Boiler tripping RCD

Mr.Stu

Mr.Stu

Mr.Stu

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18 Oct 2002
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Any ideas chaps?

- 30-60 minutes after the boiler kicks in the RCD trips and we lose all plugs in the house
- Turning the boiler off at the wall then allows us to reset the RCD and everything is dandy again
- Happens when boiler is on for either heating or water
- Has been happening for about 10 days
- Tried removing every other electric device in the house, turned sockets off, test > still happens
- Two boiler engineers have visited and looked at the boiler (Myson) and said, it's too old to diagnose, buy a new boiler. One said it might be the fan.
- An electrician has been out an checked all the wiring rings in the kitchen and up to the boiler and they appear OK
- No on has actually checked the electrics inside the boiler, it seems like a grey area that no one understands

Google-fu suggests all manner of things, and stories of people replacing every component in the boiler and still having the issue.
 
Well how old is the boiler, old enough for the skills required to fix it to be lost and no parts available? could try BG one off repair service? no fix no fee? request the oldest gas engineer available?

The fault could be on the boiler itself or on the control wiring, this wiring goes to the room stat, controls the zone valves etc, fault on this should be easy to fix, an electrician familiar with heating wiring should be able to test this and diagnose any faults.

Have you tried playing with the controls to try and get it to trip? so switch on heating only, then hot water only, then both to move the valves and use all the wiring and see if for example a particular setting causes the trip.

You would think old boilers have almost no electrics inside them just pretty much on or off, no pcb, self test of anything complicated to go wrong.

Good luck getting it sorted, at least it didn't happen over winter
 
ps.

30-60 mins sounds like maybe its happening as the stat is switching the boiler off because its reached the required temp? could turning temp down the see if the trip happens when the boiler turns off?

Try heating only, and turn room stat down after 5 mins, see if its trips? and try hot water only and turn stat on tank down after 5 mins?

Did the electricians testing show an IR fault or not? or he didn't test with the boiler spur switched on? also IR faults can be intermittent and only show up and cause a trip then disappear again. can be hard to track down.

Also loose connections can trip rcd's. might be worth checking all connections if there is no IR fault showing up during testing, could be any loose connection on that circuit but most likely after the boiler spur.
 
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Thanks for the comments.

We (me + several boiler engineers) have tried every combination of heater/water and thermostat adjustment. It does not seem to be linked to the system reaching required temp. However it does seem to only happen the when the boiler is actually on (visible flame).

No engineer has seemingly had the skills so far to diagnose electric faults specific to the heating system, perhaps I need to keep looking for the right person.

Boiler is about 16 years old, serviced regularly.
 
such an easy fault to find..

their are only a few things on a combi capable of tripping an RCD..

i guess just keep trying with engineers..

sorry i cant tell you what to look for, unless you have a gas safe number..
 
Hi, it's got a separate tank upstairs for the water.

Afraid I'm not competent enough with electronics, but hopefully I can find someone who is - sounds like I should keep pushing rather than replace the entire boiler!

Thanks
 
I think so (sorry, I'm not familiar with the terms used).

I have a boiler in the kitchen, which fires up when GCH or DHW is used.

In the cupboard upstairs I have a tank with thermostat on, a pump and diverter valve.

Cheers
 
Did your electrician check all the wiring for the heating system or just upto the spur (switch) that powers the system?
 
RCD trips on earth faults, when either the live or neutral shorts to earth, seen a RCD trip out in the past with a boiler, one with a faulty motorised diverter valve, several others with a faulty pump.

When they kick in, seconds later the rcd trips out.
 
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Is there a leak causing something else to short and trip it? Turn on boiler, water leaks somewhere, builds up after about an hour and shorts something.
 
Unlikely to be your boiler tbh. Could be a number of faulty parts on the system. It could be the cylinder is getting up to temp and the cylinder stat is switching over causing a earth fault somewhere. Like the valve moving over or the pump being faulty etc. What you need is an electrician with an idea of heating systems, So ask before you call one out. A heating engineer is likely to just change parts out, it needs to be tracked by an electrician. Hope that helps. :)
 
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