Gas fireplace cycles off then back on by itself

[Citation]

I thought I might ask for some of the groups collective knowledge.

My parents have a gas fireplace that seems to light easily enough but after perhaps 10-15 min it peters out. The perhaps 5 min later it restarts on its own. I've verified the pilot light stays on the whole time. In watching it I'm wondering if the for of gas into the burner is restricted somewhere since it seems like the flame starts large then gets smaller before going out.

Other than the pilot light keeping the thermocouple hot to keep a valve open I'm not overly familiar with the details of a gas fire place.

 

[OccupantRJ]

Sounds like a normal thermostatically controlled device to me. My gas logs work like that relative to the knob setting.

 

[Citation]

Sounds like a normal thermostatically controlled device to me. My gas logs work like that relative to the knob setting.

Maybe. It seems odd that they would have to thermal cycle when the blower fan is on and the flame is set to low.

 

[cgrutt]

Thermocoupler likely needs to be cleaned or replaced. Make sure connection is tight at valve and its secured properly where it needs to be. Suppose it could also be issue with vent or gas supply but if its cycling unusually I'd look at thermocoupler first as that is controlling supply.

 

[BillK]

Has it worked differently in the past ?

 

[PoorUB]

Maybe. It seems odd that they would have to thermal cycle when the blower fan is on and the flame is set to low.

The blower is usually controlled by a cheap small disc thermostat. If the fireplace is warm, the fan is on.

 

[PoorUB]

I thought I might ask for some of the groups collective knowledge.

My parents have a gas fireplace that seems to light easily enough but after perhaps 10-15 min it peters out. The perhaps 5 min later it restarts on its own. I've verified the pilot light stays on the whole time. In watching it I'm wondering if the for of gas into the burner is restricted somewhere since it seems like the flame starts large then gets smaller before going out.

Other than the pilot light keeping the thermocouple hot to keep a valve open I'm not overly familiar with the details of a gas fire place.

Without knowing what controls are on the fireplace it is hard to say. It might be working as designed.

 

[fitter30]

Thermocouples don't cycle gas valves. If pilot goes out it a manual relite. If the there is no outside power wiring. There is a thermostat. Could be separate wall stat or one mounted log assembly below logs in the front.

 

[cgrutt]

Thermocouples don't cycle gas valves. If pilot goes out it a manual relite. If the there is no outside power wiring. There is a thermostat. Could be separate wall stat or one mounted log assembly below logs in the front.

Thermocouple (and/or thermopile) holds gas valve open when pilot light is present. No pilot light gas valve should shut. So it actually can cycle gas valve via changes in heat. If its dirty or loose heat fluctuations can open or close gas valve. Thats all I was thinking based on problems OP described. Still suggest checking.

 

[MileHighRover]

Thermocoupler. Mine was doing the same thing. Had a repair guy come out and service the fireplace. Replaced thermocouple and hasn't happened again in the last two years.

 

[The Cobbler]

friend had similar on a stat controlled gas fireplace, it was a bad connection in the millivolt stat circuit.

 

[fitter30]

Thermocouple (and/or thermopile) holds gas valve open when pilot light is present. No pilot light gas valve should shut. So it actually can cycle gas valve via changes in heat. If its dirty or loose heat fluctuations can open or close gas valve. Thats all I was thinking based on problems OP described. Still suggest checking.

They are a manual reset never a automatic relite. Have to hold a button in light the pilot hold it in for 30- 60 seconds to make 30-35 mv or in a powerpile/ themopipe 350-700 mv depend on either a round or matchbook style.

 

[HoosierBuddy]

If this is a ventless heater, It could be cycling due to the oxygen depletion sensor.

That would be a "Bad Thing" if that's what it is. The ODS tripping means that the heater had depleted the oxygen out of the room and not enough replacement O2 is making it in to properly support combustion.

I THINK that most heaters would go completely out if the ODS sensor indicates low O2...but I'm not certain they all do.

 

[fitter30]

Thermocouple (and/or thermopile) holds gas valve open when pilot light is present. No pilot light gas valve should shut. So it actually can cycle gas valve via changes in heat. If its dirty or loose heat fluctuations can open or close gas valve. Thats all I was thinking based on problems OP described. Still suggest checking.

Manually the safety has to be held down to relite then hold to fire burner. They don't cycle. It's made or not there is nothing in between.

 

[Citation]

Did anyone have a diagram showing how the gas control system for one of these fires is supposed to work?

This one has a starter button and control knob (off - pilot - 1-5) on the front of the unit. There is a light switch near by for a blower fan. The use tag on the front of the thing just talks about lighting the pilot and adjusting the flame.

This one doesn't appear to have any thermostatic control (but I didn't pull things apart to look for one). I would assume if this were a thermostatic control the fire would stay strong then just cut off, similar to when I turn the fire off with the control knob.

 

[fteufert]

Usually once lit, you do the following to adjust the "thermostat"

Push knob in and hold while turning the knob counterclockwise to LOWER the temperature it comes on

Push the knob in and hold while turning clockwise to RAISE the set temperature

That is how my ventfree Charmglow fireplace works. It is not a true thermostat but it does work fairly good

As for the switch on the blower fan, one way is to keep the fan always on, the other way turns it on and off when it gets warm enough to circulate the hot air