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Need help diagnosing my non-working gas wall heater.? Answered

Hello, I live in Arizona so we just tried to use our gas wall heater for the first time tonight (hasn't been necessary before now).  This is the type of heater we have installed in our hallway/bedroom. http://www.homedepot.com/buy/williams-monterey-50-000-btu-natural-gas-top-vent-wall-furnace-5009622.html#.UJ-qvYaElhE

I lit the pilot and then moved up to the thermostat that is mounted on the wall.  I moved the dial from the left (which starts at 50) over to the far right (which stops at 90).  I felt and heard the thermostat click over at about the 65 degree mark (which seems accurate to me), but nothing happens.  Usually, immediately after the thermostat clicks over, the gas flow increases, and the heater starts to do its thing.

I have included some pictures of the thermostat, and heater itself.  If someone could tell me which connections I need to check with a volt meter, it would be greatly appreciated. One thing I want to add, we had a light socket go out on the same wall about a month ago, that doesn't seem to be getting any power.  I have tried several new bulbs and it doesn't work.  So I would need to figure out how to check if the thermostat is even getting power as well.  It's possible that the thermostat isn't even getting power. Thanks

SOLVED:  Thanks everyone for your replies.  It actually was the solenoid inside of the heater, but the good news is it works fine, a wire just came loose.  Everything is working great now.  I wouldn't have thought to look there if it wasn't for your comments.  Thanks again!



Best Answer 5 years ago

@rickharris: I've never seen 'mains' coming into a thermostat -- its only ever 24vac from a transformer in the furnace in my (north american) experience. Closing the circuit will either call for fan, heat, or cool depending on which wire is connected.

That said, if there is a physical click in the thermostat, sounds like it is functioning at least mechanically.

On the furnace side, it could be a bad main gas valve/solenoid, which would still allow the pilot light to function but not enable the main valve. A bad thermocouple could convince the main valve not to open thinking the pilot is flamed out, it is usually the quickest/easiest fix for a furnace that won't light -- but a bad thermocouple generally means the pilot light won't stay lit. If you aren't sure about the valve, get a QUALIFIED TECHNICIAN to look at it - messing with gas lines is a good way to blow up your house. There are never user serviceable parts in a furnace valve.

Edit: to test, set your multimeter to Volts AC - and test the red/white wires coming into the thermostat and screwed down on the bottom terminals. There should be a voltage on there of 24-48VAC

if you get a length of insulated (so you don't shock yourself) wire with stripped ends and short the 2 terminals, (red and white in your picture) where the wire comes in the wall, the furnace should turn on, or at least being its power-on cycle.
If you take the cover off the furnace, what do you see?

Hi @Frollard, I have the same model of wall furnace and have a similar problem, I'm hoping you can help me. The pilot light stays on, but the furnace will not come on. I replaced the thermostat from digital to manual but that did not solve the problem. The connections at the thermostat read 30 VAC and all wires are secure. There is voltage on all the wires below as well. When I put the two leads of the multimeter on the 2 terminals at the thermostat the furnace came on. Does this mean the gas valve/solenoid needs to be replaced? If so, is that something an ambitious DIYer can do or should I call an expert? Thanks in advance for your help.


Thank you everyone for the replies! Frollard, you were right. It was the solenoid actually inside of the furnace.

The good news; it wasn't bad, simply had a wire come loose! Everything is working as intended now, and thanks again for your replies, because I wouldn't have even thought to look back inside the furnace panel.

We get them directly connected here in the UK in older properties - Mine is a low voltage version as well.

Addendum: There is often (but not always) a switch, like a light switch between mains and the furnace itself, often 'near' the furnace. Make sure that is turned on. It might even be in the wall cavity with the furnace. Make sure the breaker for the furnace/wall with the light is turned on.

Knocked any nails into the walls?

IS there a reason you know of why these 2 events might be linked - Building work, flooding, or the like.

Your thermostat acts as a switch - Live mains in - switched by the contacts and live mains out - there may be a neutral that is linked across in the thermostat - Take care Mains electricity bites.

That seems extremely dangerous since they often have exposed terminals to connect the wires. yikes!

My next door neighbour has such a thermostat where it acts as a switch for the hot water pump. It has a plastic cove on it of course so nothing is exposed.

He is about to have a new CH system fitted so I guess the new boiler and thermostat will be low voltage. Guess Ill end up having to show them 100 times how to set the controller. We had enough trounle when their family bought them an Ipad.

Frollard knows whats up.

You need to open the system up. It could be the solenoid that controls the gas valve isn't working or is stuck. Regardless of what the problem is it would be best to get a certified technician to deal with the problem.