Possibly pointless immersion heater - can I turn it off?

Whilst investigating other heating and plumbing related things I've never previously needed to care about, I realize my tank has an immersion heater, on the photo below. It's been turned on at its socket on the left of the image all 7 years I've been here, but during times the boiler hasn't worked recently/last winter, I've had no hot water - which is why I'd never thought about it before.

Is there a point to it, and it being on? Am I wasting electricity? I presume not as I guess it's intelligent enough to turn itself off once the water is hot enough - which it is since the boiler heats it instead. And that'd be assuming it worked anyway, which evidence suggests it does not so perhaps it's using nothing at all.

If you don't have hot water when the boiler is off, then it's not working, and won't be using electricity. If the heater has been left 'on' permanently then the element will most likely have failed by now anyway. However, the switch by the hot water cylinder isn't always the only one; there is often a second switch elsewhere like the one below, often in the Kitchen.



In which case both switches must be on for the heater to work, and the one next to the immersion heater is for isolation during maintenance, and would normally be left on, and the other switch used for control.

There may also be a timeswitch somewhere that is controlling it, but you would normally be aware of that.

Heating water with electricity cost about 3 times more than using gas, unless you have an 'off peak' supply on a cheaper rate. An electric immersion heater fitted to a hot water cylinder heated by a boiler is really only there as a back up, for when the boiler fails.

Michael F H said:

Is there a point to it, and it being on? Am I wasting electricity? I presume not as I guess it's intelligent enough to turn itself off once the water is hot enough - which it is since the boiler heats it instead. And that'd be assuming it worked anyway, which evidence suggests it does not so perhaps it's using nothing at all.

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If it's not working at all, ever, then it is using no power. So turn it off or not - it will make no difference. It could be that the over heat trip has tripped on the thermostat - a simple push button fix, then you would have it as a useful standby for your boiler.

Aside from the above possibility of a second switch, there might be a time clock controlling when the immersion heater comes on, plus an MCB at the consumer unit which needs to be on too.

When your boiler is out of action the immersion is a back up ,would it not make sense to investigate why it's not working and have it put into working order ?

terryplumb said:

When your boiler is out of action the immersion is a back up ,would it not make sense to investigate why it's not working and have it put into working order ?

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Yes, it probably would. Fortunately the boiler is working again now but that's no reason no to address this. Looking at the other comments above I've done a bit further looking around and noticed a few things.

1) The black knob on the top of the tank which is the immersion's "head" (for want of a better word) is hot.

2) Under the wall-hanging the boiler downstairs there's a switch, right next to a pair of double sockets. It has no light but it is turned on, and there's a fuse access within the front panel. Although it seems more like this is the fuse and socket for the boiler than the immersion. I can find nothing else like a second switch for the immersion.

a cylinder with yellow insulation is something like 30 years old, so the immersion heater may well have failed by now, especially if it was left constantly turned on. Or it might be the thermostat, which is an easier and cheaper fix. Modern immersion elements are fitted with an improved thermostat which has a seconday overheat cutout to prevent dangerous scalding accidents which have occurred in the past.

BTW an immersion heater will (should) be on its own circuit, with a 15A fuse (often blue) or a 16A breaker in the consumer unit (fusebox). This might have been turned off or taken out. It is rare for a fuse to blow.

Michael F H said:

The black knob on the top of the tank which is the immersion's "head" (for want of a better word) is hot.

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That will be because of the hot water stored in the cylinder below it. The elbow located behind it will likewise be hot for the same reason. Even if it was working, there is nothing in the "head" to create heat. The actual electric heating part is immersed in the water down below; hence the term immersion heater. Only the thermostat and wiring connections are under the cover.

Michael F H said:

Under the wall-hanging the boiler downstairs there's a switch, right next to a pair of double sockets. It has no light but it is turned on, and there's a fuse access within the front panel. Although it seems more like this is the fuse and socket for the boiler than the immersion. I can find nothing else like a second switch for the immersion.

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That does sounds like the FCU for the boiler. There may not be a second switch fitted, especially if the immersion heater is really only there as an emergency back up. In which case it would appear to have been inadvertently left permanently 'on' and has worn itself out.

However, I once attended a property to investigate a similar scenario as yours, there was a MCB which was live, as was the cable leaving it, but the switch at the hot water cylinder was dead. After much searching / tracing of wires a second switch was found. A previous owner had fitted a kitchen wall cupboard over it and it was switched off.