Boiler / Ring ?

[DerbyMercx]

I'd appreciate any advice on this.

Our combi boiler has been tripping the RCD occasionally for about a month - this has become more frequent - and it trips it with all electrical appliances in the house unplugged and it never trips with the boiler off so I'm more or less certain it is the boiler that is causing it.

Boiler was due for a service so asked boiler engineer to have a look and he couldn't find anything wrong and suggested an electrician. Called an electrician who couldn't find anything wrong - he said the earth was a bit high at 1.5ohms (I don't really know what the significance of that is) but the only thing he could suggest was wiring the boiler so it bypassed the RCD. Now because the boiler is on a spur of the ring main with it's own switch and 3 amp fuse (electrician said this was an unusual set up) all the sockets bypass the RCD. He didn't seem concerned by this but I'm just wondering if the RCD is there for a reason whether that is really a safe way of doing things ?

Both the boiler and the house wiring are less than 3 years old.

Any advice ? My gut feeling is that at the least the boiler should be wired directly to the consumer unit with it's own trip switch and the sockets be put back on the RCD. Is it even safe to run the boiler if it is tripping the RCD ? Is having a boiler wired to a spur a poor way of doing things and if so why ?

But I don't normally touch electricity or gas and having had the professionals in don't really have any definite knowledge to go against what they've done.

 

[rebuke]

Did your electrician test the RCD specifically (he should have plugged in a test device which would have caused the RCD to trip several times), as it could just be a faulty RCD that is triggering on a very small level of earth leakage, rather than the expected 30mA.

The ring main should NOT be wired to bypass the RCD - the wiring regulations require that all general purpose socket oulets should be protected by an RCD, so moving the ring to the non RCD side is not a valid option.

It's fairly normal to wire a gas boiler/heating system as a spur off a ring main, I don't see why the electrician said it was unusual - given you imply he recommended moving the sockets off an RCD, I wonder how good an electrician he actually is...

Assuming the RCD is not faulty, then if something is causing it to trip there must be a fault - from what you describe it does sound like the boiler (or at least some part of the heating system, e.g. a thermostat or whatever). Unfortunately, these sort of intermittent faults are always hard to find. Can you think of any pattern, e.g. does it only trip when the heating comes on / thermostat calls for heat etc etc, as that may narrow down which component is at fault.

 

[flameport]

The sockets are on an RCD because this is a requirement - under the current 17th edition regs, all socket outlets must have an RCD, and the previous 16th edition stated sockets likely to be used for outdoor appliances must have one.

Removing the RCD because it trips often is NOT the correct solution.
If the boiler is causing the RCD to trip often, there is something wrong with it. (could be the boiler itself or the pump, controls, wiring, valves, etc).

Boilers on a spur from the socket circuit is very common.

You need the RCD back on the socket circuit. As for the tripping, the fault needs to be found and repaired.
Putting the boiler on its own circuit could be done, but if there is a fault it needs to be fixed either way.

 

[DerbyMercx]

Did your electrician test the RCD specifically (he should have plugged in a test device which would have caused the RCD to trip several times), as it could just be a faulty RCD that is triggering on a very small level of earth leakage, rather than the expected 30mA.......................
.................
Assuming the RCD is not faulty, then if something is causing it to trip there must be a fault - from what you describe it does sound like the boiler (or at least some part of the heating system, e.g. a thermostat or whatever). Unfortunately, these sort of intermittent faults are always hard to find. Can you think of any pattern, e.g. does it only trip when the heating comes on / thermostat calls for heat etc etc, as that may narrow down which component is at fault.

Thanks - that confirms what I felt about it not being a correct fix and not to leave it like that.

I don't know if he tested the RCD.

The boiler can function OK for a day but then start to trip every few minutes or so - once it starts tripping it pretty much has to be turned off for a long period before you can get any hot water or heating without it tripping frequently.

It is most likely to happen when the heating is on and then you turn a tap on - so I suppose when it is asked for most power. However it isn't always turning a tap on that causes it to trip - sometimes it trips just when it is powering the central heating. If you have the boiler on but not the heating and aren't running a tap then it never trips - so I suppose just when it's asked to actually heat something up would be the simple answer.

So the way to go now would be get someone who can first test the RCD - then rewire the unit so the ring is back on the RCD and then EITHER fix the problem with the boiler OR given that nobody I've had in can find a problem with it, maybe wire it separately to the consumer unit - or should the boiler always be protected by the RCD ?

Thanks again.

EDIT - cross post - thanks for the above - will get on to that.

 

[david_uk]

The reason boiler feeds are often wired as a separate circuit are to avoid this problem - any fault will trip out the sockets unnecessarily. You don't HAVE to put the boiler on an RCD, but there is no option with the sockets. However, although you don't have to, the way houses are wired in twin & earth with drops in capping or plastic conduit means you will most likely need to have an RCD on it to comply with 17th edition regs.

My suggestion would be to have a separate circuit protected by it's own RCBO. That way any tripping should be limited to just that circuit. However, the problem you have isn't normal. Boilers should normally work without tripping this much. Does it trip when the motor kicks in? Old and tired motors in any appliance can cause tripping.

Obviously any additions or alterations to the wiring may well be notifiable - deffinitely in a kitchen.

 

[sparkyspike]

The electrician gave you very bad advice. Even under the 16th edition, all socket outlets for portable equipment were required to be RCD protected, regardless of whether they were for outdoor use. So do not remove the ring from the RCD. Get someone in who knows what they're doing. They need to test the boiler itself, the RCD and also correct the high earth impedance.