central heating tripping rcd

monkey5 · Sep 25, 2009

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

betty swollocks · Sep 25, 2009

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

monkey5 · Sep 25, 2009

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

NozSpark · Sep 25, 2009

I'd have a go at IR testing the pump or valves...

Revved Up Sparky · Sep 26, 2009

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.

SPECIAL LOCATION · Sep 26, 2009

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!