Furnace won’t run on generator?

[AldeanFan]

Asking for a friend.
My friend’s power was out for 52 hours last weekend. He has a champion inverter generator that is about 3500 watt, I don’t know the exact model.
He attempted to run his natural gas furnace off of the generator but it wouldn’t work.

He cut the male end off of an extension cord and connected the wires to his furnace inside the access panel (after disconnecting the furnace from house power).

The exhaust fan would run but the furnace wouldn’t fire.

Luckily his gas fireplace kept the house warm.

We can’t determine why the furnace wouldn’t run on generator power.

My similar furnace plugs in to a receptacle next to the furnace so I can unplug it and plug in to an extension cord from my generator. My generator is a Honda eu2000 and I have successfully run the furnace on generator power.

Any reason the furnace wouldn’t run on generator power?

 

[dogdog]

did you check if 24vac is proper on the transformer end input and output. Lots of generator type is pretty harsh on transformers.

 

[PCustoms]

Seems like a similar issue was posted last year, maybe you can dig that thread up for an answer.

 

[kaymccampbell]

The two things I have seen are, the neutral not bonded to the ground, and running the generator in ECO mode. And then there are just some furnaces that won't run on inverter power.

 

[Jeepster04]

Some people said the floating neutral will mess with the furnace. I bought a bonding plug but haven't tried it again.

A regular generator worked fine with my furnace.

 

[Noltz]

Furnaces flash codes when they won't fire. I'd be looking there first. I'm assuming it worked once power was restored?

 

[Dagny]

didn't get it from me but yeah ground the neutral.

 

[Hot shot]

If it has an igniter instead of a pilot light the igniter might not be getting hot enough to open the gas valve. Might not have enough voltage to the igniter or igniter could be bad
I’ve replaced the igniter on my gas oven
Here’s what the one on my oven looks like

 

[nadogail]

I would be having a conversation with both the furnace manufacturer and the generator manufacturer.

 

[Terry D]

I had the same thing happen when using a HF 2000 watt inverter generator. Turns out the generators neutral was not bonded.

 

[PCustoms]

Seems like a similar issue was posted last year, maybe you can dig that thread up for an answer.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.garagejournal.com/forum/threads/furnace-ignitor-not-working-on-generator.475760/&ved=2ahUKEwiTpObw-6f8AhXDGlkFHRIeDekQrAIoAHoECCAQAQ&usg=AOvVaw3VplmlbgcGoyDbtiafGz4H

 

[AldeanFan]

Thanks for the replies.
Yes the furnace worked fine after the power came back on.

Bonded neutral is beyond my comprehension, but we have a friend who is an electrician so I’ll discuss this with him.

 

[mike93lx]

Good reminder to test these backup systems before you need them

 

[bonneyman]

I hate playing "phone doctor" but modern furnaces are very picky about grounds and polarity. But I have no experience with inverted power, so.....

 

[Jeepster04]

Thanks for the replies.
Yes the furnace worked fine after the power came back on.

Bonded neutral is beyond my comprehension, but we have a friend who is an electrician so I’ll discuss this with him.

You can buy a plug from the interwebs that does it for you. Looks like an extension cord plug without an extension cord on it.

Now that Ive said that, I bought the plug, but haven't tried it again to see if it works. So I could be wasting your time.

https://www.amazon.com/dp/B07F4R7BDL/?tag=atomicindus08-20

 

[larry4406]

You can buy a plug from the interwebs that does it for you. Looks like an extension cord plug without an extension cord on it.

Now that Ive said that, I bought the plug, but haven't tried it again to see if it works. So I could be wasting your time.

https://www.amazon.com/dp/B07F4R7BDL/?tag=atomicindus08-20

Or simply buy a replacement plug and jumper the neutral to ground with a short piece of ground wire from a piece of 12/2 Romex.

 

[Dan H]

Or simply buy a replacement plug and jumper the neutral to ground with a short piece of ground wire from a piece of 12/2 Romex.

I've already wired in a male inlet plug on my furnace, just in case but hasn't been used. As I'm thinking through this I can NOT jump the neutral and ground on my inlet plug because then my regular power will have a ground loop.

I will either have to rewire this inlet plug and isolate it from my regular power OR have a bonded neutral/ground extension cord just for the furnace?

 

[nadogail]

Sound like a "Power Quality" issue. What does the AC Waveform look like on an oscilloscope?

 

[Innovate1]

Sound like a "Power Quality" issue. What does the AC Waveform look like on an oscilloscope?

Although I have an oscope at home and use one regularly for work a lot of people don't have easy access to one. Might be the issue but I would be checking things like bonded neutral first.

 

[brewchief]

Need to check voltage and hz, every single furnace I've installed in the last 20 years has has a section regarding generator power and the tolerance that must be maintained.

Typical would be 120 volt plus/minus 10% (108 to 132 volts), 60 hz plus/minus 5%(57 to 63 hz) and wave form distortion of less then 5% THD.

I've personally seen a furnace that wouldn't operate because with voltage in spec but at 63.5 hz. We ended up plugging in an electric heater and it loaded it just enough to bring the hz down to 62.5 and it would operate at that point.

 

[Denwood]

Let me guess..he has a newer furnace with ECM motor and digital controls, correct?

The inverter gen would work fine, however it's almost certainly an issue with the neutral not being connected to ground (bonded). You can do this yourself with an 120V plug and jumper between ground and neutral. If he installs a generator subpanel, it would do the same. You need to the do the same if trying to charge an EV using an inverter/gen.