Immersion cut out

20 Apr 2017
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United Kingdom
Hi all,
I have a standard vented copper hot water cylinder, less than a year old, with one immersion for hot water only, no boiler. The immersion heater has a cut out in the body of the immersion and a separate thermostat. The cut out keeps tripping for no apparent reason. The thermostat clicks on and off at the right temperature, but sometimes, maybe once every couple of days, the cut out will trip and need to be reset. The stat has been changed already. Maybe the new thermostat sometimes sticks or maybe the cut out is faulty. Either way, instead of replacing the whole immersion, could I just buy an 18" thermostat with a built in cut out and then wire it to the immersion without going through the original cut out? Or am I missing something? The plumber who fitted it is AWOL. Any advice appreciated.
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The cut out is because a thermal plastic header tank can warp and split if the immersion thermostat sticks, if there is only one form of heating then the cut out is not normally resettable, once it trips you change whole thermostat, once when there are more than one form of heating is there a reset button so should the solid fuel heating cause the over heating then you don't need to change thermostat for immersion heater, if the header tank is thermal setting plastic or metal then it is not really that important, only with thermal plastic can it split.

There have been at least two deaths, one was a baby, the other Emma Shaw although not directly due to thermostat fault, but the thermostat fault started a chain of events.

is the problem read more here why they are permitted to make the tanks out of thermal plastic I don't know.
if you can lay your hands on a thermometer, find out what the actual temperature of the water is when the cutout activates. What is your thermostat set to?

btw, regardless of a plastic tank, overheated tapwater can scald, and is particularly dangerous to babies, small children, and the disabled or infirm. Scalding injuries in care homes and hospitals were more common before blender valves were installed.
Thermostat is set to the original setting under a dot of paint, about 60 I think. Cuts out at different temperatures
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Thanks for the replies so far and I realise the importance of hot water safety, but I still need to know whether I can replace the thermostat and cutout for a dual thermostat that does both?
1. Not entirely clear but it appears to me you have an immersion heater with a built in overheat thermostat and the usual pocket tube for a normal, temperature regulating, self resetting, thermostat.
2. You want to know if replacing the existing resettable thermostat with a new one which has the overheat thermostat built in (as well as the resettable one).
If the above is correct, then doing what you want to do maintains the safety element of the overheat thermostat.
Whether it will solve your problem is a different issue.
It would help if you put up a photograph of the immersion heater with its cap removed showing the two existing thermostats.
1. That's correct
2. Yes
Hopefully it will do the trick, I don't see how it wouldn't. Unless the new stat is faulty.
I've got a TS230 Dual Safety Thermostat as a replacement. Is this ok? All I have to do is wire straight into the new stat, missing out the cut out.
Have you confirmed any electrical testing?
Have you confirmed any electrical testing?
Yes the stat and cut out have continuity/no continuity when they are below or above limit. The cut out seems to go randomly. Also the supply is fine.
Oldbuffer, maybe you're right and the problem is elsewhere. The new thermostat now cuts out, so I'm guessing this is a plumbing problem, not an electrical one. Is there anything that would cause an increase in temperature enough to trip a cut out? I don't understand how the thermostat can be set to 55 or 60 and the cut out can still trip. It can't be 3 faulty thermostats or cut outs surely ...
could be that the element itself is heavily scaled up, I have seeen that causing OH ststs to operate prematurely before
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