The other day we had our gas fireplace on for over an hour. Once the logs get cranked up, we switch on the fan. The fan along with the flaming logs were burning steady for over an hour. Then out of nowhere, it just up and quits. Now the switch will not even start the fireplace, even though the pilot light is on (lit). Any suggestions or solutions?
Hopefully your issue may just be a faulty wall switch or a short in the switch wire. You can check this by jumping the TH and TH/TP terminals on the gas valve. If the unit starts, this is your issue.
Another cause may be a dirty or faulty thermopile (the largest of the 2 sticks on either side of the pilot hood. A thermopile is basically a series of thermocouples put together to create a higher voltage (which will control the main valve section of the gas valve. A proper thermopile should give you above 250 millivolts when the pilot is on(250 being close to the minimum that most gas valves will be able to operate at). First try cleaning the thermopile. Then remove the 2 leads off the gas valve and take a reading between the red and white wires of the thermopile. Anything under 250 millivolts and it must be changed. If the thermopile checks out then your issue is most likely the gas valve, and the gas valve will need to be replaced.
Since the pilot was still lit I would look at the switch that controlls the unit. Millivolt switches are usually required. Depending on the switch type just toggling it several times may get it running again. If this happens again I would be changing out the switch as I have seen this happen in the past.