I have a Belux room thermostat on the system which has a Horstmann electronic timer controlling both hot water and heating seperately.
I have also tried a Potterton room thermostat which my local building provider recommended and hoped should do the trick. Unfortunately , it was no better than what I am currently using and still clicked in at 21 degrees. Yes , I also tried the electrical suppliers but no luck there either I'm afraid.
I really need is the name of a make/model of a room thermostat which actually works and will come on line at a low temperature but as you can see, I'm not having much luck in spite of my efforts to date.