What is this switch in my airing cupboard

5 Apr 2010
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United Kingdom

This may seem like a silly question but I have two switches on the wall in my airing cupboard - one is the power shower switch, what is the other one (it has a cable that goes into the top of the water tank)?

I haven't had any hot water through the shower for a few days (though the power is on and all other taps, including the tub's, are fine) - could it be that I turned off the wrong switch by accident when I meant to turn off the power shower the other day, and cut off the hot water supply to the shower instead?

Many thanks.

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Hi lightning. Please can you expand? If I turned it off in error then how come I still had hot water everywhere else in the house, but not through the shower?

Sorry I know nothing about heating systems :]

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Immersion is basically an overgrown kettle element that heats the contents of the hot water cylinder. Does the cylinder feel hot to the touch? If unsure, run some hot water off via a tap, until you feel hot water coming through, then check the pipe from the top of the cylinder. Is this pipe hot?

Do you have a gas (or oil) boiler? If so make and model would be useful.
Thanks Hugh. I turned that switch back to 'on', and yes, I now have hot water through the shower, also unusually SCALDING hot water coming out of the kitchen tap.

I have an old gas boiler, Glow Worm Space Saver38. It is temperamental anyway, seems to heat all day when I turn the dial to twice a day and vice versa.
Firstly, for safety's sake if the water is that hot, I would turn the immersion off again. It is possible the thermostat may have failed, this would lead to the cylinder contents boiling, and can (and has) lead to catastrophic results.....

Meanwhile, the boiler should be capable of heating the cylinder for hot water. If there is a thermostat on the cylinder (It'll be strapped to the side, about 1/3rd of the way up from the bottom), check this is set at about 60deg C.

If you find you run out of hot water then the boiler side of things will need looking at asap to get you some hot water. I would stress the immersion is better not used until it is checked by a plumber.

From your description it is probably a faulty programmer/timeswitch that is causing the boiler to work intermittently. The old boilers either work or dont, in this case it will only work when the system is supplying power, which will come via the timeswitch.
Just checked the water again and it has never been - and shouldn't be - that hot! The pipe leading to the cylinder is also VERY hot. I've turned the switch off again as per your advice, but can't find a thermostat on the cylinder.

The immersion switch should have been on in the first place, right? I never turned it off knowingly, I can only assume I turned it off by accident last Wednesday which is when I noticed the problem with the shower. Or am I getting confused?

Also why turning it back on would cause the cylinder to overheat?

In any case, the advice is call a plumber first thing tomorrow, yeah?

Under normal circumstances the boiler should heat the hot water. The immersion is provided for backup in case of boiler breakdown. Normally, leave the immersion off, its not needed as the boiler will be heating the hot water, (its also cheaper!).

In the event of boiler breakdown you can then use the immersion to get some hot water pending boiler issues being resolved. There may not be a 'stat' on the cylinder controlling the boiler, it depends on the type of system you have installed.

I would switch the immersion off and see what happens. If you have hot water still, (It'll take a few hours for the cylinder to go cold), then the immersion can be looked at when convenient. If you run out of hot water then that indicates a boiler issue which can be resolved at the same time as the immersion.

If need be, then you could do a test now to see if the boiler will provide you with hot water, if so then the immersion can be checked when convenient.

For safety's sake it's better not to use the immersion if the water is getting that hot until it is checked! There was an incident not too long ago where an immersion failed and boiled the contents of the cylinder. This in turn heated the contents of the cold water storage tank in the loft that fed the cylinder. Being plastic, the cold water tank softened, and collapsed, the contents of which came through the ceiling and fatally scalded a baby sleeping below. New immersions are now fitted with a safety cutout to prevent this happening, but if you have the older type then its unlikely to have a cutout.
Hmm, yes. Better not use it then.

Immersion off - I have hot water everywhere but the shower. I still don't get it.
Thats a shower pump, it will have to draw its supplies from the hot and cold tanks. Strange why all the other hot taps work but the shower doesnt... If there's hot water in the tank then for some reason its not getting to the shower. Check the isolating valve on the hot supply to the shower pump (Stuart Turner) hasn't been closed.
Oh, now that's getting a bit too technical for me. What would the valve look like?

I'm even more confused now I know about the immersion heater - shower worked fine with the immersion on (other than being too hot) and still okay now but the water in the cylinder is still very hot. Since last Wednesday and until I turned the immersion on earlier, I had hot water in the bath using the taps no probs, but only cold coming through the power shower.

Anyone know a good plumber in West Berkshire?

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