Usually, the radiator at the highest point in the house cant be switched off s it allows the heat and air pockets to rise to the easiest bleed point?
Where is your boiler? Do you have a frost stat?
Firstly, as above, with a TRV system, one radiatior has to be always open (Usually bathroom towel rail, but depends on configuration of radiators and who installed the CH system) so that if the pump comes on, the water always has somewhere to go.
Secondly, If you have a frost stat and/or a boiler in an out building with a frost stat to protect it (Mine for example is in a lean to out building so has a frost stat because the outbuilding is not heated other than by the boiler)
Then the boiler will come on at random times, irrespective of the timer settings or even if you have switched the heating "Off" altogether, if it gets cold enough for the frost stat to kick in.
It has been sub zero in parts of the UK in recent nights (Even in S Wales I woke this morning to find thick ice on the car windscreen) Originally my frost stat was a bit over enthusiastic and cutting in about 55f which meant that the heating came on randomly during the night (Which was irritating cos it made the house too hot) but I have set it back now so it is no longer a problem ,
(I have only recently moved into house so not used to its systems yet)