why does my gas fire cut out?

Highly unlikely to be the thermocouple,if it was the fire wouldn`t come on at all.Much more likely to be a partially choked pilot or possibly even a choked chimney.
My advice is get a Corgi Engineer to Service the fire,this will involve removing it and checking the chimney with a smoke pellet,he should also clean the fire and clean and/or replace the pilot assembly.

Gasman
August 2008

Thermocouple requires replacing. It will get progressively worse and not allow your fire to light at all.
Get a replacement from a boiler supplies outlet. They will need the make and model details of your fire. Depending on the make you may have to take the burner tray out to get at the thermocouple to change it. If your not competent with gas connections or gas safety practice get someone who is.

Cledlyn
August 2008