The boiler temperature control...
Setting the control knob of the front of the boiler
I've come to notice that many people are perplexed about the function
of the temperature control knob on the front of their boiler, as it isn't clear what effect it
has. Hence this page to hopefully explain.
This control knob adjusts the temperature of the water coming from the
boiler. This water is used by the heating system controls for two different
Firstly, it is sent directly to the radiators when the central heating is ON,
so this is the temperature to which the radiators will heat. If you find your
radiators are scaldingly hot, turning this control on the front of the boiler to
a lower setting will reduce the temperature of the rads.
Secondly, this hot boiler water is used to heat the hot water cylinder. Here
it gets more complex. There is usually a thermostat attached to the side of the
hot water cylinder. This would normally be set to about 50 degrees C and is
designed to turn the boiler OFF when the cylinder reaches this temperature, in
order to save fuel.
The complexity arises from the fact that the boiler control needs to be set
to a higher value than the hot water cylinder thermostat, or the boiler water
will never raise the cylinder water to the setting on the cylinder thermostat.
Hopefully that makes sense! If the boiler temperature control is set too low,
the hot water cylinder thermostat will never be satisfied and will continuously
'call for heat' (as we say in the trade) so the boiler will continuously cycle
ON and OFF. This wastes fuel and heat so paradoxically, for economy it is better
to set the boiler temperature control higher than lower.
If you boiler seems to be for ever turning itself ON and OFF, try turning the
control to a higher setting (or the cylinder thermostat to a lower setting).
This may well fix the problem.
First created 18th April 2015
Last updated 23th April 2015