My gas fireplace lights for 20 minutes then both the pilot and the flames suddenly go out?

Question

It is a ~10yr old Majestic he32tn fireplace installed by the previous owner of the house. I normally keep the pilot light out because I don't use if often, lighting the pilot requires holding down the knob for ~3 minutes before it lights successfully which takes more than average patience since the spring pressure on the knob is high.

From that point everything is ok and the unit puts out nice heat until about 20 minutes later when suddenly I hear a click/ping and both the flames and the pilot go out.

I just had a service person here today who cleaned the pilot unit, but it didn't change the behavior. I could swear once I saw it go out then come back on later, but maybe that was a freak accident, it didn't repeat tonight.

Thanks in advance for your advice!

Could this behavior of switching off (then back on?) be on purpose to regulate temperature? (How would the pilot be re-lit?)

Answer 1

Sounds like a 'duff' thermocouple, similar problems occur with gas boilers. But your fire will not switch its self back on once it has gone out.
The thermocouple is not expensive but the fitting of it may be, shop around qualified service men.

Answer 2

Budding Author's answer is good.