Leave it off and wear an extra sweater.
to start with ...this
thermostatic valves should only be used to keep unwanted heat out of unsused rooms ie; bedrooms and spare rooms.
programmable room stats are the best option as they can give you warm periods when the home is occupied but are then set to prevent troughing of the temperature which as mentioned is inefficient.
keep all the internal doors shut when your heating is on as this can help prevent heat seepage to unwanted areas ie; up the stairwell.
if you have a foam lagged or unvented cylinder, set it to be on 'continuous as the effort to top up is far lower than to reheat plus the heating will work fasted due to no 'short circuit' in pipework.
get your boiler serviced, dirty boilers are inefficient and also unsafe. plus get the energy efficiency rating checked as i regularly see boilers that over 15 years (average lifespan) will cost over £10000 !!! more to run than a condensing boiler.
not supposed to be 'working' today