The problem of room temperature set to 5°C can occur if you have a Homesmart multi-zone heating system fitted which uses Honeywell Evohome controls.

If you have turned off a smart TRV (thermostatic radiator valve) on your Honeywell Evohome system, then it will override the temperature you have set for the room it is in.  The target room temperature will then be set to the default minimum of 5°C.

So check the smart TRV in any room for which you are having trouble setting the temperature.