HELP !!! RCD Mystery

[Njay]

My son and his wife moved into a house about 7 months ago, they have had a new consumer unit and a new combi boiler fitted about 5 months ago and everything has been fine up until now. My daughter in-law phoned the other morning to say that the electric had gone off in the house and everytime she attempted to reset the rcd it would just trip straight off again…I told her to switch off all the mcb’s and then reset the rcd from there she turned every mcb back on one by one until the rcd tripped again and it was on the ring main that it tripped so I told her that there was something usually kettle or washing machine that is causing the rcd to trip…the last thing she unplugged was the combi boiler and then the tripping stopped and also the electric stopped on once the combi boiler was plugged back in. Later that morning I went round to pick our grand daughter up whilst I was there I just tried a few things but as soon as I turned the kettle on the rcd tripped…I said I’m pretty sure it’sthe kettle. Later that day she bought a new kettle, when I spoke with my son the next day he said it tripped again when she was hoovering and also when they used the new kettle one time???

The combi boiler sits in a utility room with the washing machine which are both plugged into a double socket. The following day I went round with my insulation resistance tester to check earth leakage on the boiler and kettle even though the kettle is brand new, but all was ok apart from the washing machine which was just over3MΩ. What I did next was to plug a rcd adapter into the plug socket then plug the boiler into the rcd adapter turned the power on and everything was ok then I turned on the kettle and then the hoover after about 30 seconds the rcd tripped on the mainboard as well as the rcd adaptor that the boiler was plugged through???It looks like a fault on the boiler…but I don’t understand… if there is a fault on the boiler why it isn’t tripping constantly and only tripping the rcd when other appliances are being used? I would be so grateful if anyone could help meunderstand what might be happening here, but be gentle it is my first post!!!
Also are thereany regs that state whether the boiler should go through a switched fused spur instead of being plugged directly into a double socket?
Thanks in advance for any help and advice given.

 

[Engineer54]

As the the CU and combi have only been installed for 5 months, get the companies back that installed them... It could well be a faulty RCD or multiples of natural/normal leakage from appliances on that circuit, or across the other circuits that the RCD is also protecting, or the internal electrical components of the combi boiler!!

BTW, what's wrong with a IR of just over 3 Meg for the washing machine, ...that's over 3,000,000 ohms??

Anyway, that would be my first step ....

 

[guest119]

Faulty pump?
Test it on its own?

Boydy

 

[Darkwood]

Sounds like a loose connection in the consumer unit...possibly a N or even a crushed wires against each other which may mean an unrelated circuit can trip the RCD .. these can be tricky faults to find but if load dependent and really needs a competent experienced Electrician with knowledge of this fault otherwise you pay for scratching of heads do light loads not trip and heavy trip?..

Why are you IR testing appliances you are likely to damage them... washing machines have smoothing capacitors and electronic control boards not something you should be IR testing even at 230v as the results will be misleading.. also drop all points forward on the ring and look for a loose connection as arcing can trip RCD's

You state your a domestic appliance Engineer ... ? Not sure if this title exists in real terms as an engineer has to complete a course like HNO Or HNC to gain that title, don't tag yourself with a sales pitch title on the forum as we see through that stuff, if you had Engineer qualifications this question would not of been asked IMHO and Ive never heard it tagged to domestic appliances before with diploma or similar recognition?

Lastly welcome to the forum:smilewinkgrin:

 

[Njay]

First off all thanks for all your replies and suggestions, I'm sorry if I hit on a sensitive nerve darkwood by stating I am a domestic appliance engineer, it was just a question that cropped up when joining the forum about my job title... and that is what the company I work for call the position I hold....will see if I can rectify that in account settings maybe domestic appliance repair man will sit more comfortably with you ?https://www.electriciansforums.co.uk/images/smilies/smilewinkgrin.gif But I can assure you 100% I'm not after work or trying to sell anything just curious what could cause this problem? But back to the problem yes your right it does only seem to trip on heavy loads especially when the kettle is used...but not every time? The reason I carried out the insulation resistance test on the appliances was because I wanted to try to eliminate them out of the equation if possible and as part of my job I have access to a Portable appliance tester.I think its looking as though my son is going to have to get either the boiler people out or the electricians who fitted the consumer unit...not sure in what order though ??? In the past when similar problems have occurred in my house or friends or family its usually strait forward like a kettle gone to earth or washing machine...but I've never came across anything like this and I'm just intrigued by what could cause this type of problem??? somewhere else in the forum I read a piece about accumulative earth leakage from several appliances? could that even be it ??? Once again thanks for your help and suggestions.

 

[Knobhead]

Do they not have a warranty for the work done?

Tell them to stop messing about and get the people back.

 

[Octopus]

I'd be looking for a N-E fault on all the circuits on the same RCD, so don't assume its the boiler or the socket circuit!

 

[UNG]

Odd faults like that I always check the fridge / freezer if it has an auto defrost it quite often kicks in at random times

 

[pjcomp]

I think the odds are in favour of the boiler being the problem - you say it doesn't always trip with the boiler plugged in, but was the boiler actually operating? If the boiler had switched itself off internally because there was no call for heat/hot water, then there wouldn't be any reason for it to trip; boiler cuts in shortly afterwards - ping, off you go.

PJ