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Douglas
Douglas, HVAC Technician
Category: HVAC
Satisfied Customers: 3089
Experience:  Manufacture Rep for Major Brand, Technical Trainer, NATE
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How do I fix pressure switch on my furnace that is stuck open?

Resolved Question:

The pressure switch is stuck open on my furnace, how do I get that to come back on?

Submitted: 6 years ago.
Category: HVAC
Expert:  Douglas replied 6 years ago.

Douglas :

First you need to cycle the power. On a new call for heat, does the inducer motor start?

JACUSTOMER-py6uoz5j- :

No

Douglas :

That is why the pressure switch is open.

Is the inducer motor hot to the touch?

JACUSTOMER-py6uoz5j- :

No

Douglas :

Do you have a volt meter?

JACUSTOMER-py6uoz5j- :

No

Douglas :

Ok... In a nutshell, the pressure switch is a verification that the inducer (combustion fan) is on and that the vent is clear. If the vent is restricted or the inducer motor does not come on, the pressure switch will not work. If the motor were hot, it may be that the motor is bad, being cool, I would want to know if it had voltage so I knew where to go next.

The pressure switch is the disk shaped device with a rubber hose leading to the inducer assembly. You may want to take the hose off and blow the hose out and then blow and draw gently on the pressure switch to see if it clicks. If its stuck closed, it will not allow the inducer to start.

JACUSTOMER-py6uoz5j- :

There are two disc shaped devices on the furnace, one on the left and one on the right, which one do I check?

Douglas :

Both

JACUSTOMER-py6uoz5j- :

Ok,

Blew out both hoses and still getting three flashes, stating the pressure switch is still stuck open

Douglas :

It will be. Did you turn the power off and back on at the furnace? (if there is not a switch, just pop the blower door off and put it back on.

Don't turn it off at the thermostat, cycle the power at the furnace

JACUSTOMER-py6uoz5j- :

Ok, we are putting the panelling front on the furnace. I will cycle at the furnace, be right back.

Put the door back on, turned furnace switch on, and still have 3 flashes saying pressure switch is stuck open. Furnace still did not come on

Douglas :

Give it a few minutes... May be a time delay in your thermostat.

JACUSTOMER-py6uoz5j- :

Could there be a reset switch I am missing?

Douglas :

No

JACUSTOMER-py6uoz5j- :

Do you have any other suggestions, the light continues to flash?

Douglas :

Well.... Can you find someone with a meter? As of right now, it is telling us what we already know. The inducer is not running and therefore the switch is not closing. How many wires go to that pressure switch?

JACUSTOMER-py6uoz5j- :

I do not know where the pressure switch is. Right now I cannot find anyone with a meter.

Douglas :

It was the disk shaped thing connected to the hose you blew out...

JACUSTOMER-py6uoz5j- :

Ok, there are two of them. Do I check both of them, and can I check them without a voltage meter?

Douglas :

Disconnect one wire from each of them and see if the furnace inducer starts... One at a time.

JACUSTOMER-py6uoz5j- :

Ok , The disk on the left has two grey wires, and the disc on the right has yellow and orange wire and they are plastic and will I get a shock by pulling one of the wires off?

Douglas :

Turn the power off, remove the wire, turn the power back on, just make sure the wire terminal is not touching anything.

JACUSTOMER-py6uoz5j- :

Ok, its done

Douglas :

Did anything happen?

JACUSTOMER-py6uoz5j- :

No, still nothing

Douglas :

Well..... Then its one of two things and without a meter. Either the inducer motor is bad or the board is. I would invest in a volt meter or just call someone to determine which it is. But that inducer motor needs to be running which would make the pressure switch close. I don't know if the motor is bad or the board that sends the voltage to the motor.

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