Intermittent hot water problem on a Glowworm Hotwater Express 100

I have a Glowworm Hotwater Express 100 combi boiler which according
to the label stuck to it was probably installed in 1993. The boiler
has developed a problem where the boiler doesn't fire up when the hot
water taps are opened. Occasionally, the boiler will work but now it
seems that the problem has got worse. The boiler emits a series of
clicking noises when the hot water tap is open and the boiler hasn't
fired. My wife noticed that she can get the boiler to fire by hitting
it! Obviously, this is not a long term solution and once that I fear
may even damage the boiler further. I had a plumber in and his initial
thoughts were that the diverter valve was sticking. Later, he said
that after discussing it with colleagues, he's not so sure and he's
not keen in replacing it only to find out that the problem is still
present. Does anyone have and ideas what could be the problem with the
boiler? Thanks.
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I had a similar problem with my Glowworm combi (which must be 15+ yrs old) recently. There were a few dry joints on the pcb that I resoldered. It's behaved perfectly since (excluding the thermocouple that I had to replace today...)
Reply to
Darran Ames
In message , Rick writes
Either the diverter valve or the PCB
If the CH fitter isn't sufficiently competent to work out which it is, get someone in who can
Not sure offhand what the clicks are though, I'll probably realise later
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