DIY Doctor

immersion heater thermostats

Postby tiptoe » Fri Aug 13, 2010 5:11 pm

Could anyone out there please tell me if there are any regulations that cover the temperature tolerances of immersion heater thermostats. We do not understand why there don't seem to be any rules as to their
accuracy, or any labeling on the products as to the temperature range one is expected to accept. I know what a well known supplier of thermostats finds acceptable because we have their letter saying so !!!! Are there any government ( health and safety ) regulations with regard to an item that is fundamental in controlling the water temperature. When set at 60 on the thermostat head, I would like to know whether I can expect a cold shower or make a cup of tea. HELP......
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Postby ericmark » Fri Aug 13, 2010 11:38 pm

TABLE 42.1
Temperature limit under normal load conditions for an
accessible part of equipment within arm's reach
Accessible part Material of
accessible surfaces Maximum
temperature (°C)
A hand-held part Metallic
Non-metallic 55
A part intended to
be touched but
not hand-held Metallic
Non-metallic 70
A part which need
not be touched
for normal operation Metallic
Non-metallic 80

Sorry it was in a table format but the point is the water out of the tap is non metallic and in direct contact with your hands so 65°C maximum. There could of course be a temperature reducer that mixes the hot and cold water. Since the tank can be touched and is metal top temperature is 80°C.

Google "" it is about a Water tank fault that scalded baby girl to death.

It has been standard now where the immersion heater is the only method of heating water that the thermostat has a non resettable over temperature device independent from main thermostat but where other forms of water heating are used this can trip the non resettable device when there is nothing wrong with the electrical system this is very important with solid fuel heating. Where solid fuel is used the header tank must be able to keep it's shape with boiling water. They are still plastic but a harder plastic.

The HSE issued this warning (Google "")

If you look for thermostats you will find this:- The Backermatic Safety thermostats listed below are manufactured to BS EN 60730: 2002/BS EN 60335 -2-73: 2002. BEAB approved. They incorporate a secondary resetable safety cut-out, which is independent of the main thermostat. The thermostats have a second set of contacts which open and limit the water temperature to 98°C should the primary thermostat fail.

I am sure you can find loads more with a google now I have pointed you in right direction.
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Postby sparx » Sat Aug 14, 2010 5:00 pm

hi, not to my knowledge, also older ones didn't have an overtemp. cut out as required now following a number of scalding deaths & injuries.
All new properties now are required to have mechanical temp. limiting devices on bath tap supplies for this reason.
If you store water at too low a temp.then there can be issues with legionella also inefficient use of tank volume so Gov. LABC look at controlling out put at taps instead,
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Postby ericmark » Mon Aug 16, 2010 12:27 pm

My fathers house built 1954 had an over temperature cut out which as a kid I was for ever resetting when the solid fuel cooker boiled the domestic water.

It seems it was a lot latter that cheap imports arrived which did not have the protection. There was then a move to use non resettable cut outs as it was feared people would reset cut out without correcting the fault. Seems the people writing the rules had completely missed the idea of having more than one form of water heating.

Of course with metal header tanks there was no problem if water did boil. It made a lot of noise and spat out water from overflow and could fill loft with steam if the builder had used chip board instead of proper wood to put tank on this could fail when wet but anyone not looking at why the water was making such a racket would be silly.

With the introduction of plastic tanks the problem started. These could bend out of shape and spill the contains when heated and needed extra protection. However there were also special tanks made for solid fuel cookers able to stand boiling water so to just say plastic tanks need non resettable cut outs is wrong.

What should have happened is flimsy plastic tanks for hot water systems should have been banned rather than to try to do something with thermostats. It has made it very hard now to buy a thermostat with a manual re-set which is of course needed with solid fuel heating.

The Ulster people have a different system with immersion heaters and it heats water in a side tank which then circulates heating the main cistern from the top down which means you get hot water very quickly after being switched on and it heats whole tank not just top bit. These often have switches on the side of tank to allow all or part heating of tank and are it seems a lot better than system used in rest of the UK.

And we say the Irish are Thick! Seems that's not true at least as far as plumbing goes.
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