"Lee" wrote
| Assuming the boiler thermostat isn't already up full of course,
| and the OP did say "increase the heater temperature" - which
| suggests it isn't

That would only make a difference if the boiler is cutting out whilst there
is still a demand for heat. That's possible with hot water only once the
cylinder reaches 50--70degC, but unlikely with heating as if the rooms are
still below 20deg and the radiator stats are open there should be ample
dumping of heat from the boiler to keep the boiler stat on even at low
settings.

Owain