Electrical problem with gas CH

Good evening all, I have a bit of an electrical problem with my very old conventional, fully pumped, vented, gas CH system.
Woke up this morning to no electricity in the house. Check CU and find main breaker tripped. Reset this and all ok. Tripped out again at lunchtime, same procedure and all ok.
Late this afternoon it tripped again and would not be reset.
By trial and error I have found that the fault is definitely in the gas boiler wiring.
Switched all off at the programmer. Try the DHW - drain a load of hot water - boiler fires up, no problem there. Turn DHW off. Try CH with roomstat turned down - no problem
- turn room stat up to call for heat - electricity trips out.
Am I right in thinking that the problem probably lies with either the roomstat or Danfoss CH motorised valve? Unfortunately the wiring for both is subfloor. Roomstat wiring is totally inaccessible, CH valve can be got at with a grovel.
I don't know how to test either. Any thoughts or other suggestions for a remedy would be much appreciated.
TIA
Nick.
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Worth disconnecting the pump and see if the RCD holds. Check that the power is at the three core cable at the pump while it is disconnected.
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Hi You say system is fully pumped so pump should run when DHW is called for ,as you say this does not trip the breaker you can rule out the pump as long it is proved running. If you can access the motorised valve find the manual activation bar (flat piece of steel protuding from 1 end.) This should move (wear gloves can be very hard on fingers as it opens the valve) ,once fully open pull up towards underside of valve and release and it will lock open. Now fire up on DHW only setting and see if CH warms up or breaker trips. If breaker trips wiring to tank stat may be faulty if not suspect room stat or motorised valve. HTH CJ
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writes

The boiler's not a fuelsaver is it by chance?
--
geoff

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On Thu, 10 Feb 2011 21:54:25 +0000, geoff wrote:

Why would that fault on CH not DHW?
(Not saying it couldn't, just curious why you suspect this?)
--
John Stumbles -- http://yaph.co.uk

Teenagers: tired of being harassed by your stupid parents? Act now! -
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writes

You're making the fundamental error of assuming that I read the whole of the thread
Just checking ...
comes down to whether it's a dual path primary heat exchanger or whether it's a HE / calorifier where the pump is only active in DHW mode
the OP didn't mention the make / model of boiler ...
--
geoff

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On Wed, 09 Feb 2011 18:22:36 +0000, Nick wrote:

Could test roomstat by removing it and connecting together the wires that would be connected when the stat is calling for heat.
But I'd suspect the motorised valve given (a) that it brings together water and electrickery (b) sod's law.
--
John Stumbles -- http://yaph.co.uk

It's bad luck to be superstitious.
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Sounds like you might have been struck by the switchover problem described in www.bbc.co.uk/i/y92mb/ :-)
The rest strikes a chord for some in this group too...
--
John W


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Weston" wrote:

Sorry, episode 1 has now gone...
--
John W


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