Reply With QuoteI’ve just been through this and it was traced to an external light with an IR sensor. Moisture was tripping RCD.
The electrician did load testing to find it. Apologies, no idea what load testing is !
A couple of times recently after or during heavy rain, the RCD in the circuit box in our hall has tripped, taking out all of the three-pin sockets. The curious thing is that it seems only to trip when the gas boiler is on. At the moment for example the RCD switch is back in position and, with the boiler switched off, it will stay put indefinitely.
There is an electrical socket on the wall outside and it's possible that water has got into that, because the cover has deteriorated. But while the boiler is off the RCD doesn't trip. Turning it back on while the boiler is on will make it trip within 5-10 mins (until the rain's stopped for a while and presumably something has dried out).
There's no sign of water ingress near the boiler and the flue that comes through the external wall it's attached to is in the same condition it's been in since we moved here in 2009; it has a little rain canopy and that hasn't deteriorated at all.
It doesn't happen at all during dry weather.
Any thoughts, anyone? Is it plausible that a damp external mains socket could make the RCD more sensitive to being tripped by the boiler?
I’ve just been through this and it was traced to an external light with an IR sensor. Moisture was tripping RCD.
The electrician did load testing to find it. Apologies, no idea what load testing is !
Thanks Joe, it's just that the boiler seems to trip it that doesn't seem to fit the hypothesis that it's something exposed outside that's to blame. How much did the electrician cost, if you don't mind me asking?
How old is your boiler? It’s possible it has a fault or that the boiler is using the earth as a switched live if it’s been replaced in situ and that is grounding out (ours was like this, had an RF link put in to reinstate the earth and enable pump overrun).
"Bite my shiny metal ass."
- Bender Bending Rodríguez
He refused to accept any money, he’s a village local and wanted to help. If it helps, I’d say it took him an hour.Originally Posted by monogroover
The boiler's the same age as the house, about 20 years I think. It does get serviced every two or three years. There's definitely been no change to the way it's wired in the last 15 years, but the RCD tripping issue has only happened in the last two weeks.
Could be just a coincidence- I’d swap out that exterior socket asap and make sure it watertight
That then would elimate that
Christ this needs to be not here.
So many comments on investment or lack of over the years.
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Last edited by Mj2k; 5th December 2024 at 07:43.
This might make the circuit more sensitive, especially when the boiler is drawing power.
I'd check the flue too, might be letting water back in which trips the boiler.
Wrong thread?
You might have more than one appliance/socket/wiring junction with a small earth leak which, when all in use, together take the leakage over the limit of 30ma or whatever it is.
Thanks a lot for the replies. There's no problem running fan heaters and a washing machine off the same circuit, but the gas boiler, which I think uses less electrical power than any of those will trip the RCD as soon as I switch the hot water on at the moment. Even with the other appliances switched off.
It's not the consumption that is relevant, it's the amount of earth leakage. If the boiler is leaking 10mA to earth the the RCD won't trip but if the rain fault adds another 25mA this will take the total to over 30mA & the RCD will trip. You need a sparky who can measure the earth currents & find the cause of the rain induced leakage. Outside sockets are always a good starting point.
As you know the external socket has a fault, I see no problem with replacing that for starters.
A gas boiler is also relatively unique in having a high voltage spark ignition (I take it that it does, rather than a pilot light). Something very few other appliances have.
This can be relatively noisey on the earth and therefore trip an RCD if its own earth connection is poor, or if there is other contributory faults (like the possibility of the external socket leaking).
Even if your boiler doesn't spark, your observations suggest that there might be a fault in the boiler too.
So I would guess that one fault on its own was not the problem, but when a second started, the two together make earth leakage big enough to trip the RCD.
You could go through all of this, but a professional will do it better, and quicker as they will have all the right metering kit to isolate the source of the fault(s)
Thank-you - that is a plausible working hypothesis because I can't see how moisture from rain can be interfering with the boiler. For now I've sealed up the cover on the external socket with plastic ties and plastic. I will have it replaced, or isolated in the short term to see what happens.
If water gets into flue will only end up in combustion chamber and this should have gas-tight seal to rest of boiler (and dangerous if not).
This sounds about right to me. Where you have a single RCB covering a number of outgoing circuits the RCB ‘sees’ the cumulative total of earth leakage from all the circuits. It very easy for that cumulative total to exceed 30mA and trip the RCB even when no single circuit’s leakage is bad enough on its own. This is why modern (18th edition) consumer units are no longer split load (half RCB protected and half not) and every applicable final circuit now gets its own individual RCB protection using RCBO or AFDD breakers, meaning the cumulative total is no longer a consideration.
Replace the outside socket, making sure the back is sealed - that's an easy DIY job.
If it still trips then call an electrician to locate the fault.
Many thanks for all the replies, appreciate the help and advice. A heating engineer has replaced a pump that had seized - and the boiler can now be switched on without tripping the RCD. I'm still a bit uneasy about the correlation to the behaviour with wet weather, but there's no doubt that the boiler is working at the moment, it chucked down all day yesterday and there was rain this morning. So I'm hopeful.
The external socket has been carefully waterproofed using plastic sheet and plastic ties and it will be replaced in any case.
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