This is a Heatilator GC300 vented gas log fireplace with a standing pilot. We use it probably 5 hours/day in the wintertime and it's been great until this spring, when it started to shut off at random intervals. Sometimes it will shut off (pilot always stays lit) after ten minutes, sometimes may run for several hours with no problem. When it does shut off, sometimes it will re-light in about a second, sometimes it may be off for an hour or so. Sometimes it will shut off, restart, then shut off again. Turning the wall switch off and back on seems to make no difference.
Had a serviceman look at it in the spring and he said he tested everthing an could find nothing wrong, but it needed a through cleaning and adjustment, which he did. Shut it down for the summer shortly thereafter and this fall we find it doing the same thing.
The switch is just a standard 120v switch, so I took it out of the loop and just hooked the two wires together with a wire nut to see if that was the problem. It still shut down after a while, so I doubt that's the problem.
It appears to have a high limit sensor that must be in the exhaust stack somewhere according to the manual/install instructions I have. I can follow the wire from the gas valve out through the side of the unit but not sure where it goes. Can these fail intermittently? Can it be tested? Would it ever shut off after the fire has only been burning for a few minutes?
I talked to a gas fireplace shop and he says "it's the thermopile" with no doubt in his mind. The intermittent failure makes me wonder -- can they fail intermittently?
I've checked the exhaust vent outside by taking the end off and it doesn't appear to be blocked (vents through the wall immediately behind the fireplace).
I have the identical unit upstairs in the master bedroom that probably hasn't had three hours' use in the 15 years, but it's pretty tough to just make them magically trade places <G>.
Any advice on where to go from here?