I have changed the thermocouple, made sure the boiler was clean and
checked the jets. However none of them seems to of helped. I have
managed to get the pilot to hold once but when I have then switched
the CH on it just clicked and the back boiler didnt come to life.
Before when the CH was switched on there would be a sort of whooshing
noise then the back boiler would ignite. I dont know what to do next.
I have also searched the net for spares for the make of back boiler
but to no avail, can any one help me here, please.

Thanks for your help so far gents.

Look forward to your response.

Craig