Ideal elan 2 wall thermostat missing/can't find it

How long is a piece of string?

i) the previous owners had a wireless room thermostat and took the sender with them when they moved.

ii) The thermostat has not been installed in an obvious place. When friends moved into a house the thermostat had been mounted next to the boiler hence was controlling the temperature of the small room in which the boiler was installed.

iii) The previous owners/tenants relied on the TVRs to control the temperature in all rooms. (probably not very satisfactorily).

IMO, the better place to fit a thermostat is in the room where you spend most time sitting down watching TV etc. Often wired thermostats are sited in places where it was easiest to run the wires which these days can be rectified with a wireless thermostat.