Miller CMF-80 PG No blower?

[slimm]

Hello all first post here.

Although I'm a pretty competent DIYer I have almost no clue when it come to heaters so please bear with me and I will describe as best I can.

Yesterday morning I woke up cold obviously with no heat. I checked the Tstat and it was at usual temp. I turned it down, then back up heard the "click" inside then waited for a minute or two and hear the furnace start to make noise. It usually hums for a few minutes and then the blower comes on. After hearing the familiar hum, I went back to sleep.

A few hours later I wake and I'm still cold. I observe furnace humming, but no blower. I go outside, and it seems as I let myself run out of LP. No biggie, got out electric heater and ordered propane which came about an hour ago.

After everything delivered (and turned on) I tried to unsuccessfully turn my heat on. Same drill as before, turn up Tstat, hear click, wait for hum, and no blower after about a minute (usual time I hear blower motor kick on)

I opened up furnace door looked around for something I could possibly break and saw a silver Honeywell box wired up. Pushed the button and the blower came on, so at this point I'm guessing all is well with that.

I'm pretty stuck (and chilly) at the moment. I have located a copy of the manual online and tried to look for anything, but it's all a different language to me. I'd appreciate some suggestions, and hoping we can get it running.

Thanks in advance

[Robert]

Hi,

So the burner is igniting and everything fine except just no blower to circulate the air ???


If so, possibly a bad fan switch and that is the fan & limit switch combo box you pressed the manual fan switch for.


Thanks,
Robert

[slimm]

Hi Robert,

I'm assuming the "hum" is the burner igniting? Like I said I'm a bit of a newb when it comes to heating.

My mother in law (who gave us the home) says this never happened before but she does not think the pilot is lighting. I'm attaching pictures so maybe I can grasp thing with what I'm reading.

First is I don't know what gas control maybe? The black button in the bottom right corner would be to light the pilot?

Second is the fan switch correct?

If all else fails and I need a new switch would I be able to manually turn it on to get heat?

EDIT I'm also assuming even though I was able to turn on the fan with the switch it could be faulty and not work correctly in other ways?

[slimm]

In more research, I also read where someone had a problem with the same model not working and reset a limit switch? The manual I'm looking at states if I'm looking at the right thing that it is a red button, however mine does not appear to have one.

Will I be able to view a pilot light on this unit? when I open up the cover, I do not see a pilot, but I don't recall ever seeing one. everyone just tole me it is hard to see. Would I be correct in assuming the burner would not ignite if there was no pilot?

[slimm]

UPDATE:

I just replaced fan & limit switch, and I'm still getting the same result. I think I'm getting confused between my model and possibly an updated CMF80. Mine seems to be original from 1983 the manual I'm looking at online is much later, so things like blinking LED's and reset switches don't appear to be on my model.

Would I be able to see the pilot light? Would I see a spark when I push the ignitor?

The hum it seems is coming from a motor located in the vicinity of the gas control. Would the motor even run without the pilot on?

[Robert]

Hi,

See if you see a DI after the CMF80-PG in the model number like CMF80-PG-DI ???


Yes, you would see a pilot. There won't be an ignitor IF you have a pilot.


Not sure what motor you refer to as humming, can you take a pic of it ?


Thanks,
Robert

[slimm]

Hi Robert,


All seems to be working for the most part now. After poking around I did see the pilot, although it tends to go out when it feels like.

Problem now is the pilot seems to not burn "even" I guess you would call it. So my un-tradesman guess would be that with the pilot burning erratically like it does, and combined with what I'm assuming is an old (furnace hasn't been serviced in 5 years) thermocouple is causing the problem I have now.

Anywhere you can point me would be appreciated. Also when I was searching yesterday, I seem to remember you advising someone of the usual fan limits for this model, however I guess I didn't bookmark it and cannot seem to locate it in a search. Could you please advise me of the general limits so I can see if everything is up to par?

Thank you.

[Robert]

Hi,

The fan & limit assembly is showing as no longer available with no info on the limits.

The average fan temps are around 120/130 cut in, 90/100 cut out and 180/200 limit temp.


Thanks,
Robert

[Rod]

Cut out 95
Cut in 115 ( you could adjust this to 120 but no more)
Limit 190

To adjust settings turn off power. Remove cover from control box push the silver disc in to hold in place and adjust tabs to proper settings.


FYI the CMF's from the mid 80's to early 90's are notorious for the heat exchanger cracking directly behind the fan/limit control box. To check for this turn off breaker to furnace, remove cover from fan/limit control, remove the 3 mounting screws, remove the sleeve/heat shield. (this just slides out) Then shine a flashlight through the opening downward at a slight angle. You will see the front of the heat exchanger and you are looking for a vertical crack in the metal.

I'm not saying you will have this problem for sure its just a common from the era your furnace appears to be. Its a good idea to check this for safety. We check this on every one that we service in the field.

Let us know how you make out.

Good Luck
Rod

[slimm]

Thanks for all the help.

It seems as I had it set pretty close to what was mentioned.

I'm going to have it serviced in the spring so hopefully any other possible issues will be worked out then.

[Robert]

You're very welcome, happy to help.


Take care and best wishes,
Robert