Immersion tripping MCB - a few questions

DonalB

Hey all,

My immersion recently started tripping an MCB switch (as far as I know the immersion is almost 20 years old), previously switched on for about an hour every morning, controlled by a electronic timer attached to the switch.

Are there any simple diagnostic tasks to establish the cause I could carry out before I'd have to call an electrician? I'm strapped and looking to minimise costs. I have a multimeter, I'd be comfortable doing simple wiring by following plans but I realise that no-one is likely to suggest much. I wired the timer into the switch myself following instructions in the retail packet about six years ago.

The power trips immediately when the timer clicks on. It trips the MCB for the circuit box rather than the specific Immersion breaker.

I would call an electrician but as I said...

Finally, and a further dumb question, what's the most likely cause and possible cost of it (min/max)?

Thanks for any answers or advice.

mikehammer67

RCD-the one that knocks off all the sockets

immersion most likely needs replacing anyhow

you can prob test the heater to earth with your multimeter,and do a visual check of wiring for faults

Bruthal

Very likely the element needs replacing alright.

North West

Hi Donal
Get your voltage test meter. connect to Neutral pole and live pole on immersion. If you get a reading the element is gone, you will need to replace complete immersion.

Now if you get no reading connect to neutral pole and live coming from main to thermostat and if you get a reading the thermostat is gone.
NW

mikehammer67

North West wrote: »

Hi Donal
Get your voltage test meter. connect to Neutral pole and live pole on immersion. If you get a reading the element is gone, you will need to replace complete immersion.

Now if you get no reading connect to neutral pole and live coming from main to thermostat and if you get a reading the thermostat is gone.
NW

no

he has an rcd trip and it's tripping instantly

Philip82

One way to check the elements in an imersion or any element for that matter without having power on is by simply testing for continuity between each leg of the element. Eg. Disconnect the cables from the element and try for continuity between each leg. If your element is gone it wont ring out and if its not it should, after all its just a coil of heating metal strip that heats up inside the outer casing. You can also test for continuity between thermostat input output which should always ring out when power is off. Hope this helps.

Bruthal

Philip82 wrote: »

One way to check the elements in an imersion or any element for that matter without having power on is by simply testing for continuity between each leg of the element. Eg. Disconnect the cables from the element and try for continuity between each leg. If your element is gone it wont ring out and if its not it should, after all its just a coil of heating metal strip that heats up inside the outer casing. You can also test for continuity between thermostat input output which should always ring out when power is off. Hope this helps.

If you want to test continuity of element, a good way is a multimeter set on lowest ohms setting is the way.

About 26 ohms for sink, 17 ohms or so for bath.

Bruthal

North West wrote: »

Hi Donal
Get your voltage test meter. connect to Neutral pole and live pole on immersion. If you get a reading the element is gone, you will need to replace complete immersion.

Interesting, but I am at a loss as to how that works....

With a functioning element, there will be 230v on the ends of the working element. If the element is gone, but power has not tripped due to the element fault, there will still be 230v on the element ends.

Now if you get no reading connect to neutral pole and live coming from main to thermostat and if you get a reading the thermostat is gone.
NW

Again, how?

Immersions with single stats have the main neutral into the stat.

If you want to test the stat, connecting the voltmeter probes to each side of the stat will show 230v if the stat is open, and 0v if it is closed, with a properly functioning element. This test only really checks the stat when the water is cold in the cylinder, and the element is known to be good.

The OPs problem is a tripping RCD by the sounds of it, likely from an earth fault in the element. A multimeter testing the disconnected element ends to earth might show this. Better still is a meggar.

.G.

Must immersion fault season at this time of year,a lot of problems lately!

Cerco

We are using the immersion more since the central heating is off at this time of year. So issues more likely to arise.

reach for the stars

Just turn off main rcd ,disconnect immersion wires at switch and repower circuit if still trips immersion gone ,get new immersion, tie up ballcock in attic ,run hot water to drain water from tank,get immersion key and replace immersion (be carefull not to warp tank flange when opening closing can sometimes be a bstrd to get a seal) rewire and away you go

Cerco

reach for the stars wrote: »

Just turn off main rcd ,disconnect immersion wires at switch and repower circuit if still trips immersion gone ,get new immersion, tie up ballcock in attic ,run hot water to drain water from tank,get immersion key and replace immersion (be carefull not to warp tank flange when opening closing can sometimes be a bstrd to get a seal) rewire and away you go

Maybe I misunderstand your suggestion but if the element is disconnected and the mcb/rcd still trips, that would suggest something else, other than the element, is faulty.

mikehammer67

hmm i don't really understand that suggestion either


i don't see how you've learnt anything new by disconnecting wires and switching on .........?

it's basically the same thing as turning off the DP switch


the OP already can be reasonably sure the heater needs replacing-to be certain you can test heater..........

reach for the stars

Cerco wrote: »

Maybe I misunderstand your suggestion but if the element is disconnected and the mcb/rcd still trips, that would suggest something else, other than the element, is faulty.

Well then you dont understand but like the other clown after you ,you still will comment ,i am trying to help this guy out if you dont understand and have nothing constructive or helpful to add to the conversation then fk off and mind your own business

Cerco

"Well then you dont understand"........ SNAP!

No need to get irritated because you cannot explain your suggestion. Bad advice is worse than no advice.

JOHNPT

What does a 50 ohms resistance between the bath & sink element indicate?

brightspark

JOHNPT wrote: »

What does a 50 ohms resistance between the bath & sink element indicate?

What is the resistance of each element?

_______SINK_______
!
!
!_______BATH ______


Don't know the figures for each, but I think if you add them you get 50?

brightspark

reach for the stars wrote: »

Just turn off main rcd ,disconnect immersion wires at switch and repower circuit if still trips immersion gone ,get new immersion, tie up ballcock in attic ,run hot water to drain water from tank,get immersion key and replace immersion (be carefull not to warp tank flange when opening closing can sometimes be a bstrd to get a seal) rewire and away you go

Surely you meant that if the circuit doesn't trip, then it's the immersion?

Bruthal

brightspark wrote: »

What is the resistance of each element?

_______SINK_______
!
!
!_______BATH ______


Don't know the figures for each, but I think if you add them you get 50?

Around 17 ohms for bath, 26 for sink.

Bruthal

reach for the stars wrote: »

Well then you dont understand but like the other clown after you ,you still will comment ,i am trying to help this guy out if you dont understand and have nothing constructive or helpful to add to the conversation then fk off and mind your own business

Well, telling "this guy" that removing the element from the circuit, and the circuit still tripping proves its the element, is hardly helpful.

brightspark

Bruthal wrote: »

Around 17 ohms for bath, 26 for sink.

17+26=43, close but not 50.

@JOHNPT is this a real immersion, or a theory question?

If a real immersion is the immersion by any chance rated at 240V, then the values would be in the region of 19 + 29 = 48 Ohms?

Other possibilities are..

meter accuracy including probe contact resistance on corroded terminals.

poor connection from the terminals to the elements including the connection between the elements, if this is the case i might expect to see some heat damage at the connection.

I'm sure I may have forgotten something but it's been a long day.

mikehammer67

Bruthal wrote: »

Well, telling "this guy" that removing the element from the circuit, and the circuit still tripping proves its the element, is hardly helpful.

what does it prove ?

disconnecting the wires and switching on?

nothing that you don't already know unless i'm missing something obvious?

Bruthal

mikehammer67 wrote: »

what does it prove ?

disconnecting the wires and switching on?

nothing that you don't already know unless i'm missing something obvious?

It certainly doesnt prove its the element group. Thats what Im saying.

As in the poster is calling people clowns, while wrongly posting a test method.

Bruthal

brightspark wrote: »

17+26=43, close but not 50.

Close enough for the needs here. Some bath elements are 2.7kw or so.

That would be near 20 ohms and 27 ohms, totalling 46 or 47 ohms. I doubt elements are absolutely spot on in rating. And neither are all ohm meters.

If getting 50 ohms for both elements in series, then in my opinion its close enough to 50 to suggest the element is reading a correct reading. Its not a guarantee there is not an earth fault though.