Immersion heater continuously blowing fuses

[wobblywilly]

Hi All,

I've got some trouble with my immersion heater and I'm hoping someone on here can save me the expense of getting in a tradesman to fix it as I believe that there is something simple wrong with it.

The problem is that the immersion heater is blowing fuses at the consumer unit continuously - as soon as the fuse is inserted and the switch is pressed, it blows - I can see the flash of the fuse blowing.

I have the immersion switch turned off when I insert the fuse. All is well until the immersion is turned on and it is then that the fuse blows.

The fuse being used is a 15A cartridge type - it is a direct replacement for what was in previuosly.

I have checked the 13A fuse at the actual heater and it seems fine. There have been no modifications or upheaval around the circuit which could have caused this problem.

Does anyone have an idea as to what could be causing the problem. At a guess I would say that the circuit is trying to pull (sink?) more current than the fuse will allow (15A) and therefore the fuse blows. But why is this happening now?

Any ideas?

Cheers.

Willy.

 

[Careful_Bodger]

Your immersion heater has probably failed. They can corrode & the innards then get exposed to the water. This blows the fuse. (Well, it did in my case.)
If you can buy or borrow an immersion heater spanner (this fits the large hex nut at the top of the element) then you can have a look. Take care not to distort the tank metal though - it is a bit thin. It it best not to drain the hot water tank entirely, as this provides support. If the casing of the heater element looks 'blown' then this is the problem.

Then you can buy yourself a new element e.g. http://www.screwfix.com/app/sfd/cat/pro.jsp?id=63692&ts=00538

Reasonably simple job - if you know what's what.

 

[Careful_Bodger]

Aha - found some images of the appropriate tool....

or

 

[Damocles]

Um, I am just a teeny weeny bit concerned why the 13A cartridge at the immersion end does not blow while the 15A cartridge at the CU does. This does suggest that the current which blows the 15a is not going through the 13A. I am imagining that the 13A is in a connection unit with switch to which the immersion is connected?

The speed of theses things blowing is not an exact science, but this sounds a bit fishy. If tken at face value, it could suggest wires shorted inside the switch. Perhaps rubber flex to the immersion which has perished?

I would suggest that some more careful fault finding is called for before going ahead and removing the immersion heater. Also, if it has failed, buy a new one before taking out the old one. And expect it to be stuck.

 

[comms]

Had the same problem sometime ago, it was down to a pinprick size hole in the area of the element housing so the contacts were earthing out.
so before draining the tank take the cover off of the element connections & check for water there.

 

[andy]

disconnect the immersion heater from the FCU (or whatever it is connected to) and see if it still blows the fuse. if it doesnt then more than likely the heater is at fault, if it does then you have a problem before the heater

 

[Careful_Bodger]

Hmm - you might be right Dam, but what is the fusing current tolerance range on a 13A fuse compared to the tolerance range of the 15A?

..still - I reckon it is a blown element, subject to Andrew's fault finding suggestion!!!!!

 

[breezer]

i bet the 15 A fuse goes before the 13A fuse does because the 13A fuse is for a plug top and the 15 a i will bet is a hrc, they tend to be slightly quicker

 

[Damocles]

Makes you wonder who designed the system of fuses to ensure discrimination. Know exactly what you mean, though the post said the 13A has now been overloaded several times without blowing.

 

[Lectrician]

You will have to drain down the tank if it is an element in the bottom (side entry, not top).

This is not just a matter of turning off the mains, and running the hot tap until it stops either!

 

[JerryD]

Yes, how many people think that as soon as the hot tap stops running "It must be drained down"

Then they remove the immersion........................... get a mop "QUICK"

 

[ban-all-sheds]

Few tips re removing IHs.

1) If there isn't clearance for a spanner, a G clamp can be a life-saver.

2) With a felt-tip pen, draw a line on one face of the hex head of the IH crossing over onto the cylinder. When starting to undo it, tap the handle or tommy bar of the spanner with a hammer - the vibration can be useful to loosen a stuck thread. If the IH starts to turn but the FTP marks stay lined up then stop, as you are twisting the metal of the cylinder, and before much of that it will tear.

3) If the IH won't loosen easily, try a couple of taps in a clockwise direction - that can often break the seal.

 

[mapj1]

More tips - yes, the immersion element is almost certainly dead. You will realise, after the effort of getting it out, that it is worth paying a bit more for the "long life" corrosion resistant ones - the cheapest of the cheap can rot through in less than 3 years.
Before you drain down, use the immersion spanner and club hammer to try to crack the gunge sealing the thread - the having the water still there stiffens the tank against creasing. Only once it moves even the slightest, turn off the feed from above (or tie up the ball-valve with a bungee cord or similar, if the original installation doesn't include a stop valve in the feed pipe.) Then identify the drain at the bottom of the tank, and fit it to a hose pipe, and drain the tank down to the level of the heater. (if the heater is at the bottom this means all the tank.)
Make sure you have enough tools to apply remarkable force, over time the heaters corrode in, and become extremely reticent. In extremis they can be cut out, but it takes great care not to damage the threads on the tank, and then getting the new one not to leak is damn nigh impossible, without resorting to methods like araldite, that make this change the last before the cylinder needs changing.
Good luck.
M.

 

[ban-all-sheds]

May we interest you in a combi boiler, sir?

Unlimited hot water - no wasteful loss of heat from a stored cylinder, regain a circuit from your CU, gain useful space in your bathroom & loft.

 

[ban-all-sheds]

getting the new one not to leak is damn nigh impossible, without resorting to methods like araldite

I've never had to solve this problem, so I don't know if this would work, but what about Hermatite? It's not as if it has to withstand great temperature & pressure...