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My home was built in 1957, I had a new heat pump system put in (which I now hate) 7 years ago. It works fine in the summer, but in winter it doesn't heat the house very well.

At the time, I kept the old Coleman, through the wall natural gas heater as emergency heat, as works without power to the house. It's old and inefficient, but it's done it's job for 50+ years. This year I replaced the old thermostat,with a new Honeywell round heat only mode. I haven't been able to get it fired up once this winter though. I've contacted a couple of local heat/air places, and noone has ever heard of this heater and don't know how to service it apparently.

So I'm trying to troubleshoot it myself and see if the problem is the thermostat, or the unit itself. Am I correct in thinking that if I manually touch the two wires together (red/white), sans thermostat, the unit should come on if it's going to?

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  • What is the model number of the furnace (likely printed inside the unit somewhere)?
    – Tester101
    Commented Jan 19, 2016 at 19:20
  • @EdBeal wants to know if the pilot is lit?
    – Tester101
    Commented Jan 19, 2016 at 22:03
  • I have no idea what the model number is, I've been unable to locate any numbers anywhere. Just an attached metal tag that tells you to clean the gas valve and burner area frequently. Yes, the pilot is lit, and burns fine.
    – Bhamrichard
    Commented Jan 21, 2016 at 3:46

4 Answers 4

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I assume you are dealing with a gravity wall furnace, now made by Williams and Empire, and commonly found in California. They require no AC power. They use a thermocouple on the pilot light to power (via the thermostat) a millivolt gas solenoid. They sell special thermostats for this application. A "common" thermostat may or may not work, depending on its ability to switch a very low voltage at comparatively high current, and function without 24v power.

Electronic thermostats cannot work, unless you supply 24v to them and supply a relay to switch the millivolt line... but that makes the furnace dependent on AC power, which defeats the purpose of this type of furnace!

Yes, touch red and white together, and the unit should come on.

If it does not, first check that the pilot is on (no pilot, no millivolts). Then check the 2 wires with a voltmeter, there should be some fraction of a volt of electricity. If not, the pilot is out or you have a thermocouple problem.

Parts are readily available for Empire and Williams furnaces, and worse comes to worst, you can replace one in-kind, though you'll have to special order it in the northeast or midwest. For some reason, people in those areas have a revulsion to furnaces that work without electricity.

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  • Yes this is a milivolt system and there is a thermopile directly in the pilot light. The pilot I have no problems with it fires up fine and burns clean looking I've jumped the two thermostat wires and the furnace doesn't fire up so I'm assuming a thermopile problem or gas valve. After all it IS 50 years old! There are two of these units still in the house, one we used constantly when I was a child, and the other hardly ever got lit up unless temps hit the teens. I'm tempted to pull the thermopile from the other unit and see if that's the issue. If not I'll have to assume the gas valve.
    – Bhamrichard
    Commented Jan 21, 2016 at 3:44
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Your line of thinking is correct, in that a thermostat is simply a switch that connects two (or more) conductors together. If the thermostat is wired following common patterns, then connecting the red and white wires together should tell the furnace to try and fire up.

If the unit works with the power off, then the control circuitry is likely powered by a thermopile. If this is the case, then the pilot must be lit to power the control circuit.

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  • Is the pilot lit?
    – Ed Beal
    Commented Jan 19, 2016 at 20:23
  • @EdBeal How should I know?
    – Tester101
    Commented Jan 19, 2016 at 20:59
  • I meant it as a comment for Bhamrichard
    – Ed Beal
    Commented Jan 19, 2016 at 21:47
  • It doesn't. It works with the power out, so obviously, it doesn't use a 24VAC transformer.
    – Harper - Reinstate Monica
    Commented Jan 20, 2016 at 2:20
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    I'm going to end up having to find a new thermostat for this thing one way or another, the old one I had has just plain worn out. The one I bought at the local hardware store seems to be a 24v, and will not work with this heater. In either case, the heat doesn't come on absent a thermostat so I'll be checking voltage at the gas valve to see if the thermopile is functioning. All of the wiring is original, and still very tight. Might be a simple replacement part issue.
    – Bhamrichard
    Commented Jan 21, 2016 at 3:50
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This looks like an old post but I’ll answer it anyway since it may help someone else. Newer wall heaters have what is called 100% safety meaning if the pilot generator is bad or the pilot is not lit the gas to the pilot will shut off. Older furnaces have what is referred to as a 90% safety meaning if the pilot blows out or the pilot generator goes bad gas will still flow through the pilot but not the gas valve. You can check the pilot generator with a volt meter. It should read at least 125 milivolts. A 24 volt thermostat will work with a milivolt furnace. 24 volt thermostats have what is called a heat anticipator, a small coil of wire with a metal tab over it. Slide the tab all the way one way and try it if that doesn’t work go the other way. It is easy if you have an ohm meter, connect one lead to r and the other to W. Move the little metal tab until you get as close to 0 ohms as you can. If you are getting less than 125 milivolts at the pilot generator then replace the pilot generator. If you are getting more than 125 volts at the thermostat wires and when you touch the wires together it still doesn’t come on it is either the gas valve or the thermostat wires. At the gas valve jump the two terminals where the thermostat wires come in. Still nothing it is the gas valve. One note of caution, wall heaters can be very dangerous from a carbon monoxide standpoint. Before using a wall furnace that has been sitting for a long time it would be best to have the gas company or someone that knows what they are doing to check the safety aspect of the wall furnace.

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I had a simular problem with mine. It was the solenoid valve in the regulator. It was a Robert Shaw Regulator and they are pretty easy to find at a resonable price.

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