Immersion heater tripping probs!!

[diverdan74]

Hi all, thanks for the replies, will get a photo uploaded today.
The whole heater was changed 2 months ago as the old one had been in since the year dot and had simply given up.
A plumber went round and changed it (new element and stat) in since tripped the MCB. This is where i went round to have a look. Found it was on a 32amp Ring main so put in a 16amp MCB new 20amp double pole switch. Only have a multimeter but done continuity and resistance tests on the wiring and that was sound. Switched it on around 12pm, 30mins later warm water, 2 hours later it tripped the MCB. So new stat, still trips after a hour or so!

Was just going to bypass the stat to see if the MCB trips straight away, not as a long term thing.

The Backer stat that i put in will only switch off if i physically push the adjuster down i can not hear any click when adjusting from min to max is that right?

Thanks again, Dan

 

[martinxxxxxx]

(Ideally this should be done at 500v with an insulation resistance tester, and readings of 10s of megohms at least would be expected).

This HAS to be done with a insulation resistance tester. Your multimeter won't tell you that the element is breaking down.

Have you disconnected the element and tested the resistance between the element terminals and the earth body of the element.

as flameport says:
(Ideally this should be done at 500v with an insulation resistance tester, and readings of 10s of megohms at least would be expected).

I would argue that

This HAS to be done with an insulation resistance tester as your multimeter won't tell you that the element is breaking down, unless it is already a short to earth.

 

[Darren1234]

Just thinking about somethign else, is it definitely an MCB you've put it on and not an RCD?
(An RCD will have a 'push to test' button)

Your problem just doesn't seem to add up. If it can heat for two hours and then trip I wouldn't think there is any break down in insulation . By the sounds of it, the thermostat switching off the immersion is causing the trip, but this is just a switch which opens. Unless it is internally faulty and the action of the contacts opening causes it to earth to the tank it shouldn't make it trip.

The thermostats are available separately from places like the depot and only cost £10. Would be easy to eliminate.

 

[diverdan74]

New Stat

• diverdan74
• 30 Aug 2010
• 1

Here's a pic of the new stat. Think wiring is ok.

Definitely MCB not RCD

Tried the test flameport suggested, stat set to min, switched it on, it tripped the mcb, turned up the stat powered it back up switched it on, fine! Left it 30mins, switched off turned stat to min switched it back on, fine!?! One hour later it trips!!!!!!
Must be the element?

 

[flameport]

As unlikely as it seems, it appears to be the thermostat causing an intermittent short to earth somehow.
With the stat at minimum, it would be open, and therefore the element would not be connected.

With the multimeter you have, the only way to check this will be to remove the thermostat and check for continuity between the terminals and the metal stem while rotating the temperature adjustment. Any continuity reading indicates the thermostat is faulty.

Other things from the picture:
The flex is supposed to be secured in the grip at the top right, the bar and screws are missing.
That thermostat has a very large top, almost too big to fit in there.
The cylinder looks to be as old as the hills.

 

[JohnD]

have you got a clamp meter to check the actual current drain? just wondering if it might be a non-standard element

it's odd that the cable doesn't look like it would fit easily. have you got the plastic cap, and does it show the make and rating of the element?

 

[diverdan74]

The element is rated at 3kw from the metal cap, not sure of make, there's a wickes box with the old element in so if that's any help?

The new stat is a bit tight to get pass to neutral terminal but does still slot in, i removed the flex clamp to show the connections, the wires are not on best route but none are touching when clamped.

Will check the continuity on the stat but don't have a clamp meter.

It is as old as that's why i don't want to take the new element out again!!!

 

[Darren1234]

I'm with Flameport here, it sounds like your Thermostat is internally faulty.
When it switches the supply off it shorts to earth (tank) somehow.

Get a new one and replace just that bit, not the coil, I don't know if you've removed it before but its just dropped inside a tube. You don't have to get the whole element out to change it.

Sods law I threw my old one out 3 days ago after it packed up so could've pictured it for you .

Edit :Since when was sod a swear word?

 

[ban-all-sheds]

Since the people in charge decided that it was no longer a word meaning a piece of turf, or surface soil held together by grass & roots, and that one of the traditional terms for Ireland, used particularly by descendants of emigrants, is in fact an obscenity.

They're wrong, of course, as they always are, and are contributing to the destruction of the English language, but hey - that's a small price to pay for the prevention of the use of such disgusting words.

Isn't it?

And think how cheap dictionaries will become as they get thinner and thinner via the deletion of all the alternative meanings of words.

 

[JohnD]

I understand it is a long-established word for a Sodomite and is still sometimes used as a term of abuse

5,000 years ago the Israelites thought that the inhabitants of the city of Sodom habitually indulged in undesirable or unhygenic sexual practices (as well as other sins such as overeating and pride) and they were therefore punished by God, possibly by a volcanic eruption since fire and brimstone are mentioned. I do not know if the river Jordan is in a volcanic region.

 

[ban-all-sheds]

I understand it is a long-established word for a Sodomite and is still sometimes used as a term of abuse.

I don't think the imputation is that today.

And yes, one meaning is a term of abuse. Or wry admiration, as in "you lucky ***".

The point is that it isn't always a term of abuse, and therefore should not be automatically censored.

 

[ban-all-sheds]

I understand it is a long-established word for a Sodomite and is still sometimes used as a term of abuse.

What's Moderator 11's understanding of it?