Furnace won't turn back on after lowering the temperature, what to check?

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While you are waiting, you may wish to go to YouTube and watch the videos there by grayfurnaceman. He has a series of HVAC troubleshooting videos that are clear and easily understood by anyone with a little DIY experience. To diagnose, you may want to buy a digital multimeter. Harbor freight has them for less than $15.
 
Very difficult to do any diagnosing without a VOM .

I have a Fluke on the truck , but I have one of the HF meters at home .

Wyr
God bless
 
One more simple thing to check... do you have snow buildup high enough to be near the exhaust pipe of the furnace? If so, clear that away so there is no back pressure.

To explain, I have a setback thermostat in my house which goes down to 60 degrees each evening, and back up to 70 in the morning. One time, we had a big overnight snowstorm, and the snow drifted against the house, high enough to partially block my exhaust pipe. As a result, the next morning, the furnace would not fire up. When it tried to light, the inducer motor would start (pushes air out the exhaust pipe to make sure it is clear), but the pressure switch would not close because the exhaust pipe was partially blocked. Therefore, the furnace would not fire up. Once I cleared the snow, everything went back to working properly.

If I had not setback the thermostat. The heat would likely have been running through the night, and melting the snow as it piled up. Since the heater never went on thru the night, the snow piled up.
 
Got the new ignitor.
Installed it and turned it on.
Same thing as before, fan comes on but no fire.
That means I broke a perfectly working ignitor. :(

Red LED blinks 3 times.
What does that mean?
 
jeffmattero76 said:
While you are waiting, you may wish to go to YouTube and watch the videos there by grayfurnaceman. He has a series of HVAC troubleshooting videos that are clear and easily understood by anyone with a little DIY experience. To diagnose, you may want to buy a digital multimeter. Harbor freight has them for less than $15.
Click to expand...
Thanks for reply.
I think I have half a dozen multimeters, 3 of them are HF.
Led is blinking 3 times.
Fan turns on for few minutes and shuts off due to no heat I think.
 
Ok the error code is Pressure Switch Stuck Open.
It's only 5 years old so I doubt switch is the issue.
There's a lot of white dust like ash so maybe it's dirty.
It may be the dirt under the motor than the switch.
How do I open the motor to see if there's dirt build up around the tube?
 
If the pressure switch is stuck open, it means one of two things... either your exhaust is blocked, or the switch is bad.

Check the pipe where it exits to the outside to see if anything is blocking it, even if only partially. It could be ice, a rodent, leaves, etc. You may want to hook up a shop vac to the exhaust pipe and try to suck any obstructions through. Once you have done that, try to light it again, after turning the power switch off for a few seconds, and then back on. If it still doesn't fire up, look at your pressure switch, at the top right of your upper compartment. Take the rubber hose off of the furnace (not off of the switch), and blow into it and suck through it. As you do that, you should hear a slight click, which tells you that the pressure switch is working. If you don't hear that click, your pressure switch may be bad.
 
Okay guys. I got it working but have a question.

I checked the hose for any crack and it was perfectly fine.
Pulled hose out from inducer.
I straightened a big paper clip and cleaned the tube canal on the inducer all the way through, wiggled it around.
Next I checked the pressure switch by blowing on the tube, no click, no sound.
I'm not sure how hard I was supposed to blow but no click no matter how hard I blew.
I thought it was blocked/clogged there and inserted paper clip into the pressure switch itself, not too far but until I felt resistance.

I plugged back everything and voila, it works. My inducer motor probably is dirty.
I'll clean it before next cold season.
But I was concerned if I poked in the switch and closed the switch permanently.
So I pulled the cables out and tested the switch with a multi-meter. It was open or read 1.

full


I turned the gas off and turned the furnace on with the multi-meter still connected.
Inducer started running and after few seconds, multi-meter reading changed from 1 to some random number and then settled at 001.
When I turned the furnace off, it went back to 1.
Does that mean the switch is fine and I don't have to worry?
I can replace the switch if you guys think it's not safe. They are cheap.

Here's the video of multi-meter from open to close.
I started the video little late so it goes from open (1) to close quickly.
It goes back to 1 at the end when I turned the furnace off.



I again checked for click sound on the switch by blowing on the tube and still no click, no sound even when it's working and multi-meter shows it's opening and closing.
Is it very faint sound?

Thank you
 
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It appears that your meter is set to Diode Mode. You are not checking a diode. Switch to the 200 ohm range. With the probes attached to the pressure switch contacts, the meter should read "OL" or similar. When the switch closes, the meter should read "0" or possibly "1".
 
I can't tell what you have the meter set on. I would suggest setting it to measure continuity. Most meters have a tone when there is continuity. It would be in the segment of the meter that measures Ohms (symbol looks like a horseshoe). With the meter in that position, touch the two probes together. You should hear a tone or see a zero. That shows continuity. Then, with the power off, put the probes on the pressure switch, and it should show a 1 and will not beep. Then turn on the furnace. If the pressure switch is working correctly, you will show continuity when the switch closes. That signals the gas valve to open. When the furnace goes off, the switch should be open, and not show continuity.
 
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