Immersion heater bust

G_M

The immersion heater just stopped heating the tank. One day it did, next day it didn't.

I've checked all wiring and the fault must be the heater (why don't they have a little red light or something to to show when they come on....)

Might it be the thermostat and can these be changed?
If it's the heater element, how easy is this to change?
Why does the online guide I saw say you need to drain the cylinder? The immersion heater is located right at the top.

DVardysShadow

G_M wrote: »

The immersion heater just stopped heating the tank. One day it did, next day it didn't.

I've checked all wiring and the fault must be the heater (why don't they have a little red light or something to to show when they come on....)

1. Might it be the thermostat and can these be changed?
2. If it's the heater element, how easy is this to change?
3. Why does the online guide I saw say you need to drain the cylinder? The immersion heater is located right at the top.

1. Yes, it could be the thermostat and these can be changed easily and are quite cheap - less than £5. You do need the right one see http://www.tlc-direct.co.uk/Main_Index/Water_Heating_Index/Immersion_Heaters_2/index.html for some idea of the choice.
2. The element is simple to change in concept, the difficulty is shifting it in the first place. Correct tool see http://www.tlc-direct.co.uk/Main_Index/Water_Heating_Index/Immersion_Heaters_4/index.html. You can easily buckle the tank if you apply force off centre. For that reason, I prefer the box spanner.
3. You need to drain down because the header tank is at a much higher level. I would leave the water undrained until the element has been shifted a little, as the extra pressure provides a little bit more pressure to keep the tank in shape

macman

You say that you've 'checked the wiring'. It may be visually intact, but have you used actually tested the circuit to ensure that power is getting to the terminals on the head of the immersion? Don't do this unless you know how to do so safely.

G_M

Unusually (please! No discussion on this point!) there is a (dedicated) socket in the airing cupboard (and separate RCD on the fuse box).
The heater is connected via wire to a plug which goes in the socket. The socket works. The fuse in the plug works. I cannot believe there is suddenly a problem with the wire (yup - I even checked for mice teeth marks along the wire!).

So that leaves the thermostat or the heater itself (unless I'm missing a trick somewhere.....)

I note that thermostats cost around £7, whereas a whole new heater including thermostat is around £10. Given there's so little in it, is it worth changing the stat and maybe finding that doesn't solve it and have to change the heater anyway....

On other hand, looks like the stat can be changed without draining down/struggling with potentially tight heater........

Thoughts?

macman

Unlikely, but yes, the cable could have failed-immersions require a special heat proof cable, not standard circuit cable.
As I said, you've not established that power is available at the heater terminals, which is the first thing that an electrician would check.
But if you want to DIY, the cheapest option is to change the stat yourself and hope that is the source of the fault. If it isn't, you're only £7 down.

mikey72

Leave the tank full if you're taking out the heater.
I've had to use a three pound lump hammer on at least one, and bent the spanner well out of shape years ago.
The water helps keep the tank in shape.
I don't usually drain down, I just turn off the valve from the header tank, open the downstairs tap, and then catch the water that's left with towels.
You have to believe it will eventually stop.

Make sure you don't cross thread the new one going in.

DVardysShadow

G_M wrote: »

I note that thermostats cost around £7, whereas a whole new heater including thermostat is around £10. Given there's so little in it, is it worth changing the stat and maybe finding that doesn't solve it and have to change the heater anyway....

On other hand, looks like the stat can be changed without draining down/struggling with potentially tight heater........

Thoughts?

The extra cost of the immersion is trivial, I'll agree. You could try whether the immersion is moveable. If it is, I would change it. But if it is hard going, I would try just the stat first.

G_M

Many thanks all.

1st prize goes to macman - I drained off the top gallon or so and then unscrewed the heater cover..... to find one wire burnt through.

Swapped the cable for a 1.5mm heat-resistant flex, connected up, refilled and took a nice hot shower!

macman

Pure guesswork I assure you-what do I win? An immersion heater spanner?

G_M

Too late! I had bought one in preparation but returned it today.

You can have a free shower next time you're passing though!