I had to replace the thermostat on the immersion heater on the water water
tank at my parents' house recently as the thermostat decided that it didn't
wish to switch off anymore, continuously heating the hot water to very hot
levels.

The tank is a very old large one with an immersion heater mounted right at
the very top facing downwards. I replaced the thermostat like for like with
what was there before and now they have hot water without having to keep
turning it on and off at the switch!

The cap on the immersion heater cover claims the element is 27" in length,
but the thermostat that was already there was only 18" in length. Would this
be right, or should the thermostat not be 27" also? That is assuming that the
cap is correct and the element is actually 27" long... Don't know without
removing the whole element from the tank - not something I want to do as it's
actually working.

The problem is that although they now have hot water there is not much of it.
The system used to be heated by a gas boiler which has since been condemed!
That's why they since used the immersion heater as they have no desire to
replace the gas boiler (as it only heats the water). The problem is that with
gas heating (via coil inside tank) there was enough hot water for two baths,
now there is barely enough for one full bath.

Any suggestions? Would I be able to just change the thermostat to a longer
one, or would it not physically fit?

--
Dane Koekoek