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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.
 
How did the Electrician test for earth leakage?
 
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
 
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.
 
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.
 
Did he not use a clamp on ammeter (with miliamp setting) at the boiler
 
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.
 
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.
 
It still could be the boiler control board throwing up a fault. Did the sparks test earth leakage at the consumer unit tails?
 
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?
 
(fuse box)The large single cables at the meter position going into your consumers unit (fuse box)
 
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.
 
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.
 
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
 
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
 
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.
 
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?
 

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