Boiler & RCD Issue

[parin]

The pump has been changed as has the fan so I'm not sure if it's that.

I also disconnected the thermostat so it is running all of the time as long as the boiler is on and it had the same result.

If it is on 3 I and I turn it up it takes around 10 mins to trip, and it takes the same time it it's done from a cold start.

 

[itselectric]

I have seen exactly this fault. C/H would fire up and about 5 mins later the lighting circuit would trip. Long straight run of copper pipe, expanding a few mm and pressing on a cable that was laying beside it in a joist notch. A long shot I agree but possible. In this case, though, it would have to be one of the heating system cables, because the tripping occurs when the heating system FCU is on and not otherwise (e.g. post 4).

Lucian, he does say RCD trips so it could be affecting any circuit.

 

[R G]

The only way you are going to find this fault is by unplugging / isolating every thing in the property , Main Switch off and by pass the respective RCD (temporary) Main switch back on then switch on the boiler bring it up to temperature , using a clamp meter that measures in MA on each off the CPCS in turn ,bear in mind no other person is to use any equipment in the property whilst doing this , you can then trace this back

 

[Lucien Nunes]

Lucian, he does say RCD trips so it could be affecting any circuit.

But he says that turning the heating FCU off stops the tripping and it can trip instantly when you turn it back on, even before the boiler fires up. So this suggests the FCU is isolating the fault, i.e. it's in the heating wiring.

using a clamp meter that measures in MA on each off the CPCS

If the fault is to the heating pipework or boiler casing, this probably won't find it, as most of the current won't be going through the CPC. Much better to measure the difference in the L&N, which is after all what trips the RCD.

 

[R G]

Agree , this might not find it , its a difficult one this as it could be going back through the casing as you say , I would eliminate all other possibilities though with other wiring on other circuits though , I suppose you could throw out a temporary supply from the consumer unit just to supply the boiler on its own , with all other circuits isolated

 

[johnsparks23]

Consumer unit tails: the two thick grey cables, that supply the consumer unit, from the meter. Line & neutral.

 

[parin]

Agree , this might not find it , its a difficult one this as it could be going back through the casing as you say , I would eliminate all other possibilities though with other wiring on other circuits though , I suppose you could throw out a temporary supply from the consumer unit just to supply the boiler on its own , with all other circuits isolated

I disconnected the cooker and used an extension lead to supply the boiler and it had the same result. I also isolated all other circuits on the rcd whilst I tested it.

the circuit would also not reset until I unplugged the boiler.

I've called Worcester again and they are coming out on Wednesday.

Fingers crossed.

Thanks everyone for your help so far

 

[GLENNSPARK]

It's one of the items you unplugged. Try plugging in one at a time and turning on and see if it trips the RCD

is it?

ever heard of a neutral-earth fault?

 

[cobrauk]

Is the boiler circuit direct from the consumer unit or part of another circuit ?, is it a rcd or a rcbo that is tripping, if its the main switch then it will be a rcd if its replaced the mcb it will be a rcbo

 

[parin]

So I put the boiler on a non rcd circuit and the rcd still tripped when the boiler was put on anything above 3.


I'm guessing one of the pipes is causing the wiring to heat up and trip, now it's just a case of finding it!


The sockets are on a ring circuit, is there anyway to isolate one room at a time so narrow down where the issue could be?

 

[Orry Clayton]

It would be much easier for you to follow the heating pipes of the boiler.

Orry
HE Engineers Ltd

 

[Lucien Nunes]

We seem to have some conflicting evidence. In posts #4 & #27 the fault appears quite certainly to be in the heating wiring, because switching off the FCU (#4) or unplugging the C/H system (#27) immediately stops the tripping, reconnecting it can cause an instant trip (#4) even without the boiler firing. Now you have moved the C/H circuit to a non-RCD CU way and the behaviour hasn't changed. At least one RCD-controlled circuit must be faulty, which can't be the boiler wiring.

Putting the two together, how about a cross-connection between the boiler wiring and another circuit, such as borrowed neutral that passes current when a stat changes over or thermally-triggered short? Well, then we have the conundrum that when the two circuits were both on the RCD originally, then unless there are multiple faults (involving a live from each circuit and a CPC) the original fault would not have caused a trip.

So it's looking like either one or more of your observations is wrong, there's a general snarl-up somewhere, or there might be two separate faults, one on a circuit that is still RCD-protected and the other a cross-connection, borrowed neutral etc. on the C/H wiring.

I fear you are going to have to get real test results to take it further without a whole load of possibly dangerous trial and error. I would be tracing strategically with a leakage clamp, insulation tester etc, taking in certain permutations (e.g. N-N between circuits) that a routine quick test would not. I would also by now have disconnected all the heating wiring from the boiler and meggered the hell out of it!

 

[UNG]

I think this is a troll

Gets an electrician in to check out the wiring in the first post then in later posts appears to be doing the electrical work himself

 

[Octopus]

So I put the boiler on a non rcd circuit and the rcd still tripped when the boiler was put on anything above 3.


I'm guessing one of the pipes is causing the wiring to heat up and trip, now it's just a case of finding it!


The sockets are on a ring circuit, is there anyway to isolate one room at a time so narrow down where the issue could be?

If and when you get a spark in, tell them what you've been doing!

Madness.

 

[Rockingit]

Shall we eliminate some possibilities?

1. Heat... well, on a modern boiler a rad loop tends to run (maxed out) at no more than around 75C, and a DHW feed at around 65C as they leave the boiler... neither of which temperatures are going to cause a cable, or a 15mm copper / plastic pipe many issues, even if they were touching side by side.

2. OP - as you paid for an electrician to come in and do some tests, he should have left you with some paperwork - post it up.

3. If a Worcester engineer, who only ever in his life sees and touches Worcester boilers and knows each part individually by his pet name for it, say's it's not their kit at fault, I'd be inclined to pay attention to it.

 

[Geordie Spark]

Shall we eliminate some possibilities?

1. Heat... well, on a modern boiler a rad loop tends to run (maxed out) at no more than around 75C, and a DHW feed at around 65C as they leave the boiler... neither of which temperatures are going to cause a cable, or a 15mm copper / plastic pipe many issues, even if they were touching side by side.

2. OP - as you paid for an electrician to come in and do some tests, he should have left you with some paperwork - post it up.

3. If a Worcester engineer, who only ever in his life sees and touches Worcester boilers and knows each part individually by his pet name for it, say's it's not their kit at fault, I'd be inclined to pay attention to it.

Mine is running at 80 degrees C on the flow leg (as it leaves the boiler) and can - if I wind it up - reach 90 degrees C .. so there !! nernernenerner!! :ciappa: