We have had this boiler about 5 years. Last year we had a problem in that when the water and heating came on together in the timed mode, after half an hour the heating goes off. We have had two new three port valves fitted and the plumber has been back numerous times (albeit obviously 'fitting us in') when he was here all seemed to work normally but then he was only here for a short period of time on each visit. We still have this problem - yesterday we bought a new programmer - we thought this was the answer as it worked ok last night. Not so this morning, HW and CH come on in the timed session and after a while the boiler stops firing - the only way we can get it to fire again is to turn the boiler off at the wall, wait a couple of seconds and then turn it on .....obviously this is re-setting the boiler each time. When we have the CH on all day everything is fine - it does only appear to happen when the HW comes on too ........any suggestions ???