Boiler tripping RCD

[Sajid.Y]

Hi, I've recently had a Worcester 30i Combi fitted to replace a system boiler. And after a week or so, it tripped the RCD.

I managed to isolate the problem to the circuit the boiler is on, all other circuits would run fine, but the boiler circuit would trip every time, until I disconnected the wiring that was connected from the plug socket to the boilers Fuse switch.

I managed to get the engineers who fitted the boiler back around, but magically when the boiler wiring was connected again it started running, he messed around with the rest of the wiring on the fuse which caused it trip again, but he blamed the wiring on the rest of the loop in the circuit.

Since then it has tripped again, and same thing, RCD did not reset until I disconnected the boiler wiring from the socket, every other plug worked fine on, and when I connected the boiler back out was up and running again.

As far as the fitters are concerned it was running so there's no issue on the boilers side, but that's the only thing that's been added since I moved in over a year ago, and it's only tripped since that's been added.

The boiler has been fitted directly above the sockets and the fuse is running out from that socket.

 

[CBW]

Is it connected to a spur or socket? and do you mean you unplugged it from socket? If it's installed above the sockets they may have nicked a wire with a screw? Could be a loose wire, or a strand touching another.

Get them back, it's their install that's causing a fault.

 

[Sajid.Y]

The boiler is connected to a spur which is connected to a socket.

I pulled out the wires from the socket that leads to the spur, and it's only then that the RCD resets. But once it resets it runs fine for a few days, and as far as they're (the company who fitted it) concerned if it's running they've not done anything wrong and it's the rest of the circuit causing the problem.

 

[CBW]

If it worked fine beforehand it is their issue. Might be best getting an electrician in though, if he can prove it's their fault then send them his bill.

 

[durhamplumber]

Get them back, it's their install that's causing a fault.

Lol.

 

[durhamplumber]

If it worked fine beforehand it is their issue. Might be best getting an electrician in though, if he can prove it's their fault then send them his bill.

So if wiring is crap to start...and a boiler fitter dusturbs it causing earth leakage faults...It is all the fitters fault???? Yeah right.

 

[durhamplumber]

pulled out the wires from the socket that leads to the spur,

Top idea......And you still wish to blame the boiler fitter FFS

 

[durhamplumber]

concerned if it's running they've not done anything wrong and it's the rest of the circuit causing the problem.

Indeed!!!!!..But hey....just blame and sue the boiler fitter for your crap wiring.

 

[ericmark]

To test a RCD we use a special meter, the installer I would hope had the special meter, if the RCD is not faulty then it can be either a boiler fault or a collection of faults, it is hard to pin point if boiler or not without meters, some Bosch Worcester boiler do require a type A RCD but looking at the installation manual it does not seem that model requires it, in fact the manuals I read don't even say it needs a RCD.

The regulations say every installation shall be divided into circuits, as necessary, to reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation. But it does not actually say how big the circuit can be and I have seen where whole house has just 2 RCD's so there is a heck of a lot on each circuit and the result is it can add up.

Over 3.5 mA earth leakage needs special earthing, so the boiler should not allow more than 3.5 mA to earth, however the test equipment to measure that is not some thing the normal house holder will have, if I wanted to measure it my clamp on is not good enough so would need to use my PAT testing machine, but I would think most practising electricians would have a tester that could test that leakage. It is about 65 kΩ which I could measure with my 250 volt insulation tester, the 500 volt range may damage the boiler.

The problem is some how you need to prove the boiler leaks over 3.5 mA and your not able to do that, or of course the reverse and for the installer to demonstrate it does not draw over 3.5 mA to earth. We may be sure the boiler is at fault, but we need to show the boiler is at fault which is a different thing.

The RCD does not measure current to earth it measures the difference between current in the line and current in the neutral wire it assumes if not equal it must be going to earth, however there can be a DC component on the supply which can unset the RCD or spikes on the supply can upset it, and some electronic equipment can trip a RCD due to this. Not all RCD's are equal some can better cope with spikes etc.

But the main problem is normally due to some light powered item having a neutral to earth fault which only shows up when a heavy powered item is used, so often we blame the kettle when the real problem is the toaster. Only way to prove which items are faulty is with meters. Sorry not much you can do DIY wise.

 

[Gasguru]

The boiler installer is highly unlikely to have any equipment capable of measuring earth leakage unless he is also a qualified electrician.

Now assuming he hasn't created a new wiring fault or nicked a cable the only difference is the fact that the new boiler has 3 new power supplies feeding the main circuit board, pump and fan.
Being high efficiency supplies they will leak a small current to earth due to the filtering capacitors.

Perhaps there is now enough leakage on the existing installation and the new boiler is just sufficient to trip the RCD.

Many properties still only have a single RCD feeding the whole installation and with countless high efficient power supplies (in each appliance) now connected it doesn't take much to hit the 30mA trip of the RCD.

As a boiler repairer I have generally advised the RCD is swapped out first (they can become more sensitive) and often this solves the problem.

Otherwise an electrician is required who can test earth leakage of individual appliances since one might have excessive leakage.

 

[CBW]

So if wiring is crap to start...and a boiler fitter dusturbs it causing earth leakage faults...It is all the fitters fault???? Yeah right.

Do you know wiring is crap? Nor do I, going off the little information that’s been provided.

 

[ericmark]

So if wiring is crap to start...and a boiler fitter dusturbs it causing earth leakage faults...It is all the fitters fault???? Yeah right.

In a way yes, it is the boiler fitters fault, if you install any new equipment you should test the supply first to see if it is OK, in the main I know we are lazy and stick in a socket tester only, but it can be debated with a FCU how much testing should be done. With a plug and socket we tend to take the attitude if they bought anything from a shop the supplier would not test socket, however we are installing a bit of fixed electrical equipment which the buyer can't simply return and say this is not good it trips my RCD.

I will admit I have a problem with RCD's as my clamp on will not measure 3.5 mA, so to measure that I would need to swap the FCU for a plug and socket and use my PAT tester, and I suppose that does raise the whole idea of using a FCU rather than plug and socket, although in an owner occupied home we may not need to inspect and test, in rented accommodation this is required.

We may call it PAT testing but correct name is "Inspecting and testing of in-service electrical equipment" so the boiler needs testing, there are two ways to test earth leakage, one is an insulation tester which uses 500 volt DC the other is a mA meter, but the latter needs inserting between the supply and appliance, so if you don't want 500 volt line to earth and neutral to earth then need to be able to unplug so a PAT tester can be used. And also of course the plug can be removed when the supply is tested.

Yes we all cut corners, but once there is a problem then that has to stop, and the appliance needs testing and the supply needs testing, if @Sajid.Y calls an electrician who tests the supply with a RCD meter with everything but the boiler plugged in and the RCD fails to trip on 15 mA and does it again with boiler plugged in or switched on and it does trip at 15 mA extra he could justifiably say boiler at fault.

This then leaves a problem, electrician says boiler and boiler fitter says supply, far better for the boiler fitter to find the fault and if he can show the installation resistance is under the 1MΩ he can then high light the fault for electrician to fix. Not testing just leaves the boiler fitter open to claims for electricians time.

It may well be there is a fault with the supply, but it would enhance customer relations if the boiler fitter actually said to customer you have a fault on your toaster or supply it is xΩ to earth and should be over 1MΩ and it means if a capacitor is faulty on the spike filter on the boiler which is the most likely cause, then he does not get a bill for the electricians time.

 

[Sajid.Y]

Many thanks for the many replies, to start with in note interested in suing anyone, but I'm definitely not interested in being out of pocket. There's been a number of smaller plumbing issues from their install that I sorted out myself.

In regards to the RCD testing, it was replaced with a new one and the problem persisted, the original electrician that came back did some testing but I do not know how sophisticated it was, he just managed to point to the wiring on the circuit where the boiler was connected to.

I've only been here for a year, so I'm not too sure with the electrical history of this house, but I have not had any issues for well over a year.

Also there was a survey done before the installation, and from what I have read above the boiler may have been connected onto an existing busy circuit.

Any which ways it sounds like I need to get an independent out here to find the cause, and if it is the installers then they'll get the bill along with anything it took to fix the plumbing.

 

[picasso]

Put your boiler on an extension cable plugged into a different circuit, if it still trips its the boiler if its ok it will be your house wiring.

 

[Sajid.Y]

Put your boiler on an extension cable plugged into a different circuit, if it still trips its the boiler if its ok it will be your house wiring.

Good idea will give this a try