free of any debris and the barbed ports also , then you can lightly blow and suck the hose and listen for slight clicking
Didn't work so I've made an appointment with a local HVAC technician.