central heating tripping rcd

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had a call out tonight to a house that had lost all power to sockets, cooker garage etc, turns out rcd had tripped and obviously cut 5 circuits, got it down to down stairs socket circuit then narrowed it down further to be the fcu which powers the central heating and hot water timer, did a few checks no trapped wiring no nicks no water and couldnt find anything wrong, so said i would go and have an another look tomorrow as it was 10 at night. any suggestions what it could be as im not sure what it can be as checked everything i could think of. i did also fit a new fcu just in case it was that but still tripped, i also disconnected the timer feed from fcu it didnt trip so definitely something to do with Central heating wiring somewhere. there have been no modifications or works at all. any help would be appreciated.

cheers wayne

 
i had a similar job a year or so ago, the supply cable to the boiler, normal 3core flex, had been resting against the inner panel and the heat eventually had burned through the outer sheath and then the neutal conductor which tripped the rcd, as you said disconnect the fcu or timer and rcd set, might be worth a look

 
i had a similar job a year or so ago, the supply cable to the boiler, normal 3core flex, had been resting against the inner panel and the heat eventually had burned through the outer sheath and then the neutal conductor which tripped the rcd, as you said disconnect the fcu or timer and rcd set, might be worth a look
yeah its 3 core flex. i disconnected the fcu and timer tonight and it didnt trip. will check the flex tomorrow cheers for reply

 
I would disconnect the supply from the FCU at the boiler end and then do an IR test on the supply cable. If the test reads clear then reconnect and then try running the boiler with the external controls bypassed. If all is well then proceed to fault find on that control circuit. If the boiler still trips the RCD with supply cable IR clear and external controls bypassed then the boiler must have an internal fault which may need to be referred to a heating engineer.

 
could also be a water leak somewhere dripping into a badly positioned joint box?..

heating / water comes on, valve or pump leaks a bit..

water trips RCD..

then water dries up...

You test all seems fine cuz intermittent fault now gone! :(

 
Probably pump or motorized valve gone generally what you find. Do an insulation test L&N to E at 250v and see what reading you get.

Batty

 
How did you get on monkey5 - my guess syncronus valve faulty.

 
hi, i keep meaning to post my finds, it turned out to be the pump faulty got it changed all spot on now. thanks for everyones suggestions

 
hi, i keep meaning to post my finds, it turned out to be the pump faulty got it changed all spot on now. thanks for everyones suggestions
They are the usual ones then valves. Glad its sorted.

Batty

:)

 

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