Overheating Immersion Heater

[Moonraker]

Thanks for your patience guys, I do appreciate it. Doc, no, I haven't used the boiler timer switch in years - not since 2005 - to control either the domestic supply or central heating, both control levers are most definitely OFF nearly all the time - except when I make a point of turning them on.  When the latest stat is fitted tomorrow, I'll do what Sellers suggests and report back. Incidentally, after the latest scare, I turned the boiler stat on the cylinder down five days ago and then had a luke-warm bath!

Moonraker

 

[ProDave]

Thanks for your patience guys, I do appreciate it. Doc, no, I haven't used the boiler timer switch in years - not since 2005 - to control either the domestic supply or central heating, both control levers are most definitely OFF nearly all the time - except when I make a point of turning them on.  When the latest stat is fitted tomorrow, I'll do what Sellers suggests and report back. Incidentally, after the latest scare, I turned the boiler stat on the cylinder down five days ago and then had a luke-warm bath!

Moonraker

Which suggests the boiler IS heating the hot water.

 

[SPECIAL LOCATION]

There has got to be something else we are not being told here.....

1/  Who in their right mind would even contemplate burning money to operate an electric immersion heater, when they have a correctly functioning boiler that can heat the water at a much cheaper cost??

(or did you stop using the boiler due to a wiring fault in the past that a plumber couldn't fix??)

Even if you don't want to heat the house via radiators....   {which TBH is also a no brainer "Central Heating -vs- Electric fire"..

as you can still turn off radiators in rooms you don't want to heat!}

It would save you money by heating the water from your boiler...

2/

IF YOUR HEATING IS WIRED AS WHATS KNOW AS Y_PLAN.....

An incorrectly wired y-plan heating system could be putting a live from your hot water OFF though the cylinder thermostat to fire the boiler..

Hot water ON & Hot water OFF both output a live signal from the program timer, through the central heating control wires if wired as Y-Plan..

So Hot water switch in OFF can still put a live to the boiler if other faults in the wiring center or 3-port valve..

You need a full investigation of both the immersion heater wiring AND the central heating wiring IMHO..

the symptoms you describe and the actions already taken imply that you could be missing testing something correctly..

and from that wrong assumptions are being made as to the cause.

 

[ProDave]

Another point about 3 port valves, is the "hot water only" position of the valve is with it completely de energised.

So if the motor in the actuator has burned out, the 3 port valve will be stuck heating the water tank, and the cylinder thermostat will have no effect.

3 port valves are not fail safe in this respect, which is why I much prefer two 2 port valves instead.

 

[Moonraker]

Yes, the boiler does heat the hot water but in my ignorance I didn't realise that this is cheaper than using the immersion. Clicking the boiler thermostat backwards and forwards confirms that it is controlling the boiler.

I also assumed - wrongly, apparently - that on a mild winter day having one bar of an electric fire on for two or three hours is cheaper than having fully on three rads in a large living-cum-dining room and five more elsewhere. Rads in rooms I don't use much are usually turned almost off except during cold spells.

If the wiring is incorrect then it's been incorrect for almost 35 years, yet the problem under discussion has only been with me for three months. Before that, the last time anyone played with the wiring was when I fitted a new element and stat two years ago. Since then both have been replaced by British Gas.

I am 100% convinced that the boiler only fires when I set its controls in the kitchen to do so.

The other development is that the "red arrow adjuster" in the week-old immersion stat can be moved through two complete circles, rather than the 300 degrees or so of previous, similar stats. Something wrong there, perhaps? And no, I didn't force it. (British Gas is replacing it again this afternoon.)

Moonraker

 

[ProDave]

If you are worried at heating the whole house, fit thermostatic valves to all the radiators, so you can set the temperature for each room and turn unused rooms right down to nothing (or just frost protection)

 

[Steve3948]

Some Imm Thermostats are locked in position at something like 50 degrees, trying to alter breaks them. There are some really rubbish ones out there and a good quality one is worth paying extra for.

 

[ruthiee]

Hi moonraker. I've been reading your postings with great sympathy. I also had a complete thermostat and immersion heater unit fitted at the beginning of the summer - after just 2 months the thermostat has broken and the water is boiling hot( after Econ 7 heats its at  night

). This is the second time it's happened in about 18 months. it's a copper cylinder boiler too. Not sure if it's vented but I can find out.

I also have central heating - oil - and didn't realise that econ 7 electric is an expensive way to heat water. I use the airing cupboard with the boiler to air clothes, but I guess I could just air them by the radiators just as well.( I DON'T tumble dry as I do know that's a very expensive thing to do). Now thermostat is broken, is it safe to have central heating on to heat water? Sorry but I am completely ignorant about all this.

 

[wozz]

Yes it's fine the tempreture  of the tank should be controlled by a tank stat which has nothing to do with the immersion heater.

It's worth getting it fixed should be cheap and easy as there's always a chance you could run out of or have your oil stolen. Not so much of a problem with gas. 

 

[Bruspark]

• I suspect that the boiler water control valve to the water tank is furred up or jammed so that there is always a small flow of boiler water into the tank coil.  Over a number of hours this will heat the tank to the boiler flow temperature  (typically 70c or more) rather than what the immersion heater is set to cut off at (typically 55 - 60 at tank top)

It is however lamentable if BG didn't check this given the symptoms reported