It was the temperature limit sensor (part no 248079) which is on the hot water feed pipe to the left as you look in to the boiler. The old one didn't have contact paste either so I didn't use it. There was no mention in the manual.
It has been nearly 12 months since this problem happened with no problems during the year. I usually leave the temperature dials at the "6 o-clock" position but as its been so cold lately I turned the CH up a bit. I ran a bath last night and it tripped again and I had to wait about a minute before it would reset. Please see http://uk.youtube.com/watch?v=Oi2kLzxHJQM to show what happens when it has just died.
I am convinced its a temperature thing because I have turned the CH temperature dial back to its normal place and it has been OK. You will notice on the video too that I have used a pencil mark to indicate the maximum I can set the DHW dial to. This is how I seemed to have solved the problem or at least prevented it from cutting out last year.
May there be a problem with water pressure as we only have 15mm going to the bath?
Please see the previous posts as ther are other questions answered there too.
Thanks.
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