The gas furnace will start and light the pretty blue flame but then it clicks then doesn't start the blower. The 4 flashes on the control board LED means "High Aux or Spill Limit Switch Open". I just changed the filter because it looked really dirty and I change that thing every 3 months.

Anything I can check in the meanwhile before I call someone?

This message has been edited. Last edited by: mark123, December 10, 2022 03:35 PM

From my prior experience it was usually some sort of "control board". I suspect you are looking at a service call from a HVAC repair.

I had that issue years ago. It was some solenoid switch. No idea how I figured it out but I was able to buy a new solenoid and fix it myself. I’m sure I found the answer on the web somewhere.

My gas heat/air conditioner blower combo has a separate switch that looks like a light switch on the wall. If you have that type of unit It may have been accidently turned off or tripped.

Well it runs and fires the gas but the blower never starts. The small blower that brings in the outside air and exhausts the fumes does blow and the exhaust tube gets hot but the blower to move the heat to the living area doesn't work. The limit switch does read open after running but it closes if I let the furnace cool.

Is there an overload switch on the blower motor?

Since you just changed the filter, is there some limit switch you may have bumped that's not engaged now? Perhaps a switch that's made when the filter door is completely closed correctly?

Could be a bad blower motor start capacitor. You can try giving the blower motor a "boost" and give it a spin by hand if you can access it. If it then continues going you know it's the capacitor. A $20ish dollar part and easy fix.

If you can tell us the make and model you might get more specific info. One of the HVAC guys here saved me from buying a new furnace last year as the control board on our old one went bad, and wasn't made any more, but he pointed me to a "universal" one that got it running again.

Sounds like flame sensor. It's not seeing that it's lit and turning off so it doesn't pump gas into the house. Where you see that pretty blue flame look for a sensor with a wire leading to the control board. Remove one or two screws holding it in. It will look like a piece of porcelain with metal rod coming out of it, if you see a smell heating element looking thing, that is your hot surface ignitor, put it back and grab the other thing. If one only has a single wire leading to it, that one is most likely the flame sensor.

If it's not cracked or broken then you can clean the metal portion with a green scotch Brite pad and put it back this will buy a few days to months to source a replacement. If it is cracked or broken then you're out of commission until it's replaced.



**Edit no fan at all when set to fan only means you can probably disregard everything I typed.

I tried turning the switch on the thermostat to make the blower run even with the heater off. No blowing occurred . I think it's either the blower or the capacitor.

I'll check the cap after coffee so I don't sleepily touch the leads while it's charged.

quote:

Originally posted by ubelongoutside:
If you can tell us the make and model you might get more specific info. One of the HVAC guys here saved me from buying a new furnace last year as the control board on our old one went bad, and wasn't made any more, but he pointed me to a "universal" one that got it running again.

Luxaire model G9T08012UPB13C

You have the option of burning the place to the ground and warming yourself with the flames, but that is a poor long term strategy for warmth, unless you use the insurance payout to move to Arizona.

I have oil heat and inside the furnace housing are two breakers. If I wake up in a meat locker (like this morning, when it was 50F inside), I press and hold each for 20 seconds; when I release it, the furnace restarts. If not I try the other breaker. If both don’t work, I lock myself in the bath with a space heater until the service tech shows.

My component tester reads the capacitor as a 147.8k ohms resistor. Yeah, I think it's bad.

Your symptom: Burners operate, opens high limit due to no airflow and shuts down.

Blower not operating due to one of the following:
1. Bad capacitor
2. Bad motor
3. Bad control board

Use a meter which has a capacitance setting to check the capacitor.

quote:

Originally posted by Excam_Man:
Your symptom: Burners operate, opens high limit due to no airflow and shuts down.

Blower not operating due to one of the following:
1. Bad capacitor
2. Bad motor
3. Bad control board

Use a meter which has a capacitance setting to check the capacitor.

It reads at 0uF and the component tester reads it as a 147.8k resistor. I'll replace it as soon as I get my hands on one. I'll report back.

quote:

Originally posted by Excam_Man:
Your symptom: Burners operate, opens high limit due to no airflow and shuts down.

Blower not operating due to one of the following:
1. Bad capacitor
2. Bad motor
3. Bad control board

Use a meter which has a capacitance setting to check the capacitor.

Excam man is the expert here. I had the same issue last year on my Lennox. Going frmo memory, but I think the code was a limit switch. Turned out the board was friend. I bought some limit switches and the previous owner had purchased an extra motor, so I even tried that. After using the electrical schematic and troubleshooting I narrowed it down to the board. I removed the board and saw the black on the back where something shorted out.

To make matters worse, I got a new board, installed it and had the same problem. I re-checked everything and still came back to a bad board. The furnace parts place would not swap out the board as I am not a "pro". I bought a new board anyway, and that fixed it. I was able to take the defective board back to the parts store and they gave me a refund.

I hate paying people to fix stuff if I can troubleshoot it myself. Lucky for me I have a friend/co-worker who took several HVAC classes at his community college because it interested him. He helped me troubleshoot and was ultimately the one who helped me figure it out. We did it over the phone. He lives in Florida and I live in Colorado.

I replaced the capacitor and the blower works as expected. All is well.

$8 for the part.

quote:

Originally posted by mark123:
I replaced the capacitor and the blower works as expected. All is well.

$8 for the part.

Good news ... ! I have repaired my own furnaces in the past too. Most of the time it is something simple. Though have replaced based on life span of the furnace just because.