The internal thermostat on my Immersion Heater stopped working.
Due to the limited space, changing it would have been a problem, so I decided to use the Horsmann HCT2 Cylinder Thermostat rated at 16 amp in its place.
It works a treat and it is much easier to control different temperatures if required.
I most certainly recommend it.
It replaced a cheaper one from Screwfix and is a far superior product. The previous one had a very wide hysteresis between on and off, so wide that the water was only tepid before it turned on again. This stat is excellent and the water maintains a more constant temperature.