In an earlier contribution to this discussion,
wrote:

Hi,
I'm a bit of a novice so please bear with me.

The fuse in the fusebox next to my central heating controller keeps
blowing. I replaced it twice yesterday with a 3A fuse and again this
morning with a 5A fuse and within half an hour of the heating coming
on and the radiators just starting to get warm it blows.

Has anyone got any ideas as to what the most common causes could be.

For info, it's a conventional boiler (not combi). It's a fairly old
Glo Worm system and it's a normal (not digital) mechanical clock that
it operates from.

You have an electrical fault which is causing current to flow from live to
earth. It's probably variable and intermittent in nature, but when the
leakage current exceeds the fuse rating, the fuse blows.

The fault could be at any of a number of locations in your system, but I
would start by having a critical look at the pump - that is the most likely
culprit in my experience, because that's where water and electricity come
closest together. If you feel competent, you can test it by disconnecting
its existing wiring and wiring it to a 13A plug with a 3A fuse in it. You
can run the pump without the heating being on, as long as there's water
going through it. If that fuse blows, it will confirm my suspicion - and you
will need to replace the pump.
--
Cheers,
Roger
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