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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8172
Experience:  Furnace, A/C and heat pump specialist.
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My furnace fan kicks on after reset (or if I force heat on

Customer Question

My furnace fan kicks on after reset (or if I force heat on from thermostat) but heat never kicks in
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  airheatman replied 1 year ago.

You should get an error code on control board in blower compartment indicating what has failed.Can you check and let me know pattern of flashing?

Expert:  airheatman replied 1 year ago.

Control board is mounted on blower housing.You may have a window to peep in to see light.

Customer: replied 1 year ago.
3 red flashes
Customer: replied 1 year ago.
It is green flashes the Once the blower starts it is 3 red flashes
Expert:  airheatman replied 1 year ago.

OK this is telling us the pressure switch is not closing or staying closed.

This could be

caused by a number of problems: faulty inducer, blocked vent pipe, broken

pressure switch hose or faulty pressure switch.

Customer: replied 1 year ago.
How do you recommend I determine which? The vent pipe looks in good condition and did not see any blockage from the outside. I also don't hear any clicking on start. And although it sounds like it's burning there is no heat or light from the furnace.
Expert:  airheatman replied 1 year ago.

1.If pressure switch is open, burners should not be on.

2.First lets make sure the small vent motor is coming on.

3.If so lets try this.

Next I want you to locate the pressure switch. It will be a small round canister with a hose attaching it to the inducer housing. Remove hose from inducer housing and leave it attached to the pressure switch. Power off and back on to reset board again, Then call for heat at thermostat. Allow inducer to start then suck on the end of hose still attached to pressure switch and see if switch will close and burners ignite.

Customer: replied 1 year ago.
I hear the small click, but I dont see any ignition.
Expert:  airheatman replied 1 year ago.

OK does igniter glow after you hear the click?

Customer: replied 1 year ago.
No. I do not see anything glowing
Expert:  airheatman replied 1 year ago.

Look closely at igniter and see if there is a broken or burned spot.

Customer: replied 1 year ago.
Looks in good condition can send a picture if it helps
Expert:  airheatman replied 1 year ago.

When sucking on hose still attached to switch do you still get error code?

Customer: replied 1 year ago.
Expert:  airheatman replied 1 year ago.

D you have a meter to verify the switch contacts are closing?Either switch is bad or board is not reading it closed.

Customer: replied 1 year ago.
I do which contacts should I check.
Expert:  airheatman replied 1 year ago.

Check to see if the circuit has continuity between pins 10 and 7 on each side of the pressure switch. See below

Customer: replied 1 year ago.
The switch always seems open if if I try to close it by pulling air our
Expert:  airheatman replied 1 year ago.

Sentence did not complete. Please explain

Customer: replied 1 year ago.
I put a resistance meter across the pressure switchs two terminals after removing the wires from the two terminals. Even when sucking air from the switch I could hear a click but did not see any change in resistance between the terminals.
Expert:  airheatman replied 1 year ago.

OK looks like pressure switch is the problem You will need to replace it.