In message , Oliver Payne
writes
We've got a Worcester 350 Combi (natural gas) boiler, which I think is
about 10-11 years old. The problem is that intermittently, it fails to
fire.

When the hot tap is turned on or the heating is switched on, there are a
few (relay-like) clicks, the fan starts up and then the spark starts.
After a few seconds it gives up and there is another relay click. The
fan stays on, but there is no flame. This only happens about 1 time
every 4 or so; so it's just a minor irritation at the moment.

I'd be most grateful for any ideas on what the problem is, and if it's
likely to be a DIY job. Even if it's not, it would be nice to know
what's wrong if I have to call a heating technician, and how much it
might cost.


Had exactly the same problem last winter.
Stripped it down and cleaned it (not that it was very dirty) and
measured the gap from the spark electrode to the surface of the burners
and set it the mid point of the range in my handbook.
Its worked fine ever since.


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