Immersion heater getting very hot

[pickledherring]

Our hot water is supplied by a stand alone immersion heater with a digital timer set to come on for 20 minutes in the morning and 20 minutes in the evening, using a digital immersion heater timer switch. We've used this set up for years without any problems. I should mention that the immersion heater element (3 kW) and digital timer switch were replacements made about 3 years ago as the old element and mechanical switch had both given up the ghost.

The problem recently seems to be that the water is now extremely hot coming out of the hot water taps and if you touch the exposed part of the heating element sticking out of the top of the tank it is scalding hot. This is rather surprising as the heating element only comes on for 2 x 20 minute periods in any 24 hour period. I don't understand why this should be.

Because the hot water tap (mixer type with single swivel spout) in the bathroom is getting so hot, it seems to cause the cold water tap to stop flowing. I'm just wondering if the extreme heat is causing some type of buckling in the cold water facet preventing flow.

So my questions are

i) What type of fault (if any) with the heating element would cause it to overheat?
ii) Does it sound plausible that the extreme heat could cause the cold water faucet to jam?

Thanks.

 

[JohnD]

it sounds like the thermostat has failed. This can lead to overheated or boilinmg water which can be dangerous. Is the cold water tank (probably in the loft) getting hot? Is it made of black plastic? Is it bulging?

Unless the immersion heater is so old that no available replacement will fit it, you can get a new stat and change it fairly easily at modest cost. It fits in a sealed tube so you do not need to drain water to change the stat, and it will not leak. If you are not used to this kind of work an electrician or a plumber can do it.

Please post photos of the cap of the heater to give us an idea of its age and make. The colour of the hot water cylinder also gives clues. There might be a label or markings on the top. You don't need to take the cap off yet, but if and when you do, you must turn off the electricity to the heater at the consumer unit first.

Thermostats come in different lengths so you need to inspect the old one, and possibly take it with you when you buy a new one.

I don't know why the cold tap should jam.

 

[oph]

Very possible that theres nothing wrong with the stat and that scale has built up sufficently enough around the sensor stat pod that the stat can no longer accuratly sense