Roland Perry wrote:
Currently I have a boiler with a controller that simply turns it on (for
CH) during pre-programmed hours. Rads have thermostatic valves.

I'd like to add a room thermostat in the living room [running additional
wiring isn't an issue] but need to know if it can simply be put in
series with the timer-control.

AIUI traditional boiler wiring has the timer and thermostat operate (relay)
contacts in series to interrupt the mains to the boiler. So an additional
thermostat in series would turn the heating off when it has deemed it up to
temperature. It wouldn't allow a call for heat if an existing thermostat
or controller is open.

Theo