Miller CMF80 furnace runs for 45 seconds but will not fire

Lennyz

Hey guys. I have A Miller cmf80 Natural Gas Furnace in my mobile home. The induction fan will kick on for about 45 seconds but will not fire. I tapped on the gas valve and it fired. I have now replaced the gas valve and igniter. Still having the same outcome. Will kick on for 45 seconds but will not fire. If I tap on the burner or the control it will fire intermittently. I’m not sure what to do next. I had a heating guy come in before I started changing parts and he told me parts were not available and he wanted to replace the furnace for $. That being said I took the job on myself. Any help would be greatly appreciated ...

Kickstand55

Without any details on the equipment such as make/model of burner, type of gas, pipe size, pressure and more information on how it sounded when it quit the first time, what someone did to try and restart the unit, what did the repair guy do and anything else you can add. The more, the better. Pics help a lot too.

Kickstand55

Addendum: Sometimes Miller furnaces will experience a burned out heat exchanger. Usually when not properly serviced and thoroughly checked. Excess air from the heating side of the heat exchanger can pressurize the firing chamber and cause the burner to miss-fire, or, after a while not fire up at all. But there's more...

Lennyz

Lennyz

I’m not sure what the service guy did he told me it was a possible gas valve or control board issue but said that the parts were not available and that it should be replaced. It’s A natural gas furnace. Not sure how to determine pressure. What does not make sense to me is after tapping on it it will fire and run fine until it reaches the set thermostat temp it will the Then will shut off and not fire again. No sounds from start to shut of other than the induction fan running. 

JUGHNE

I believe that inducer fan has an end switch activated by the rotation of the fan motor.
It is a mechanical centrifugal switch which closes when motor is up to speed, this allows the ignition sequence to continue.
I would guess a good cleaning might fix it.

You may have been tapping on the wrong part!

Kickstand55

Looking at the pics, the gas valve seems to have been there for a spell. The dust in and around the burner area is concerning.
I'm not picking on the guy that you said serviced the unit, but, he should have told you a lot more and offered a complete and thorough cleaning, inspection and combustion test as well as making sure clean air is getting to the burner from the duct below.
Play it safe. If you don't know anything about these things, DON'T DO ANYTHING to fix the problem yourself. Call a reputable gas service provider.
Let us know you will do this. We are here to help and want you safe.

EBEBRATT-Ed

Miller's do have a habit of loosing heat xchangers.

Try this :

Turn the thermostat down so the burner does not run. Set the thermostat to fan only. Hold a piece of tissue paper over the flame observation port with the port open. Start and stop the blower fan with your on off switch. See if the tissue paper moves when you start and stop the fan. If it does move the hx is probably bad.

Lennyz

So the photo I sent before is the picture before I did the work. This is the updated picture. Tried the tissue paper test....no movement. I’m pretty mechanically inclined and did apartment maintenance for many years so I’m aware of dangers with gas, power ECT. I however don’t have much knowledge of furnaces. I appreciate the concern. Does anyone think it could be A memory board issue?

mattmia2

you need to trace it with a meter. does the gas valve get power when it fails to fire? if not, is the centrifugal switch on the inducer and all the other safties closed? it looks like you replaced the valve? since it is a power burner you will need someone with a combustion analyzer to adjust the combustion and draft with the new valve.

Lennyz

Thanks everyone at this point it’s beyond me. As far as testing goes. I will look for a reputable repair company in the area.