cmf 80 code 3

[rapinatore]

model: cmf 80-pg conv
serial: cmf9909-01450

just moved in and it's cold. furnace ran for a few days fine but then started going to lockout with code 3: Three flashes - the control is in lockout
because a failed ignition attempt, a gas
valve error, or a false flame sensed
during the warm up period. A false
flame condition exists when the flame
sensor senses a flame without a flame
present. If a false flame has been
sensed, the control will only return to
normal operation after the false flame
condition is no longer present.

so first i cleaned the airbox fan and motor (was caked w a 1/4 of dust/grime). Then we got a code 2 which is centrifigal switch. So i removed the intake motor. It was barely turning but not really. Some oil and a little banging around and it was running strong so i reinstalled it. Code 2 went away but code 3 came back on. So i removed the igniter assembly. The ignitor looked fine but the difuser plate has a 2 inch crack running from one side to the center. The plate is solid so i did not replace it. An hvac guy happened to be at the store when i went to get a new ignitor and he check the resistance on the ignitor and said it was much to high, so i bought a new one there. The one they sold me is nordyne part no. 902661 it's made by partners choice sku 902661a. The ignitor location is obviously a problem as the bracket is very pliable. the box says 3/16 from the burner, but i've tried many positions but still a code 3. Certain ignitor positions wouldn't allow it to light, others caused a loud ignition of the gas, but right now it's as close to original as i can tell. I found a different gas orrifice laying inside my furnace so i swapped them from a 50 which is what was in it to the 20 i found and still a code 3. Also i've noticed the ignitor runs longer if i adjust the air intake to the most constricting position limiting the air flow as much as possible.

Still the furnace turns on the intake motor. Lights the ignitor burns for 1 to 5 seconds (depending on which combination of the above tuning i do) then it cuts out. The ignitor turns off and repeats twice more. After the ignitor cuts out the third time the control module goes to lockout with 3 flashes.

I have not yet called a service tech to come over as I am typically successful with diy projects, my dads an electrician and my father in law has some experience working on similar furnaces. This is becoming increasingly frustrating especially since i can't find my electric space heater , lol.

[furnaceman]

I'm not completely familiar with this unit, however,u said it ignites for a few seconds, do u mean the ignitor just glows or do u have flame? If u have flame, it sounds like the flame sensor is not detecting the flame. If this is the case u can use a piece of LIGHT sand paper or a green kitchen scratch pad and clean off the sensor, this usually works, if not u either have a bad flame sensor
or possibly a bad board.
U would have to use a meter to mmeasure the micro amps of the flame sensor to see if it is bad or the board is bad

hope this helps

[Robert]

Hi,

The 902661 ignitor is also the flame sensor, so cleaning is not an option. If it were, use steel wool, not sand paper to clean the sensors.

With all the adjustments and tuning you have done, it is not safe to try any DIY from here without being there in person.


Time to call in an hvac tech who can get it back to original specs, then properly troubleshoot and diagnose the problem.


I am locking this one down from any further replies due to safety concerns.



Thanks,
Robert