# Intermittent RCD tripping



## MattP1 (Apr 14, 2021)

My Andreja has in the last 2 days tripped the RCD on the fuse box twice.

Neither was at switch on.

First time was after around 10 minutes but I put this down to possibly moisture inside as it had got some water around it during transit and I may have missed some.

Today it was fine this morning, on for around 30 minutes before I realised I had an issue with the microswitch so powered off to cool, fixed switch and powered up again, made coffee. Powered off.

Mid afternoon, powered up again and it tripped the RCD after around 10-15 minutes I think. I reset it and turned on again, was fine for another 20 minutes until I turned it off.

I did this morning put an inline RCD socket, this I'm sure is the same rating as the fuse box (30mA) but it tripped at the fuse box still not the local RCD.

Can anyone suggest where to start looking to investigate this? Thanks.

I've read about measuring the heating element but I don't think it will give anything obvious as mostly working as it should. I could leave it powered on with the element disconnected?

Not sure if it's relevant but it's an old house with old wiring but I haven't had issues with anything else. Google results suggest it isn't uncommon.


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## DavecUK (Aug 6, 2013)

It was very common on those for the limit stat to corrode/burn out and cause the RCD to trip. If you take a photo of the top of the boiler, I will indicate for you, the limit stat.


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## El carajillo (Mar 16, 2013)

Several variables there, how did it get wet in transit ? how wet ? Old house , wiring ? faulty burned socket, loose connections , faulty / worn lead,

Loose wire in plug, loose fuse, broken strands. Anything else on the socket / circuit ?

How old is the machine , has it been serviced ? Possible fault /arcing on the pressure stat


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## MattP1 (Apr 14, 2021)

Had the case off again this morning. Happy with house electrics side. Running on same socket used for 2kw heater and dehumidifier (one at a time!). Retightened or reseated all power connections.

Two issues identified.

1. Slight leak from the screw holding the level sensor magnet in the tank. Previous owner had it plumbed. Tightened but may add some silicone too.

2. I believe this is an anti vacuum valve but see video. It seals at high pressure and weeps at lower pressure? When powered on from cold it sprays a lot of water whilst spinning. Not really visible in the video as I let the pressure drop but it heated back up too quickly. This ties in with a trip 10 minutes after power on from cold.

I'm cooling it now to get a better video.


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## MattP1 (Apr 14, 2021)

Removed video. See below on YouTube.


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## DavecUK (Aug 6, 2013)

@MattP1 Just upload your videos to you tube as unlisted, then link to them here, we can get full res vids no problem that way. I can't see the videos at all, just a large grey box. Don't forget that photo of the top of the boiler.


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## DavecUK (Aug 6, 2013)

I managed to download the vids by opening your post in edit mode and uploaded them to YT as unlisted


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## MattP1 (Apr 14, 2021)

Thanks. I have removed the videos from the post now.

I didn't capture the valve spitting first time but you can see how much water has been sent across the boiler and is boiling off.

The valve spinning video was afterwards when I released a lot of steam but the spitting was much reduced as it was up to temperature.

Photo of top added. Is the level sensor on the right of the limit stat?


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## DavecUK (Aug 6, 2013)

As I suspected, the vacuum breaker cup is leaking badly over the top of the boiler, they always did eventual;ly. This is tripping the limit stat, which will be badly corroded anyway.

You need to replace the vacuum breaker, limit stat and clean up the top of the boiler. Careful with the connectors, the plastic covers will be quite brittle by now. Use any limit stat with the same fitting that is ideally 140C or greater+ (145 would be an ideal value). Check the safety valve as well.

Check the rest of the machine for leaks...looks like the seller must have known there were a few problems, but you should be able to easily fix it up again.


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## DavecUK (Aug 6, 2013)

Limit Stat


Vacuum breaker


Safety Valve


Level Probe


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## MattP1 (Apr 14, 2021)

Thanks. Here is a better video of the extent of the spitting once cooled for a while.


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## DavecUK (Aug 6, 2013)

@MattP1 Yeah, theres a lot of water...when you change the vacuum breaker, dip the boiler to get a good idea of water level....draw water from a hot boiler first in tiny increments, until it autofills....then let it cool before dipping.

DONT touch or mess around with the level probe....if you need a new one, you will have to cut it to the same length as the existing one!!!


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## MattP1 (Apr 14, 2021)

Parts ordered but the vacuum valve isn't coming out easily. The basket has corroded and come away leaving the remains under the valve which won't be helping.


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## DavecUK (Aug 6, 2013)

@MattP1 yeah, you either need an impact wrench (air or electric, with good sockets)....or place a well fitting open-ended spanner on the fitting at the base and then tappy tappy on the other end with sharp raps to shock it loose...heafty bangy bangy, will snap the fitting off or damage the boiler....accompanied by curses and tears.

The manufacturers thread lock them in with superman super duper threadlocker, on the assumption that you will never need to change a consumable item that lasts 3-5 years. As you can imagine, this annoys the hell out of me;


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## Nightrider_1uk (Apr 26, 2020)

DavecUK said:


> ...looks like the seller must have known there were a few problems, but you should be able to easily fix it up again.


 Probably why he sold it


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## MattP1 (Apr 14, 2021)

Just to update, parts arrived last week but had to go away with work.

Replaced the limit stat, plastic covers on spades did crumble off so currently bare, plan to heat shrink.

Never got the vacuum valve off, it will need an impact gun which I will see if I can borrow off someone. Using leverage just moved the whole boiler.

It's running fine this week but still needs to be finished at some point.


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## DavecUK (Aug 6, 2013)

MattP1 said:


> Just to update, parts arrived last week but had to go away with work.
> 
> Replaced the limit stat, plastic covers on spades did crumble off so currently bare, plan to heat shrink.
> 
> ...


 Well done, just one small job to do...hopefully you cleaned it up inside at the same time (helps spot new leaks)....We need photos of the fix up, or it didn't happen. 😉


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