how can i keep the flame on my boiler alight ???

Is it the correct thermocouple? should be part number402s378 GC no323 427.
How long does it stay on for? If your is the 30/50B then your thermocouple will be the Interrupted type which has the limit stat attached. You can short this out to test only that its not this making your pilot go out.
If you are 100 percent sure its the right thermo couple and the limit stat is fine then its a call out by a corgi reg person to change your gas valve.

MadMoo
November 2007