my robinson willey gas fire keeps going out after 15 to 20 muinits i hear a click then a sound like a flame being blown out then the fire is out and i have to relight it.
very unusual for a thermocouple to run for 20 mins then go out, you usually cant get the fire to light at all if the thermocouple has gone. you haven't said what type of fire it is but id be looking at the pilot flame being blocked, get an engineer in and get the fire serviced properly.