baxi bermuda 552 pilot trouble

[dellboy25]

The pilot lights up but after keeping finger on button for a while it then goes out after release. BACKBOILER
have changed thermocouple but problem persists.
what else keeps the pilot on? would i have trouble with the gas valve ?
or could it be the thermostat ?
Its a BAXI BERMUDA 552 Backboiler with fire front.
any help would be apreciated,thankyou.
THE VALVE is honeywell type with grey pusbutton

 

[namsag]

Providing the pilot is heating the tip of thermocouple correctly it is the gas valve thats at fault Corgi guy req

 

[Slugbabydotcom]

A loose or badly fitted thermocouple nut where it connects to the gas valve can also be a problem. Rare though this is. It does happen