Fuse blowing next to central heating clock

[pms1cmr]

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.

[Andrew Gabriel]

Water leaking in the boiler, or from the pump, or in the electric valve(s). Don't keep bumping up the fuse value though. That just makes a bigger mess of the fault site, and might cause further damage elsewhere.

[David Hansen]

On Tue, 28 Aug 2007 03:07:36 -0700 someone who may be [e-mail] wrote this:-

The fuse blowing is trying to tell you something. Find out what it is, rather then hoping for the best.

In addition to the water suggestions, perhaps a cable or bit of equipment is damaged.

Someone with more experience could measure and work out where the fault is likely to be. In your case if a visual inspection doesn't reveal anything it is time to employ someone to find the fault.

[Roger Mills]

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.