On 08/11/2017 15:31, fred wrote:

Hot water, as heated by the central heating is ferociously hot, There
is some type of adjustable wired thermostat clipped on to one of the
pipes entering the hot water cylinder but fiddling with this has no
effect.

Is this a job for a plumber or an electrician ?

Probably a plumber - usually this tends to happen when a three way valve
sticks so that the hot water is always heated whenever the boiler is on.

An electrical thermostat failure more often produces cold "hot" water.

--
Regards,
Martin Brown