Gas Furnace does not see closed pressure switch
#1
10-09-22, 01:25 PM
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Gas Furnace does not see closed pressure switch
Hello guys,
I have a gas furnace, and when I turned it on initially, it gave me a two blink code specifying that the pressure switches stuck closed.
I’ve tested everything, including the switch with a multimeter, checked the hose, check the wiring from the switch all the way back to the control board and everything seems to be working as it should be, but the second I set the thermostat to heat. It gives me that two blink code.
I verified that the vent outside is free of obstruction and I don’t see anything in the intake port on the roof.
I went as far as to replace the switch, and it still is doing the exact same thing.
I do hear the switch audibly click when I start the furnace up.
The only thing left that I can think of is the control board, but is there anyway to verify this that you guys are aware of?
Thanks for the help and I apologize if I am asking a commonly asked question, but I’ve done 1 million searches, and I cannot find the resolution.
I have a gas furnace, and when I turned it on initially, it gave me a two blink code specifying that the pressure switches stuck closed.
I’ve tested everything, including the switch with a multimeter, checked the hose, check the wiring from the switch all the way back to the control board and everything seems to be working as it should be, but the second I set the thermostat to heat. It gives me that two blink code.
I verified that the vent outside is free of obstruction and I don’t see anything in the intake port on the roof.
I went as far as to replace the switch, and it still is doing the exact same thing.
I do hear the switch audibly click when I start the furnace up.
The only thing left that I can think of is the control board, but is there anyway to verify this that you guys are aware of?
Thanks for the help and I apologize if I am asking a commonly asked question, but I’ve done 1 million searches, and I cannot find the resolution.
#2
10-09-22, 02:31 PM
Group Moderator
Welcome to the forums.
Connect a meter on the AC setting for 24v across the pressure switch.
You need to see 24vac with the furnace not running.
Do you see that ?
Connect a meter on the AC setting for 24v across the pressure switch.
You need to see 24vac with the furnace not running.
Do you see that ?
#3
10-09-22, 03:03 PM
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To confirm:
Are you saying 24v with the thermostat not calling for heat or with the power to the furnace off.
I assume you mean with no call for heat - I’m checking that now
I assume you mean with no call for heat - I’m checking that now
#4
10-09-22, 03:23 PM
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With no call for heat but it ‘running’ (fan sound but the thermostat set for no ac or heat) I get:
0.257V on each terminal (using a ground)
0.00V if I connect the probes to each terminal.
When I turn the thermostat to call for heat, it shows 28V on both terminal’s separately
0.257V on each terminal (using a ground)
0.00V if I connect the probes to each terminal.
When I turn the thermostat to call for heat, it shows 28V on both terminal’s separately
#5
10-09-22, 04:18 PM
Group Moderator
Not to ground..... across the switch.
Most furnace keep 24v on the safety loop at all time.
It sounds like yours does not. That means on a call for heat.....before the inducer runs.... you should be measuring 24v. When the inducer starts you measure 0v.
24v would mean open switch and 0v would mean closed switch.
Most furnace keep 24v on the safety loop at all time.
It sounds like yours does not. That means on a call for heat.....before the inducer runs.... you should be measuring 24v. When the inducer starts you measure 0v.
24v would mean open switch and 0v would mean closed switch.
#6
10-09-22, 04:47 PM
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From terminal to terminal I get 0v.
I do hear a motor when I first power it on. I thought that was the inducer motor?
I do hear an audible click then the furnace is powered on and the fan kicks on. This is clearly from the pressure switch.
I do hear a motor when I first power it on. I thought that was the inducer motor?
I do hear an audible click then the furnace is powered on and the fan kicks on. This is clearly from the pressure switch.
#7
10-10-22, 07:09 PM
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Tested again
current error: 2 blinks: Closed pressure switch
(only starts blinking after a call for heat)
Before call for heat: 0V across the pressure switch terminals
after call for hear: 0V across the pressure switch terminals
With the multimeter connected to a ground:
before call for heat: 28.1V from the first wire
0v on the second wire
after call for heat: 28.1V on both wires
(only starts blinking after a call for heat)
Before call for heat: 0V across the pressure switch terminals
after call for hear: 0V across the pressure switch terminals
With the multimeter connected to a ground:
before call for heat: 28.1V from the first wire
0v on the second wire
after call for heat: 28.1V on both wires
#8
10-10-22, 08:27 PM
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Possible solution
I found that the inducer motor should not be running continuously when there is no call for heat.
My inducer motor turns on right away when I turn the panel to the furnace back on.
Everything I am reading is saying that this is a control board problem.
Thoughts?
My inducer motor turns on right away when I turn the panel to the furnace back on.
Everything I am reading is saying that this is a control board problem.
Thoughts?
#10
10-13-22, 07:10 PM
Group Moderator
Thanks for letting us know how you made out.
