Power Surges



I wondered if any experts on here could shed any light on this problem I had today:

Called out to a breakdown yesterday. Fuses blowing.
Found the Switchmaster Vlv Head to be the culprit, so cut the wires to the head. Rewired in a junction box so all wound fire, and moved the vlv body into the mid position.
Turn on, boiler and pump work & 30 seconds later fuse blows again. Oh dear me thinks...more than 1 fault here.
Whilsh Im in the airing cupboard, I took the live out of the pump and tried again. All fires, so I can get the h/w around on gravity and a upstairs tepid at best.
I leave, knowing Ill be back today to replace pump & m/vlv.

So today, replace faulty parts, turn on and nothing (the rewire from the switchmaster to honeywell was easy to work out) and the fuse blows.

I remove the programmer and link out with trusty insulated thin nose pliers.

Hey presto all works, so bypass the programmer, turn on for 15 mins approx to clear air etc. Turn the fused spur off and POP. Fuse blows.

Replace fuse, turn on...all fine. Switch off and POP. There goes another.

Isolate boilers power supply on the fused spur turned on, then off, then on, then off. Fine. So realise the capacitor on the live side of the stat may be a problem. So...cut the live.

Now all works for 15 mins with me doing everything...on off on off on off.
Then POP. Cut the neutral to it and now all seems fine.

I checked all components to see if they went to earth and done all the basic electrical checks.

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