I finally got a plumber round to look at my failing gas boiler.
Basically system fires up, then when it reaches required temperature it cuts
out - pilot and everything. There is nothing wrong with pilot, thermocouple
etc and I checked the circuit boards.

Just looking at it, he told me that the fault was the gas valve which would
need replacing. Of course, like all his brethren, he is too busy to do this
in the next month or so, but he said it is something I could do myself.

So, is he likely to be correct in his diagnosis?
Is he right to suggest that this job could be done by a competent DIYer?

thanks in advance for any response

Stony