Immersion Heater

[moosehead]

Looking for some [more] advice.

I have had two heater elements blow in an emersion heater within three years. Is this an unusual phenomenon? (The tank/emersions were replaced three years ago.)

Should the emersion be on a separate circuit, currently it is on a ring?

 

[kai]

Firstly - do you have a Fuse-connection unit protecting both Top and Bottom Elements, both containing a 13 amp fuse in?

Is the Thermostat working OK?

Is the Earthing present and of the correct size, and secure?

Is the earth loop resistance low enough for the 13 amp fuse?

If wired as above, the fuse will operate to protect your appliance, i.e. the immersion.

 

[Scoby_Beasley]

I was always told, in our hard water area (it threatens you as it comes out the tap ), that you use it or lose it as they coat up with limescale if you always rely on c/h to warm water apart from that "once" when the gas goes. But if you aint got c/h I'm bollixed !!

 

[mapj1]

The choice of fusing methods won't make the element last longer!
In any case a B type 16A MCB will always blow before a 13A fuse, at any overload, assuming both at the same temperature in both places.

In aggressive (acidic) water areas a cheap element can fail in under 18 months. Consider coughing up for an incalloy one, with a 5 year anti-corrosion guarantee.
Also if the plumbing is mixed metal (iron and copper) you should have a sacrificial anode in the tank - it may have rotted off. A piece of aluminium or magnesium in good electrical (i.e. metallic) connection with the copper, but in the water will substitute if this is the case.
hope that helps M.

 

[towman]

I thought Immersions were supposed to be wired on their own radial circuits and not onto the ring main? Not that I think that would make any difference to how long the element lasted - though I suppose if there was a significant voltage drop the element ends up being on longer to warm the water up?

 

[moosehead]

Thanks for the advice guys.

Current is not protected by FCU's but by the boards MCB's.

My belief is that thermos may not be working properly, although the surge which tripped everything this morning was the timer clicking in.

We are in a hard water area and we use immersion to pre-heat during eco7 timing.

Not sure about earth loop resistance so cannot comment.

It may be low price components causing the problem so will try to upgrade - next question what would be the best, most reliable makes to buy and what should I be careful of when undoing the old elements? (Professionals can assume the tank is empty!)

I will also put the immersion on it's own circuit.

 

[mapj1]

Make sure you have the right big spanner, and are equipped to drain the tank.

http://www.tlc-direct.co.uk/Main_Index/Water_Heating_Index/Immersion_Heaters_4/index.html

Do not drain the tank until you have made the heater turn a little in the undo-ing direction, you may need to hammer the spanner to crack the seal, and the mass of water stops the cylinder from creasing as you do this.
Then drain the tank, and remove the element and thermostat as an assembly. (This is like those diy books where it says "unscrew the flywheel nuts and place the fly wheel to one side".
What is meant is "spend an afternoon applying progressivly more unreasonable force, bending your best tools and skinning your knuckles, then when it finally comes free, remove and place the flywheel to one side"....)
Take the old one to your plumbers merchant and ask for a 'long life 'or "incalloy" version of the same thing. Stay clear of anything witha short guarantee period.
this sort of thing is OK.
http://www.tlc-direct.co.uk/Main_Index/Water_Heating_Index/Immersion_Heaters_1/index.html

The thermostat itself can be removed 'dry' as it sits in a tube that goes into the water volume, I'm assuming the heating element is open circuit.
For the last 20yrs or so, immersions have been recommeneded not to be on the same circuit as anything else, as they mop up a lot of the capacity of the ring, but if you have not expereinced nuisence tripping yet, its not a big problem, and not the cause of your element failure. However, when the chance arises, yes, split it off onto its own circuit. A 16A MCB will be fine.
Do not overlook the possibility of a loss of sacrificial anode - it makes a huge difference to the rate at which things rot.
Use PTFE tape on the new one, and be careful not to damage the threads in the tank itself.
regards M.

 

[Scoby_Beasley]

Then drain the tank, and remove the element and thermostat as an assembly. (This is like those diy books where it says "unscrew the flywheel nuts and place the fly wheel to one side".
What is meant is "spend an afternoon applying progressivly more unreasonable force, bending your best tools and skinning your knuckles, then when it finally comes free, remove and place the flywheel to one side"....)

So succinctly and eloquently and 100% accurately put map ! Remember if it can go wrong............

 

[moosehead]

Free champagne to the troops at Cheltenham when I complete my sparky course (just kidding, 43 and embalmed in what I do).

The mass of water prevents creasing tip is one that would never appear in a DIY book but exactly what I was afraid of. Will add a touch of WD40 for good measure!

Will look for top quality replacement parts and hopefully that will fix the fault .

Thanks to one and all for the friendly advice - happy sparking!

 

[mapj1]

after-thought.
pictures of the 'easy' job are here..http://www.readersdigest.co.uk/diy/webpages/340_341.htm
You might wish to have some old towels around when you do finally get the heater to turn with water in the tank. You may also wish to ask those of a delicate disposition to stand out of earshot of the professional language.
If the tank starts to crease, and doesn not recover shape once you relax the spanner, stop immediately, and drain it down. A fair bit of elastic flexing (i.e. it recovers) of the metal is not a cause for concern however.
Beware of jointing compounds that set solid - these may need to be blowtorched off with the tank empty.
Or it may all go really easily, occasionally they do, particularly if not that old.
M.

 

[Lectrician]

Advice above spot on.

The circuit to feed the immersion doesnt required an FCU, just a 20amp DP switch if fed directly from the board on a 16amp breaker, and 2.5mm cable (usually, although volt drop etc may require a large cable).

You use the Immersion for Econ7?? Does this element not come from a switched CU?? Do you have a 24hr time clock adjacent the tank??

 

[moosehead]

Lec - have a 24 hr clock - 05.00 to 07.00 = morning burn up.

 

[Lectrician]

Is that good economy for econ7? - assume you also have rads on the econ7??

 

[ban-all-sheds]

A couple more tips re removing the old element:

1) A G clamp (metal screw type, not quick-release plastic jobbie) can be used as an improvised spanner if you can't get access to use a proper one.

2) As was said above, take great care to closely observe the tank where the element screws in. If it's stuck, and the tank is old and thin it is possible to tear the tank, and this is a Bad Thing™. Use a felt-tip pen to draw a line across the element/tank join so that you can easily see if when you think it's turning it really is. But if it's only been in 3 years you should be fine.

 

[felix]

A piece of aluminium or magnesium in good electrical (i.e. metallic) connection with the copper, but in the water will substitute if this is the case.

If it's going to function as an anode it has to have an electrical connection to the tank. It's the potential difference set up between copper and magnesium that protects the copper. A piece of magnesium lying on the bottom will only work if it's not insulated from the copper by lime scale.