CH blowing RCD after being flushed.

[Colin Chaplin]

Evening All

On our consumer unit in our 7 year old house, the "circuits protected by RCD connection" started tripping this morning (apologies for the bad explanation, her indoors is telling me down a phone line)

It's not the individual "fuses". I'm thinking this indicates an earth leak, because as soon as it's pushed up, it trips. All sockets go off but lights remain on.

Our central heating is fairly common I guess; gas burner thing in the kitchen and hot water tank with immersion upstairs. With a bit of deduction, I figure out it was this and got her to turn it off (it has a wall switch). The power remained on. Turning it on trips the power so kinda proves there's a problem there.

NOW

On Thursday/Friday last week I drained the radiators, injected the cleaning stuff then the presevative as instructed. All good, Rads hot and smug feeling of satisfaction. Her indoors did moan they were making funny noises so it might need more bleeding. But ignoring the problem above, all OK. I THINK. . The two events are too close together to be coincidence. I've told her to take a shower and wear a jumper till I get home.

Does anyone have any idea of anything obvious to check, so I can stun her with my technical brillance?

Cheers

Colin

[Lobster]

A slow/slight leak somewhere (eg drain c*ck, bleed valve) which has let water get into an electrical connection and is shorting it out?

David

[Roger Mills]

Indeed - look very closely at all points where electrics come into close proximity with potentially wet bits.

Ignoring the fact that you've just flushed it, by far the most common cause of trips is earth leakage in the pump. It's worth checking, and *could* be a co-incidence and nothing to do with your flushing work. The easiest way to check this is to disconnect the pump wiring, and wire it into a 13A plug instead. If the electrics immediately trip with *just* the pump switched on, you have found your culprit. [If you want to check whether the heating system *still* causes a trip with the pump disconnected, don't run the boiler for more than a few seconds - otherwise it will overheat with no circulation].

[meow2222]

Unfortunately it doesnt, but yes its the most likely culprit. You need to get your multimeter out and track the problem down.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Colin Chaplin" saying something like:

Hmmm... It might be. Otoh, the pump might be stalled from loosened crap and developed an electrical leakage. As far as the boiler controls go, offhand I'd say there's nothing you did that could have affected them electrically.

One thing to check; if your CH supply is piggybacked off the immersion circuit, make sure it's not the immersion at fault. It's not unknown for that to happen and for the immersion to be RCD fed.

[John Rumm]

Or turn the gas off at its service valve...

[Roger Mills]

Maybe. But that could cause problems if the boiler goes through the motions of trying to light, but can't because of lack of gas - and eventually goes into lockout mode.

He could just turn the boiler stat down to zero - although I suppose that would stop it trying to do anything - so that if there *is* an electrical fault in the boiler, it may not show up.

I still think that the best bet is to allow the boiler to fire, as long as it's only for a few seconds.

From what the OP said, the trip went as soon as the CH started up - so if (with the pump disconnected) the boiler can fire, even for a very short while, without tripping the electrics, it sort of eliminates it.

[Colin Chaplin]

All Good stuff, Cheers fellas. I will be home late tonight so go at it tommorrow. Keep your fingers crossed, and I will report back!

[John Stumbles]

- called a boiler

- more usually called a cylinder because it is, er, cylindrical

- 'it' being the immersion you just mentioned?

So if the electric immersion heater in the hot water cylinder is switched on the RCD trips, if it's off there's no problem. Then, as long as nothing else is conected off that circuit, it looks like your immersion heater is faulty.

...

What law of nature dictates that? Whilst I share your suspicions and it can be a useful guide, it can lead you in the wrong direction. In this case logical analysis points to a different conclusion.

[Colin Chaplin]

"John >> The two events are too close together to be coincidence.

Logical analysis points to a different conclusion, but it was wrong!

i got home last night, and on closer inspecion, the expansion tank at the top had been leaking, and dribbing down the electrics inside. I removed the front panel and the connectors were all wet.

Left the panel off overnight and appeared dry this morning. Gave it half an hour with a fan heater just purchased and evertyhing looked sound.

Turned on, hope for the best. Which is, what I appear to have. I am sitting here and the house is getting toastie. No evidence of water continuing to leak but I will need to keep an eye on that as theres no reason for it to magically fix itself.

So, Kudos to Lobster who predicted it correctly!