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#61928 - 02/05/06 04:22 AM furnace or generator problem?
rdderrick Offline
Junior Member

Registered: 02/04/06
Posts: 1
I'm trying to use a backup generator to power a limited number of circuits in a house. I am using a Reliance Power Transfer Switch box to take power from the generator (rated 5000W steady state and 6250 starting) into selected breakers in the switch box. All the other circuits work, but the Trane XE 80 furnace/blower will not start/run.

I've run a number of scenarios trying to figure this out. With power into the panel I open all the breakers except the one for the furnace (15amps). The furnace works. Again, only power in house is on that breaker.

However, when I run the generator and switch to generator power on the same breaker, the furnace will not start. I've checked the voltage (with the generator running the circuit) at the furnace and it reads ~ 130V AC. It's getting power to the circuit but for some reason the furnace will not kick over.

I even changed around the wiring on the Reliance relay box in case there were problems with that (which is probably not case since I have 130V at furnace anyway). I've even tried just powering the one breaker with the generator.


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#61929 - 02/05/06 06:36 AM Re: furnace or generator problem?
Tom Offline

Registered: 01/01/01
Posts: 1069
Loc: Shinnston, WV USA
You might want to take this up with the furnace manufacturer. With all the electronics that they're using nowadays, it is possible the furnace doesn't much care for a diet of generator power. Could be you're not generating 60hz or something else is out of the tolerance range for the furnace.

Few things are harder to put up with than the annoyance of a good example.

#61930 - 02/05/06 07:37 AM Re: furnace or generator problem?
LoneGunman Offline

Registered: 10/02/05
Posts: 141
Loc: Florida
Is the transformer for the Tstat being powered when you switch to genny power?

#61931 - 02/05/06 07:52 AM Re: furnace or generator problem?
deverson Offline

Registered: 03/07/05
Posts: 20
Loc: Mosinee, WI USA
Is there a time delay built into the furnace so it doesn't start for a few minutes after power is applied? I've been caught by AC equipment on that one.

#61932 - 02/05/06 08:02 AM Re: furnace or generator problem?
Rewired Offline

Registered: 01/01/06
Posts: 567
Loc: Hamilton, Ontario, Canada
I have a similar setup with a backup gennie at my place and only once I have had the furnace act weird, and that was when the gennie was loaded down and the voltage dropped to around 100 or so volts... The furnace control board kept picking up and dropping out the fan motor but that was about it.... I did have to tweak the govenor on the gennie to make it produce the proper output at the proper frequency under mid to heavy load and since then I have had no problems whatsoever...

Believe it or not, with a 4500W gennie I can run 2 referigerators, a freezer, and THEN start up my furnace and Central A/C and have no problems..


#61933 - 02/05/06 09:35 AM Re: furnace or generator problem?
Electric Eagle Offline

Registered: 04/20/02
Posts: 928
Loc: Alpharetta, GA
The problem most likely is power quality. The circuitry in the furnace is sampling the incoming power and it thinks the power is coming on and off. We have the same problem with computer UPS systems, but a high quality UPS has button to adjust the sensitivity, however a furnace doesn't. I don't really have a good solution for you other than maybe a conditioner. A portable generator will never produce really good power. A cheap permant generator will only be slightly better, but good enough for the furnace. They do make power conditioners, you might try one.

#61934 - 02/05/06 09:47 AM Re: furnace or generator problem?
mxslick Offline

Registered: 10/24/04
Posts: 785
Loc: Atomic City, ID USA
I've checked the voltage (with the generator running the circuit) at the furnace and it reads ~ 130V AC.

That's most likely the problem. If the voltage coming out of the generator is out of spec then the frequency is also likely to be off too.

Adjust your generator to produce no more than 125volts no-load and try it again.

Hope that helps!
Stupid should be painful.

#61935 - 02/05/06 11:24 AM Re: furnace or generator problem?
Sixer Offline

Registered: 08/08/05
Posts: 264
Loc: Canada
One obvious thing to check is polarity. We were doing a panel changeover in a house this winter, and it was quite cold outside. I had my generator running outside to supply us with some lighting and power for drills etc, and we also ran a temporary cord to the furnace so it would run too. The apprentice had the polarity wrong, so the computer in the furnace would not allow it to fire. (always blame it on the apprentice )

"Will it be cheaper if I drill the holes for you?"

#61936 - 02/05/06 11:38 AM Re: furnace or generator problem?
Larry Fine Offline

Registered: 02/18/05
Posts: 684
Loc: Richmond, VA
Another possibility: the HVAC system's 24-volt transformer may be in the outside unit, not the usual inside unit, and not receiving power during generator use.
Larry Fine
Fine Electric Co.


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