immersion heater fault?

jaysparx · Oct 30, 2010

ive got home from work the past few evenings to find my rcd main switch has tripped, checked my sky tv to see what time it tripped, it was approx 9 am. This also happened today (saturday) same time, so i pushed cartridge fuses on DB back in one by one and found the fault to be on the immersion heater,
what i dont understand is why it trips at this time only, and not when it comes on in the early hours!
can anyone help please!

malcolmsanford · Oct 30, 2010

How long as the immersion been RCD protected ? What makes you think it is the immersion that is faulty ? The only way you can really prove the immersion is faulty is by doing a IR test on it.

Have you gas by any chance? Is there anything timed to come on at 9am CH perhaps?

The immersion could be breaking down, perhaps not fully as of yet and when it comes on in the early hours, with no other equipment on at that time it's not leaking enough to trip the RCD. At 9am other things may be then operating and that then would be enough to trip the RCD.

The tihngs to do is an IR test on the immersion if you think that is the problem, then a ramp test on the RCD to see what that is tripping at. Unfortuantely an intermitent fault is the hardest to find and you will need to have the right test equipment, knowledge and patience.

jaysparx · Oct 30, 2010

Its always been rcd protcted, the immersion is on its own fuse and its this one that trips the rcd, we have storage heaters not gas and they are one a seperate DB.
Also we're always out of the house by 9am so i dont think its extra load.
unfortunatly i dont have a multi-function tester at the moment, only a continuity! but i will look in to hiring or borrowing one!
Thanks again for your time and advice.

Octopus · Oct 30, 2010

What happens if you turn the immersion off and back on again at a "different" time? i.e. when you're in.

Guest123 · Oct 30, 2010

Can you alter the timer so it switches when you are present to see what happens???

Or,as you havn't the appropriate test gear, switch the immersion off at it's DP switch one morning before you go out and see if the RCD has tripped when you return. If not then you know the circuit is fine and the element is to blame.

jaysparx · Oct 30, 2010

i switched off dp switch on timer, popped fuse back in on the DB then switched timer on again, and it holds! so i have hot water now but i just dont understand why it always trips when it comes on in the morning! i will see what happens in the morning, im fairly new to the trade (2 years) so i might have to swallow my pride an get a proper sparks in! LOL
I'll keep you posted, thanks for the replys.

malcolmsanford · Oct 31, 2010

jaysparx said:
i switched off dp switch on timer, popped fuse back in on the DB then switched timer on again, and it holds! so i have hot water now but i just dont understand why it always trips when it comes on in the morning! i will see what happens in the morning, im fairly new to the trade (2 years) so i might have to swallow my pride an get a proper sparks in! LOL
I'll keep you posted, thanks for the replys.

If your in the trade Jay then you should be able to get hold of a Insulation Resistance tester, or to be honest you should have one. This is the only way to test that element and is a great tool to have for any fault finding.

If the element is holding in then chances are it's not that. Next thing to look at is that timer. Try leaving the timer out of the equation for a couple of days, just working the immersion/CH on the thermostat. If it dosen't trip then it may be that

telectrix · Oct 31, 2010

IMHO , IR test is the only way to find this fault. otherwise it's head scratching trial and error for the forseeable

andyb · Nov 1, 2010

How can it be head scratching trial & error?
An immersion circuit is one of the simplest circuits in the house, it's a simple radial.
Switch off the immersion & test the element, I think you'll find that that is where the problem is. It's always the element. Drain the tank & change the element.
If the element is ok test the circuit up to the time switch.

But I think you'll find it's the element, if you are using an immersion as your only means of heating water then it will only last a few years.

jaysparx · Nov 1, 2010

cheers malcom, my firm always gets someone in to do the testing so ive not had much call for one, but i can prob convince the missus that i need one now!
thanks again.

ian · Nov 1, 2010

I have seen this problem before, and I found the element was contracting when it cooled down and tripping the RCD. I could not get a fault when I tested because when I arrived it had sealed itself again. When I changed the element it was magically sorted. The problem is relatively common when the element it heating up and expanding, not quite as common when contracting.

Ian

Jabbajaws · Nov 1, 2010

Could l ask guyz, about the actual IR test itself on the immersion heater.?

Im a little bit confused about the test, with it being done on an immersion heater (Sadly l do not have test equipment at present).

If an IR test is done on the element itself, what will be the expected approximate reading if it is in working order? (Im assuming a high IR reading would indicate that the element is damaged in some way).

And why would an IR test be required and not a continuity test on an element? Isn't the element a bare conductor? And wouldn't that affect the IR reading, with the element not having insulation?

telectrix · Nov 1, 2010

sorry you are way out there. IR test should read high. rem. IR test is to earth! the higher the better. continuity should read around 18-20 ohms. the element is not bare, it's mineral insulated in metal.

keniff · Nov 1, 2010

I test by ir, l-n should just be dead short, for example 0 meg ohms on my megger, if I get a reading it's starting to deteriorate

Jabbajaws · Nov 2, 2010

Thank you for the feedback. One final concern l have regarding electrical immersion heaters.

Does anyone remember a few years ago, a fault occuring on a domestic immersion heater, in England, after which the thermostat failed, and the immersion continued to boil constantly, until it eventually exploded, with the tragic loss of a young infant, who was asleep on the floor below.

I noticed that on the news, it was announced that a simple part could have been fitted to the immersion heater to prevent this for a mere cost of approx £5.

What id like to know is What is the part that can be fitted, to prevent this from happening again? Does anybody know? Any info much appreciated...