Flame Stops and Starts

[HRTKD]

I have a Heatilator gas fireplace with the static pilot light. The pilot starts well and runs well also. I cleaned the thermopile and the thermocouple. Voltage reading on the thermopile looks good. 500 mv with just the pilot light and 300 mv with the full flame.

The flame will come on for about 15 minutes from a cold fireplace and then shut off for a few seconds, then start up. It then does this over and over. Sometimes the flame will stop and not restart on its own. When this happens, if I flip the switch, it starts right up. While this is going on, the voltage reading from the thermopile doesn't deviate.

I'm stumped. I'm not sure if this is an electrical issue or a gas flow/regulator issue. I can't find a match of my symptoms on the Internet or YouTube.

 

[DAKSY]

What model Heatilator?
What switch do you use to operate the unit?

 

[HRTKD]

Model is GNDC33 NAT. It's also the the high altitude model according to the label. Install date was around 1988.

I haven't opened the switch. I had assumed it was a standard wall switch. Is that not the case?

 

[DAKSY]

Thanks. Some of those older models have a tech switch under the firebox. If your switch is all-mounted, it should be a standard switch. Pull the switch & jump the wires. Does the unit keep burning? If so, the switch is probably faulty. Replace it & you should be good to go. If it's STILL acting up, let us know.

 

[HRTKD]

Thanks. Some of those older models have a tech switch under the firebox. If your switch is all-mounted, it should be a standard switch. Pull the switch & jump the wires. Does the unit keep burning? If so, the switch is probably faulty. Replace it & you should be good to go. If it's STILL acting up, let us know.

Will do. SWMBO likes the fireplace for some reason. I'll have to post a picture of the tilework I did around it.