Can't get my furnace to run on a generator

December 13, 2008 4:52 PM

I've tried two different generators, but still can't get my oil burning furnace to power up. Detail inside post

I'm in day two of what promises to be a week long power outage. The first generator was several years old 2KW and had a plugged carboratuer, I fixed it and got it running. It didn't run the furnace. Now I've got a brand new 6KW generator with several 20 amp circuits on it and I'm trying to run a oil furnace, which runs on a 110 15amp circuit. I have a proper generator panel hookup that several years ago did run my previous furnace fine. Both generators produced the following symptoms.

When I turn on the furnace, there's a clicking/buzzing noise for about 20 seconds, and then I get flame. It runs for a minute and shuts down. The blower never spins up to full power, it barely spins at all. The furnace then shuts down after a couple minutes due to an overheat (since the heat never gets moved by the weak powered fan blower)

I think the blower motor could have gotten taken out by a power spike when the power went down. The motor was replaced about 3 years earlier due it burning out before, and the tech replaced it with a bigger motor. I tried wiring it to a slower speed, but it didn't appear to work.

Is there anything else it could be? It should be enough power, though it also acts like it's not.

I'm not sure I should call the oil company out to service it if I'm trying to run it on a generator (they're probably swamped with calls anyways due to the massive problems here in the Northeast). No idea where I could even get a replacement motor before Monday in Central Mass either.

posted by inthe80s to Home & Garden (7 answers total)

I'd be surprised if your motor was taken out by a power surge (at least, assuming nothing else in your house is so fried that's charred and smoking). Although maybe the electronics for the furnace or thermostat were zapped?

I would look online for the service manual for your furnace and see how to troubleshoot this.

Are the wires to the motor secure? Is it possible that there's some corrosion or a loose connection causing the motor to receive less power than it needs.

Unplugged, and breaker off, so it doesn't spin up and cut your fingers off, can you turn the fan? Does it spin freely? It sounds like it might need lubrication (is it especially cold where your furnace is? That's going make it harder for the fan to spin).

Can you warm up the area where the furnace is before starting it?

And, don't try this at home, you may lose fingers, but I'd see if I could help spin up the fan using a stick (not fingers). A motor needs to push hardest at 0 RPM. Giving it a bit of a push might be enough to keep it going.
posted by zippy at 5:19 PM on December 13, 2008

Response by poster: I've got the print service manual in my files... I'll hunt it out in the morning when it's light out again.

It is spinning freely. I know the wires in the fan area are completely secure, I've even undone and reconnected them once (just wire nuts holding them.

Not sure I can warm the furnace area. It's in a basement that's probably maintaining about 45 degrees due to being below grade. It's not freezing (the floor is very wet from the seepage caused by the storm), so I'm guessing it's not the cold doing it in right now.

The thermostat is on and clicking fine, otherwise the furnace wouldn't light at all. Although maybe the internal relay or thermostat control unit got taken out. I'll see if I can test that next.
posted by inthe80s at 5:39 PM on December 13, 2008

Sure sounds like the motor is gone. Why don't you replace it. (I'm assuming of course, that you have access to a source, brand new generator and all . . .)
posted by Neiltupper at 5:53 PM on December 13, 2008

Response by poster: Generators can be found in retail stores, blower motors tend to be supply house stores (that aren't always open seven days a week, though with the state of emergency locally they may be). I agree it's not a hard thing to wire, if I had ready access to one, would be the first thing I try when it's light out tomorrow.
posted by inthe80s at 6:52 PM on December 13, 2008

Best answer: It might be an issue with the generator not putting out a clean enough AC "signal" to run the motor. If you happen to have a similar big-ass motor (attic-fan?), see if it has the same symptoms. Also, is the buzzing noise coming from the motor? Is that not a normal noise for the furnace?
posted by gjc at 8:22 PM on December 13, 2008

I think gjc has it. I know this is an issue with inverters and could be the case as well with your generator- if the signal isn't a clean sine wave, the armature in the motor doesn't get pulled the right way and the motor either doesn't turn or overheats/burns out.
posted by dunkadunc at 9:26 AM on December 14, 2008

Response by poster: I bypassed the patch panel and wired the output directly to the furnace, and that finally got the motor to spin all the way up. No idea why, there shouldn't be anything in the patch panel that would drag it down. I've got a seperate cord to the panel now, and it runs my home PC and a few other essentials fine.

thanks for all the help everyone!
posted by inthe80s at 12:54 PM on December 14, 2008