Immersion overheat cut out

Don't by-pass it as it's a safety device, replace the element. Has it got a re-setting button on it? some have.

 

All current ones have an overheat cut-out, this was brought in several years ago when a child was scalded by an overheating and boiling cylinder sending boiling water through a bedroom ceiling as far as I remember.
(This is separate from the thermostat of course)

 

When doing EICRs on properties, you are encouraged to check immersions to ensure there is an overheat cutout in the immersion or stat. This is a request of many social housing groups etc.

If an overheat cutout is missing, it is common to replace the thermostat with one with a cutout. The one shot non resettable type being a preference of many housing groups.

IMO, if your fixed cutout has failed and you replace the thermostat with one which incorporates one, this is perfectly fine. It is what you would do if one wasn't present, so it's the same thing really.

 

It is all down to header tank used and if electric is only form of heating or not. With the one shot type cut out and electric only heating the heater tank can be thermal plastic but where for example solid fuel heating is used then the header tank has to be able to stand boiling water and the cut out has to be re-settable as the other form of water heating can trip the cut out.

In the 1950's we still had the cut out it was around 1980 when we started to get cheap imports without the cut out. http://news.bbc.co.uk/1/hi/england/somerset/7179092.stm shows the death of the baby it shows the failed tank however I lived in a house with solid fuel heating and the noise generated when the water boiled which happened a lot could not be missed. The report does not explain how they did not hear the noise and also of course had it been a metal tank or one of the special plastic ones designed for solid fuel it would not have burst. Also when ours boiled water was ejected onto the path outside how this was also missed I don't know.

Where the second form of water heating is gas then likely you could still use the one shot type cut out as unlikely the gas will overheat. As to solar I see no provision on my father-in-laws system to auto run off water if over heated so I would expect it's the same as solid fuel and the home owner is expected to manually run off water.