immersion heater trips mcb

[dfub]

Hi all,

I have a copper hot water storage tank, that is heated by an immersion heater that we turn on and off when we need it. This is the only hot water system we have, no gas central heating etc.

When i switched it on today it tripped the mcb (plug-in wylex). So i reset the switch and tried again, it tripped again.

I( unscrewed the switch on the wall and checked the wiring, it is all secure and earthed.

I suppose there are a number of things that could cause this but i wondered if anyone knew of any common occurences that it might be. Might it be busted heating element? I am reasonably competent at DIY, if it was this, could i change it myself?


Thanks for any help you can offer.

 

[RMS]

You might have a dead short on the element, if you have a continuity tester then you should be able to test it. Imerssion elements for a domestic tank normally give a reading anything between 10-20ohms depending on the size.

 

[RF Lighting]

Sometimes imm htr elements go open circuit across the coil when they fail, but in the process end up with either a physical short to the body of the element, or a short though the water they are immersed into. As RMS says try (with the SWITCH turned OFF) a continuity test between the live and neutral connections on the heater element (after the rod stat), then test from live to earth, then neutral to earth, If the element is ok you should get a reading between live and neutral, and NO reading between live or neutral to earth. If you do need to replace the heater they can be an absoloute t**t to start unscrewing but the rest is fairly straight forward. (dont forget to drain the cylinder first (not just the header tank))

HTH

Rob

 

[RMS]

Would never have thought to check continuity between live+earth and neutral+earth in the event of the element failing. Learn something new every day, thanks RF.

 

[cozycats]

I understand the trick is to get 'movement' on removing the old heater BEFORE draining the tank. The weight of the water helps to prevent just twisting the tank up!!!

 

[RF Lighting]

Ahhhh nice trick. I will try that. I have a meter of scaffolding to fit on the end of my imm heater spanner, and a ruddy great hammer Once split a cylinder though

 

[comms]

And don't drain to much water out of the tank before undoing the element or it may collapse on itself so I was told by my plummer.

 

[dfub]

Thanks for the tips, will try them out tomorrow. I'll let you know how i get on.

Thanks again.

 

[dfub]

Well, it does seem to be the element, so i have set about trying to unscrew it (with the tank full). I can't one bit of movement on it, so i am going to buy a 'box spanner' with a bar that you grip form the top, hopefully that'll do the job. Anyone got a number for an emergency plumber....

 

[RF Lighting]

A box spanner will do a much better job than the cheaper ring type ones. You can also use a bit of metal bar to extend the handle and give you more turning force, but be careful not to split the cylinder if you are a bit too forceful. Another trick to try is to heat the cylinder aronund the element to try and get the metal to expand around the thread.

 

[dfub]

gasp...gasp... Well i finally got it to give, a mixture of box spanner, hairdryer and hammer!!

It is a 26" long element, can i just pick one up at B+Q? I'm not really bothered about getting the cheapest price, just need somehwere with a good returns policy after i *rse it up


Thanks for all the help in this thread

DF

 

[JohnD]

Go somewhere has has two or three grades, the more expensive ones will be marked as resistant to aggressive water (depending what you have in your area might be incalloy or titanium sheathed or something).

A plumbers or electricians merchant ought to know what is best suited to local conditions (hard or soft water).

I prefer the dual element (long "bath" short "sink") but they are not widely available.

Be sure to top up the cylinder and pipe insulation while you're working in there.

 

[dfub]

I'll check out the local plumbers merchant then. thanks for the heads up on insulation too!

 

[dfub]

well, got my new heater fitted, filled the tank and switched it on, hooray, it didn't trip the electrics!!

But what's this?.....is it a leak? aaaarrgghhhh!!!

There are 2 small leaks in the cylinder itself (near to, but not on the seal the the heater) One forms a drop of water but doesn't go any further, the other forms a drop and then runs down the tank.

What is the best way to seal these? I can't afford a new tank at the minute so i need a patch job, what can anybody recommend?

 

[JohnD]

Fernox LSX.