First check if the pilot flame is enveloping the tip of that thermocoupler.
The thermocoupler end connected to the gas valve can be unscrewed and it's DCMV measured when the pilot flame has been going for a minute. A complete test requires an adapter to be placed between the gas valve and the thermocoupler to measure the DCVM while it's screwed in place.
Fireplace thermocouples are cheap but can often be a very space restricted repair.
The thermocoupler end connected to the gas valve can be unscrewed and it's DCMV measured when the pilot flame has been going for a minute. A complete test requires an adapter to be placed between the gas valve and the thermocoupler to measure the DCVM while it's screwed in place.
Fireplace thermocouples are cheap but can often be a very space restricted repair.
