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Problem with immersion heater staying on all the time

Postby nelsonbd » Sun Jan 01, 2017 3:11 pm


Noticed our immersion heater seems to be switched on all the time as the water is hot all the time (even though it is set to come up on 15 mins in the morning an evening). Water temp is about 62 degrees at the tap.

I have had a look at the heater element in it with a multimeter - its reading about 20ohms - which sounds ok. I also put the multi-meter across the thermostat (vkl3401 t100) - i can see as i switch the temp dial to around 65 degrees the resistance drops to about zero from 1800 ish. I can also hear it click at the 65 degree point.. I think that is normal behavior too?

There is an old mechanical timer (trac timer gp 24/7 & gpe 16amp) - is it likely to be the timer switch not turning the power off and on? Should i be looking at putting in a new timer?

I can supply pics if needed..


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Postby kbrownie » Mon Jan 02, 2017 1:04 pm

Yes sounds like the timer has gone faulty
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Postby ericmark » Mon Jan 02, 2017 3:28 pm

I have never really understood why timers are used with immersion heaters which are not powered by off peak power, well I suppose it could inhibit it running when the central is not running.

In the main immersion heaters work on temperature, the tank is so big and should be that well insulated that there is very little temperature drop unless water is drawn. So there are two reasons to use a timers.

One clearly when the power is cheaper at some time.
The second when central heating switches off at set times, and you don't want the electric being used when if you waited a little longer the central heating would do it a lot cheaper.

The normal method is to set the immersion heater temperature lower than the central heating temperature so the electric is only used when central heating is off.

Although likely there is a problem with the timer, it could also be auto synchronizing with central heating. i.e. it switches on so many hours after the central heating switches off.
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Postby nelsonbd » Mon Jan 02, 2017 10:46 pm

Sorry i should have mentioned i have a hot air heating system and it does not heat the water - well only a little bit (which i have never understood)..

So hot water is on timer to get hot water at correct times..


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