Baxi Solo 2RS - pilot light won't stay lit?

I've the same problem on my Solo 2 50 RS, called a "gas fitter" in 10 weeks ago, first he changed the thermocouple (universal one did not fit), then he changed gas valve and it worked. This week same problem has occured. Called fitter back but he's at the limit of his capability and doesn't return my calls.
Naked flame placed under the thermocouple will fire the boiler up.

JRF
October 2008

Loose thermocouple
Thermocouple us
Gas valve

ivor
October 2008