Greetings; I have a York Stellar furnace that I am guessing to be about 20 years old. Lately it has been doing the following.

1. Thermostat requests heat.
2. Blower starts up.
2. Pilot light comes on,(Glows Yellow).
3. After twenty seconds there is a click and then one of the following happens;
40% of the time no blue flame, pilot light shuts off, blower runs.
40% of the time burners light up but shut off after 20-30 seconds, blower runs.
20% of the time burners light up and stay lit until reaching temperature set on the thermostat.

After doing some research, I removed and sanded the flame sensor. Still the same issues as above. I have blown into the blower diaphragm tube and there is not really any resistance so I'm assuming it is unobstructed. I have cleaned all filters and vacuumed what I could safely reach in the furnace control area.

As I said the problem is intermittent. If I throw the power switch for the furnace enough when the thermostat is requesting heat, eventually it will stay lit up. I usually then set the thermostat for some really warm temperature to carry the house through the night.

Any thoughts would be appreciated. I'm starting to suspect the control board is faulty.

Cheers

https://www.askmehelpdesk.com/heatin...ms-423853.html

See post #4; checking flame sensor

Thanks; I ran that test and it read 0 uA. Yet the furnace still occasionally runs. I would have assumed that if the flame sensor was shot that it would not allow any flame after a few seconds. I am finding now that even when I do get it to run for a longer time it always shuts down before reaching the temperature requested on the thermostat. So without ruling out the flame sensor as still being defective, what would be the next most likely culprit?

Cheers

Make sure the fuse isn't blown. Remember you have to use different jacks for current.

Grab a 9V battery and a 1.5 Megohm resistor in series to test your meter. That should read ~6 uA. R = 9/6e-6.

Get a few 1 meg resistors from Radio Shack. Put two in parallel and 1 in series with the parallel combination to test your meter.

There is electronics on the board and they could be defective.

It's best to check your meter reads correctly first.

Check the wires that connect the flame sensor. Loose or high impedance is a signal killer.

Sometimes cleaning the flame sensor does not work so the flame sensor could be defective also.

The next step could be expensive so the flame sensor is always first especially on a 20 year old furnace. While you are at it also check the grounds.

Thank you all for the advice but it was for naught. I had a technician come today and I explained what had been happening. I went upstairs and two minutes later he came up and said that three of the four heat exchanger ports (I think that's what he called them) were cracked and he had to red flag the furnace. I guess I need a new one. Merry Christmas indeed.

Thanks Again
Cheers

Sorry to hear than. I did mention that the next step could be expensive. Get 3 estimates and follow the link below for a good job.