The Natural Philosopher wrote:

It doesn;t matter whethert tu re one degree or 100 degrees below TRV
temp, *thermostat temp. The rads and the boiler will be working full on.

That would only be true if the TRVs snapped shut in a binary fashion. In
practice these are analogue devices and close progressively as the set
temperature is approached, gradually throttling the water flow. If they are
all approaching the target temperature the boiler will modulate down due to
the reduced flow.

--
Mike Clarke