If this
is the thermostat, then is seems a common problem, I had it with mothers house is slowly reduced the range it would work away from base until in the end it was 2 foot away from base. Lucky is was a second thermostat and the other one continued to work.
We are told the thermostat should be in a room normally kept cool, so as summer comes it will turn off boiler earlier, on the lower floors as heat raises, in a room without outside doors, and with no alternative heating. I don't know your house, my where I have lived no such room, although last house was open plan so a single thermostat between the two rooms worked reasonably well.
However mother old house and this one, we have doors, OK old fashion idea, but many homes still have them, so we need multiple thermostats, what we normally use is TRV's (Thermostatic radiator valves) and in theroy no need for a wall thermostat, in practice however we like to adjust the home temperature through the day, having rooms cooler when we retire. And when the temperature is lowered without some central switch of some sort, the boiler would be cycling off/on/off all the time and wasting fuel.
So some wall thermostat is desirable to turn off boiler when temperature is reduced, but still allow it to fire up if the night is really cold.
Easy option is a thermostat linked to TRV heads, but a number of wall thermostats in key rooms all wired in parallel can do the same job.
We are told do not put a TRV on the radiator where the wall thermostat is, and if there is only one wall thermostat, and it is in a room as described earlier then yes, but most homes that room does not exist so we use the hall, which clearly has an outside door, so a TRV and wall thermostat is required, the TRV will open when the outside door is opened, then throttle back so other rooms have chance to also heat up before boiler turns off, which means the lock shield, TRV, and wall thermostat in the hall are crucial to be set correct if keeping rest of house warm.
However it is likely any other heated room could be used.
Faults in the settings can mean rooms not warm enough, I have this problem at the moment with my own home, and am experimenting with boiler output temperature, but rooms can't over heat, as the TRV's will limit the temperatures in each room as long as set correctly.
So you could put the wall thermostat next to base and have it run the boiler all the time, and no room will over heat, OK may use a little extra fuel, but it would work OK.
I will admit I do not set all my TRV's to turn down over night. These setting will not do much to reduce temperature over night,
however my programmable wall thermostat is still working, so at midnight the room will cool as main wall thermostat has turned down,
I have set it to 16 which is nearly the same as off, as unlikely to cool to 16 by 8 am. But I could set all the electronic TRV's to also cool down. I must admit the old types with *123456 are a bit hit and miss, as one has to guess what 20ºC is, normally between 2 and 3 so one wonders why they go to 6?
