Boiler & RCD Issue

[parin]

Long time reader, first time poster..

I have been having some issues with my RCD circuit / boiler.

I have a Worcester 24i Junior Combi Boiler installed and when I have it set to 3 on the boiler there are no issues, but when I change it to anything above it trips the RCD.

I called an electrician to test the circuit for any earth leakages but his testing equipment showed everything is ok, he also tested the RCD and there were no issues.

I called the plumber who installed the boiler who could not find any issues.

I called Worcester who replaced the fan, the pump and various other components and it is still occurring. The final time the RCD tripped when the engineer was here, it would not come back on so he removed the fuse from the fuse spur but the RCD would not reset. It only reset when I unplugged all of the the appliances in the flat.

Because of this the engineer seems to think there is a wiring issue, but I'm unsure what to do because the electrician said everything was ok.

Has any one had experience of this in the past, or if can anyone offer any advice it would be most appreciated.

Thanks.

 

[Pete999]

How did the Electrician test for earth leakage?

 

[camerabloke]

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

 

[parin]

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

I unplugged everything in the flat and ran the boiler and it still tripped the RCD.

That time the RCD would not reset until I turned the boiler off at the fuse spur, as soon as I turned it back on (no heating on) it tripped the RCD. I waited 5 minutes and then it worked ok.

 

[parin]

How did the Electrician test for earth leakage?

He plugged something into the circuit and it gave back a reading which he said was very good. He also tested the RCD, via something that was plugged in. It tripped it four times and gave a result which was ok.

 

[Pete999]

Did he not use a clamp on ammeter (with miliamp setting) at the boiler

 

[parin]

Did he not use a clamp on ammeter (with miliamp setting) at the boiler

I think he did that too, I can ring him to ask. He was here for a couple of hours doing numerous tests!

 

[MDJ]

Probably a faulty fan in the boiler, it may leak excess amperage when it kicks in and combined with the contacts and electronics may exceed the RCD rating.

 

[parin]

Probably a faulty fan in the boiler, it may leak excess amperage when it kicks in and combined with the contacts and electronics may exceed the RCD rating.

The engineer replaced the fan and the associated wiring. The only thing that wasn't changed in the boiler was the control panel.

 

[MDJ]

The engineer replaced the fan and the associated wiring. The only thing that wasn't changed in the boiler was the control panel.

Fair enough, can't be that then, worth a shot.

 

[camerabloke]

It still could be the boiler control board throwing up a fault. Did the sparks test earth leakage at the consumer unit tails?

 

[parin]

It still could be the boiler control board throwing up a fault. Did the sparks test earth leakage at the consumer unit tails?

Apologies, but where would the consumer unit tails be?

 

[Pete999]

(fuse box)The large single cables at the meter position going into your consumers unit (fuse box)

 

[parin]

(fuse box)The large single cables at the meter position going into your consumers unit (fuse box)

Oh ok, yes he checked everything in the fuse box.

 

[itselectric]

A long shot here, you could have a cable touching a pipe.
when you are putting the heating on the pipes expand and if there is a cable touching eventually the insulation would be worn away. when the pipes cool down they probably would clear themselves. putting he heating higher would cause the pipes to expand further and possibly make the pipe press further onto the cable. You could find out if this is the cause by having the circuits tested at the moment it trips.

 

[parin]

A long shot here, you could have a cable touching a pipe.
when you are putting the heating on the pipes expand and if there is a cable touching eventually the insulation would be worn away. when the pipes cool down they probably would clear themselves. putting he heating higher would cause the pipes to expand further and possibly make the pipe press further onto the cable. You could find out if this is the cause by having the circuits tested at the moment it trips.

I will try this.

I will also try to the turn all the rads down to zero and if it works for a period of time, I will turn them on one by one to see if that finds the fault.

 

[Lucien Nunes]

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).

I am more inclined to wave a finger at the boiler, but this is where we start to need numbers. The sparks said the leakage was fine, but what was the actual current in mA? What was the change in current when the boiler FCU was switched on? This is important, to distinguish a) something that is about to trip and then trips when the boiler just pushes it over the threshold, from b) something that suddenly goes wrong and causes a major fault. Knowing the background leakage would help with this.

Consider also an N/E fault on the C/H circuit downstream of the FCU, that makes it more sensitive to load on that circuit and prevents it happening when the D/P switch in the FCU isolates it. Did the sparks do any insulation tests on the C/H wiring itself?
Other

 

[snowhead]

I suspect a neutral fault at the boiler.
Is the boiler new and if so was the fused spur replaced / installed at the same time?

Did the electrician remove the fused spur from the boiler and inspect the connections?

As well as pipes expanding more, running the boiler at a higher temperature also means the boiler and pump are running longer

 

[parin]

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).

I am more inclined to wave a finger at the boiler, but this is where we start to need numbers. The sparks said the leakage was fine, but what was the actual current in mA? What was the change in current when the boiler FCU was switched on? This is important, to distinguish a) something that is about to trip and then trips when the boiler just pushes it over the threshold, from b) something that suddenly goes wrong and causes a major fault. Knowing the background leakage would help with this.

Consider also an N/E fault on the C/H circuit downstream of the FCU, that makes it more sensitive to load on that circuit and prevents it happening when the D/P switch in the FCU isolates it. Did the sparks do any insulation tests on the C/H wiring itself?
Other

Thank you, I will look at all of the wiring around the pipes.

What confuses me is that it works perfectly if I keep the setting under 3.

 

[Lucien Nunes]

That is one of the reasons to suspect damaged cables, because the hotter the pipe (or whatever) to more it will expand and press on the damaged insulation. It is still a long shot! It is also a reason to suspect the boiler, pump or MVs, all of which are more likely to have insulation breakdown the hotter they run.

There is also a possibility that a thermostat is changing over at a certain temp, and completing the circuit to the fault. Whether it is a room stat, pump overrun or whatever, there might be some clue in the time lag between the temp rising and the RCD tripping. How long after turning the boiler up beyond 3, did it take before the trip occurred?

 

[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: