My thermal coupling lights up,when the timer clicks in,.but the back burner dos,nt ignite,...to heat the hot water. so i cant use the central heating either .when needed. many thanks if some one can help..

Brian, June 2009

what kind of boiler?

Sounds like not a thermocouple but you have a automatic pilot light which ignites but no main burner???

Could be gas valve fault not opening solenoid 2 allowing gas to main burner, could just be recognition of pilot not being found so boiler does not think pilot has lit.
Does it keep clicking/ignition at pilot trying to light although its lit already????

q, June 2009