Portable Generator wont run gas furnace

Bostonbob

I am running a Champion (8000 running watts) generator to power my home during blackouts. Everything is powered in the home by the generator BUT my Rheem gas furnace.

Is this due to total harmonic distortion? Is there a portable generator on the market I can buy that will run my furnace?

mattmia2

What happens with the furnace? Nothing? Does it stop part way through the cycle?

I had a White Rodgers thermostat from the 80's that for some reason decided it was time for another call for heat immediately after the call ended when running off generator (I don't remember if it was when the blower stopped or if it was when the t-stat ended the call).

HomerJSmith

Champion generator has a THD of less than 5%. Normal AC power to the house has a THD of between 2 to 2.5%. Are you directly plugging into the furnace? You could put a line conditioner on the furnace connection. This was the solution for Munchkin boilers running on a generators. Cheaper than buying a new generator.

ratio

Check the phasing, modern furnaces are sensitive to it & won't run if the hot & neutral are swapped when running on standby power.

Bostonbob

Clarification: I am just a dumb home owner and know nothing about electricity. The gas furnace is new (2020) and the generator gets hooked up to an interlock (?) system. It doesn't cycle or do anything under generator power. When I take the house off of the generator, everything works fine. The generator is also new (2022).

I'd like to avoid a whole home generator as they are so expensive and there are some winters I don't loose power.

pecmsg

You need one that has a Clean Sign Wave.

Inverter generators are better.

ratio

Can you post a pic of the interlock system?

Normal household electricity come on two wires, with a third safety wire called the 'ground'. This is connected literally to the ground outside, and also most pieces of metal in appliances, etc. in a house. One of the two wires that power the appliance is also connected to this ground wire because of blah blah blah (technical discussion redacted). If this wire, called the 'neutral', and the other wire, called the 'hot' conductor, are swapped when they connect to the furnace, the electronics won't like it & will generally refuse to run.

TL;DR: it might be an easy fix (swap two wires), but we need more details to know for sure.

Jamie Hall

A five minute test, if Home Depot is nearby. There are small devices available for testing circuits. Like this:

Gardner Bender GFI-3501 Ground Fault Receptacle Tester & Circuit Analyzer, 110-125V AC, for GFCI / Standard / Extension Cords & More, 7 Visual LED Tests , Red - Circuit Testers - Amazon.com

Get one and plug it into a plug when the generator is running and powering the house. If it does not show the correct configuration of lights, find out why — and fix the problem.

Bostonbob

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here is a pic of the generator, cord, exterior connection, furnace, breaker panel and a control board on the furnace. When house is on generator power, the green lights on the Honeywell unit are red, not green.

mattmia2

Looking at the manual to the zone controller and finding out what the red lights mean would be the first step. It might be possible to just bypass the zone controller and manually open the zone dampers when running off of emergency power if you can't figure out what part of the zoning system is unhappy on generator power.

Since it is connected through the service panel the ground and neutral for the generator should be bonded by the jumper in the service. Since it is a 120/240v connection it is impossible to swap a hot and neutral without a lot of bad things happening.

ratio

Hmmm. All those pictures look right and if nothing burned up the first time you used it it should be wired correctly.

The LEDs on the Honeywell give status: the three on the right show the status of the zone dampers, green open or opening, red closed or closing. The ones on the left show what the furnace is (should be) doing: 'heat' and 'cool' are self-explanatory, 'fan' means that a thermostat has the fan switch turned on (it should always be on when the cool light is on, but may or may not be on for heat), and 'purge' means that the furnace is switching from heat to cool or vice versa (it just runs the fan for 10-15 minutes so that you don't blow the wrong temperature air into a zone).

Do any of the zone lights ever change to green, or any of the mode lights light up when it's running on backup power? If the zone panel doesn't do anything when you're running the generator, the problem is probably not in the furnace.

mattmia2

What kind of thermostats are on the zone panel? Are they just on/off thermostats ore are they some sort of system thermostats?

Also note that the thermostat and possibly the zone controller may lock out for 15 minutes or so after power is applied to make sure any refrigeration components are equalized before attempting to start them.

Patchogue Phil_2

BostonBob

Did you ever solve this problem?