[yuri]

I have a York furnace that is igniting, but not holding its flame. I know the usual suspect is the flame sensor, so I've cleaned it, and even replaced it. As I continued having the same issue, I tested the voltage of the flame sensor line to ground, and it only shows 3.75 volts. (I did want to test the micro-amp reading, however, my multi-meter only supports milli-amp.).

I believe the voltage should read much higher, like 90-120v? Does anyone know what would cause this? Hoping I can fix this and not have to replace the entire controller.

As a tech we never have to or check that voltage. You need to check the DC micro amps. The flame sensor needs to be perfectly clean and if you got oil or anything on it from your fingers then clean it with clean steel wool or #800 emory paper. You also need to clean the face of the burner it sits in front of down to bare metal or the metal in front of the sensor which ever is closest.

It works with DC flame rectification and current passes thru the flame and converts to DC volts / current and then finds it way back to the board thru grounding. Make sure the board is properly grounded also. You can check from C on the terminal board to bare metal and should have 0 or low ohms. Make sure the flame sensor wire is not burnt/bare or damaged and shorting to ground.

 

[yuri]

If the flame is hitting it correctly it should produce a minimum amount of current and that is where a micro amp reading is necessary. Usually when it is below .5 ma then it runs for 15 seconds and lockouts on low flame signal error code. If you are getting no ma then I think the board is shot or your flame sensor wire is shorting to ground. Never had that happen but I have seen some black and burnt and bad looking wires. If the flame sensor wire goes into a molex connector pull it and make sure all the pins are forward and seating properly. You may be able to buy a basic Klein meter at HDepot for under $100 that does micro amps.

Post a pic of the sensor and burner firing or video here.

 

[yuri]

Try clean the face of the burner in front of the sensor BUT it needs to be clean down to bare metal so I would remove it, OR if the distance to it is greater than that of the furnace wall metal in front of it clean that metal. My Sister had a York and that distance was real close and when I cleaned it I got a better reading. I would clean both. Rust and corrosion work like insulation and even though it may not look bad it is. .5 ma is usually minimum and .1 definitely is too low. Some of those units are pretty finicky.