Thanks for the reply. The fault is now resolved. For those familiar with Worcester/Bosch systems it was fail point D. For some reason the link was missing. Everything working fine as it should now. Thanks again.
JH.
I have a Worcester 28CDI which works no problem for the hot water. However the central heating won't fire up. If I tweek the central heating adjustment on the rear of the PCB then it fires for 30 secs to a minute before cutting out. Tweek again and it works 30 secs to a minute before cutting out...