Under floor heating stores energy, and uses with electric version a lot of power, and it has to have a double control, the floor temperature and the air temperature. The thermostats are very different to those used to control a boiler or motorised valve, the batteries in the standard two wire thermostat last about 2 years, because it is inconvenient when they go flat I change mine once a year,
a simple non programmable starts at around £20 an extra £4 and you can get the
programmable version cheap wired thermostats are OK, however if going for wireless learn from my error don't get the cheap type, as they don't fail safe, i.e. the central heating is stuck on.
Although you can get 7 day programmable where each day is independent they take a lot of setting, the 5 and 2 is cheaper and quicker to set, I used a Hosrtmann DRT2 thermostat in my house, daughter house and narrow boat and they have worked well for years, however seems no longer sold in the UK although still sold in Ireland seems the flomasta has replaced it as the cheapest programmable thermostat for boilers.
However there are three basic thermostats.
1) On/off at set temperature with normally around 0.5°C between on and off.
2) On/off where as it approaches set temperature it starts a mark/space ratio switching off and on with a smaller and smaller on time as it reaches the set temperature, this stops it over shooting, the
Honeywell Y6630D is a good example, looks like an old analogue thermostat, however it is a very good cleaver thermostat although not programmable.
3) The modulating thermostat, these connect to the eBUS of the boiler and turn the flame height up and down so if the boiler can use these then really no point in the other two types. Nest for example can be used both modulating and with mark/space ratio, as can EvoHome. Does need to match boiler OpenTherm is trying to be adopted as a universal system, but some major manufacturers like Bosch seems to be holding out and selling their own system instead.
As to if you even want a wall thermostat is another question, today there is a move to electronic TRV heads so each room is controlled independently, sounds good, but except for very expensive EvoHome you still need some thing to switch off the boiler as summer arrives, for the job of switching off boiler when summer comes, the cheapest of cheap thermostats can be argued do a better job than the expensive types.
What I found to my cost not all houses are the same, I fitted the DRT2 to my house with open plan rooms and it worked well, but in mothers house a single thermostat does not work, I found I needed two in parallel to switch boiler, and electronic TRV heads in the two main rooms, doors on the rooms and morning sun in bay windows resulted in a single wall thermostat not being suitable. Since you seem to have selected the wrong thermostat before swapping you need to consider the pros and cons of different methods of control, before getting a more suitable replacement.
