how do i fix my potterton netaheat 10-16 Mk 11?

I have just spent 400.00 pounds getting a new hot water cylinder fitted and a new motorised valve aand a considerable amount of time draining the system down and flushing the radiators out. the boiler lights up for about 1 min then the gas cuts off. the pump is rumming but i cant get heat or hot water. Is it the thermocouple in the boiler ?