Hello Paul, (paul52446m) I was experiencing this problem - I want to verify your point of 1/2" around Thermopile. My Thermo Pile and Coupler are 1/2" away from Pilot and Gas intake. Pilot is always healthy and when burning, fire is as well. Do you mean with Pilot on, the flame should touch and scorch the coupler and pile always? They are. When the flame is on, the Pilot barely reaches either coupler.
My problem was the gas feed was not coming on when using the external wall switch. Five or six attempts without heatilator, the feed would come on and then die after two minutes.
Your answer will help me determine if Thermo Pile and Coupler are deteriorating or I have more trouble shooting to do.
I suspected overheating but I was/am not sure. I suspect not because this is direct vent and the wind, if anything could blow out the flame. In fact with the glass off, the flame and pilot are blown out on a day like today. I did not see any adjustment screws and feel lucky I did not find adjustment screws because I would have definitely played with them.
The fireplace ran for hours around Thanksgiving. We operated rarely. Then week before Christmas I started the fireplace and could not get it run over several days/attempts for more than 2 minutes. I cleaned thermopile then thermocoupler.
Current status, after cleaning, checking connections. I turned it on without glass, wind blew it out twice. Put the glass on and it ran for two minutes and died. Then I turned of the external wall switch, turned it back on after 30 seconds. The fire has been burning for 30 minutes.