Heat n glo sl550trs-c diagnosis help

superds

Hello,
Current situation is my pilot light gas fireplace insert turns on when I flip the manual switch on the valve.

When I turn off the manual switch It stays on when my thermostat is in “heat on” mode or when the thermostat is disassembled and the wires are crossed.

It turns off when the thermostat is switched to heat off mode or when I uncross the wires.

Neither switching thermostat/temp to “heat on” (and thermostat clicks) or crossing the wires will turn on the fireplace, only flipping the manual switch will turn it on.

Any ideas on diagnosing issue ?

EBEBRATT-Ed

You can go on Heat N Glo website with the correct model # and find the service manual. That would be the place to start. The model # you posted does not seem to come up.

If the fireplace has no electrical power to it other than the thermostat wires you probably have a "millivolt system" where the pilot flame generates enough electrical power to allow the thermostat to operate.

You could have a bad power pile which is the flame sensor that generates the power.

Bob Harper

This fireplace uses an either/ or switching system but not both simultaneously. The unit comes with a manual on/off integral low voltage rocker switch if it is a millivolt standing pilot system. You have the option of extending this switch leg to a low voltage single pole wall switch or a thermostat. If the stat falls off and the rocker is still closed then the valve will remain open.
An Intermittent Pilot Ignition or IPI system works the same way- either/ or but not both.
You can Ohm-out the switch leg(stat). If the thermocouple on a millivolt system is weak, the pilot can dropout. If the thermopile is weak, the valve may have trouble opening. Recommend professional service.

superds

Yes it’s a Milivolt system with pilot light. sorry for not explaining more. I changed the thermocouple last year and I figured since the valve stays open when the manual switch is open it isn’t the thermocouple. If it wasn’t producing enough electricity the valve wouldn’t stay open would it ?

By random chance later this afternoon, I was getting tools out of my closet and noticed the thermostat wire was out of the guide clips. I fixed it and heard a whoosh of the fireplace turning on. So I think I may have a damaged thermostat wire in the crawlspace.