Monessen HVFL18NV Pilot
I was asked to install a customer-purchased part, a pilot assembly, with thermocouple and powerpile. She had fought lighting the pilot for a month, then bought the part mail order.
The new parts do the same thing, pilot goes out when I release the button. The thermocouple is getting hot, and producing some milli-volts before I loose my grip on the button and thermocouple and meter leads. I think powerpile is not needed, since there is no remote thermostat on this.
My experience with other thermocouples tells me that we likely need a gas control, but I don't know if there is a fireplace specific issue I don't know about.
PM me if you don't want to discus this in the open forum.
This is a ventfree gas appliance that requires an OEM Oxygen Depletion Sensor or ODS pilot. Yes, it does need both a TC and TP and since you don't understand why that is good enough reason not to be working on this set. Refer the matter to a qualified hearth service technician who is NFI Gas certified. Otherwise, you could blow yourself and the house up, cause sooting or carbon monoxide or other problems. This is not your typical furnace control and definitely NOT a DIY issue. Just because you may be a HVAC pro service tech does not make this DIY. No offense but this is not the kind of thing that can be taught via a PM either.