RCD tripping from immersion heaters

[CrazeUK]

Hi all.

My flat runs on Economy 7. So is fully electric. It has a hot water tank with 2 3kw immersion heaters on a Hertsman e7 controlller.

I recently had an issue with an 8.5kw shower solenoid. I took the opportunity to upgrade to a 10.5, so swapped the cable for 10mm Twin and Earth.

Everything has been working fine.

Last night I couldn't sleep, so decided to have a shower at 4am, whilst the immersion heater was running and the tank was heating. As normal I heard it hissing (kettling) just before I turned the shower on. I hit the shower button and the electricity tripped.

I noticed the RCD had tripped, so went down the usual of turning MCB's off to find the culprit. It was the immersion heaters. The hortsman stayed on.

Today I tried to hit the boost on the horstmann, and nothing (electricity usage didnt go up) and it didnt tripped (I think only one element comes on at night.

Do I just do a continuity test on the element cable?
Is it something I can change my self?

 

[EFLImpudence]

Strictly speaking 10.5kW is too much for a 40A MCB.

 

[CrazeUK]

I thought so, I spoke to an electrician who said it should be fine. He said if it trips while in use, then swap it for 45A.

Strictly speaking 10.5kW is too much for a 40A MCB.

 

[EFLImpudence]

I'm a bit confused but -

Last night I couldn't sleep, so decided to have a shower at 4am, whilst the immersion heater was running and the tank was heating. As normal I heard it hissing (kettling) just before I turned the shower on. I hit the shower button and the electricity tripped.

Ok.

I noticed the RCD had tripped, so went down the usual of turning MCB's off to find the culprit. It was the immersion heaters. The hortsman stayed on.

How could the Horstmann stay on if the RCD had tripped?

Today I tried to hit the boost on the horstmann, and nothing (electricity usage didnt go up) and it didnt tripped

Does that not suggest a fault caused the trip and something has stopped working?

(I think only one element comes on at night.

Yes, the main/bottom one if that is what the timer is set for - but the boost works the top element.

Do I just do a continuity test on the element cable?

Maybe, if that is where the fault is.
Probably better to check the disconnected element first. L - N, L - E & N - E

Is it something I can change my self?

Is what something you can change yourself? Element - probably not.

 

[CrazeUK]

I'm a bit confused but -


Ok.


How could the Horstmann stay on if the RCD had tripped?


Does that not suggest a fault caused the trip and something has stopped working?


Yes, the main/bottom one if that is what the timer is set for - but the boost works the top element.


Maybe, if that is where the fault is.
Probably better to check the disconnected element first. L - N, L - E & N - E


Is what something you can change yourself? Element - probably not.

Many thanks for the response.

I assume the Hortsmann has a back up battery that keeps it going. I have just tested it, when i turn the MCB off, it still stays on.

In my "uneducated" knowledge, turning the electric shower on, combined with the 3KW immersion heater, surged in some way, tripping the element. - If the element is damaged.

I will do as youve suggested, i have a multimeter, so should be straitforward.

Once i have tested it through, i will call a electrician out (or is this a plumbers job lol).

 

[CountryFan]

Once i have tested it through, i will call a electrician out (or is this a plumbers job lol).

I would call an electrician as not all plumbers know about electrics. Also, the photo of the consumer unit, the MCB that's down, down flow heater - are you saying the immersion is connected or is that not in use?

 

[EFLImpudence]

I assume the Hortsmann has a back up battery that keeps it going. I have just tested it, when i turn the MCB off, it still stays on.

Ah, ok, maybe for the clock but it wouldn't switch on the element.

In my "uneducated" knowledge, turning the electric shower on, combined with the 3KW immersion heater, surged in some way, tripping the element. - If the element is damaged.

Well - sort of - possibly but not as you are probably thinking.
A fault somewhere else could trip the RCD when 57A turned on.

I will do as youve suggested, i have a multimeter, so should be straitforward.

Mmmm.

Once i have tested it through, i will call a electrician out (or is this a plumbers job lol).

Well, one who can do both.

 

[CrazeUK]

I would call an electrician as not allowed plumbers know about electrics. Also, the photo of the consumer unit, the MCB that's down, down flow heater - are you saying th immersion is connected or is that not in use?

Cool thanks.

That MCB that is down, is a kitchen wall mounted downflow heater i removed. The wiring is still there, and capped. So left that MCB down.

I just realised, I amdidnt attach the annotated pic of the CU.
1. Is the MCB for the Immersion heater - that doesn't trip when the problem occurs.
2. The RCD that trips when the immersion is on.

 

[ericmark]

An RCD checks for imbalance, so there could be a neutral - earth problem which has only showed up with the increased load. I would start by turning all off, then starting with RCD turn them back on, one more at a time and see if anything trips.

 

[Harry Bloomfield]

Is it something I can change my self?

It seems likely, that it is the immersion heater element, which is failing, the longer one, used during the night, on E7. Assuming it is an open-vented hot water system (large header tank in the loft), fitting a replacement can be a DIY job. You will need an immersion heater socket spanner, to get the element out, and fit the new one.

The first job, will be to isolate the power, then either isolate the water supply to the header tank, or tie up the ball valve, so no more water goes in, then turn all of your hot taps on to drain the water down as much as possible, before beginning to try to remove the element. There will still be a few pints of water escape, even then, so plenty of old towels ready to catch it, always assuming the elements are cylinder top mounted.

The element will probably be a 27" one, best to get a new, matching thermostat to go with it.

You need to be firm, but also gentle in trying to undo the element - undo a fraction, tighten a fraction, until it turns out easily. Make sure you get/install a new gasket.

 

[ericmark]

drain the water down as much as possible

Plumbers tell me not to do this, it is more likely to damage the tank, removing it empty, so I employed a plumber to change mine.

 

[Harry Bloomfield]

Plumbers tell me not to do this, it is more likely to damage the tank, removing it empty, so I employed a plumber to change mine.

You cannot empty the cylinder - You can only drain the header tank down, and pipework, to the highest point of the cylinder. Which in fact, is the top of the pipe, which comes out of the cylinder top/centre. Which was why I suggested lots of towels..

 

[pete01]

Make sure you crack the element (loosen) with the tank full of water.

 

[pete01]

Have a little grow up mate, if ya like.... this blokes good and pretty comical.

 

[EFLImpudence]

Has anyone said where the element is?

Top entry - as with 27in. - or side entry near the bottom.