Non-motoring > Central Heating Timer Blowing Fuse Miscellaneous
Thread Author: zippy Replies: 7

 Central Heating Timer Blowing Fuse - zippy
The clock works fine until the central heating comes on (heating or water) then the fuse blows.

It's a right pain to access the plug as it's behind a cupboard in the utility room and the space is made for elves.

So I'm thinking there's a fault with either the new 3 port switch or new pump that was fitted about 3 weeks ago.

I had noticed a lot of start up rattling from the system if it went off for the night.

The plumber cleared out a lot of gunk from the system but I'm wondering if more gunk is blocking the pump, causing it to stall and blow a fuse.

Any ideas please?

 Central Heating Timer Blowing Fuse - RichardW
Unlikely the pump would blow the fuse even if it was stalled, and the valve shouldn't either, since it exists in the stalled state most of the time. Possibly a wire has come loose and fallen where it shouldn't or some water has got in where it shouldn't be! Have you got a multi meter? Can you access where the pump and valve were connected, you might be able to disconnect them one at a time to see if that stops the fuse blowing. Assuming this is a system with an external pump, then the boiler won't run for long without tripping on overheat if the pump is not running, but it could prove a point.
 Central Heating Timer Blowing Fuse - Zero
I have had stalled pumps, and they dont blow fuses.

Thats not to say the new pump is not faulty tho the windings could be defective. The way to tell if its just the pump, is the manually move the three way valve lever to activate the pump, if it blows right away then you know its in the pump part of the circuit.
 Central Heating Timer Blowing Fuse - maltrap
Is the fuse the correct rating ?
 Central Heating Timer Blowing Fuse - percy
Is the pump separate from the boiler? Can you disconnect the mains supply from the pump and try again? If the fuse doesn't blow then.... it's the pump. Dont let the boiler fire up without any circulation. Many modern pumps are 'clever' and have electronics on board and may be prone to early failure...... For info, the fuse should be 3 Amp maximum. Good luck!
 Central Heating Timer Blowing Fuse - zippy
Thanks for all of your tips.

I spent a fun day yesterday off work and isolating the pump, 3 port valve and got nowhere.

Mrs Z got fed up and called a plumber from a local firm. According to the website we got the foreman.

He could not figure out what was wrong for a short while as the circuits were testing fine.

Then he found the problem. A power cable to the boiler was routed around a hot part and melted exposing the core which shorted.

8 inches of cable removed, replaced and rerouted and a £111 bill for an hour and a half’s work.
 Central Heating Timer Blowing Fuse - percy
Glad to hear your problem is sorted out. I wonder which 'qualified' engineer 'installed' the cable? Guess we'll never know.....
 Central Heating Timer Blowing Fuse - maltrap
Glad you got it fixed, sounds like money well spent.
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