Rooms below set temperature OK, clearly if boiler not running radiator can't heat up, but of the four rooms with Energenie MiHome TRV heads three often go over temperature. The odd one the hall, has an unbranded TRV from screwfix with the thermostat in the same room set to 18°C nine times out of ten shows 18°C. The rest are Honeywell VT15 bases and they don't go way over temperature but reporting 22°C when set at 20°C is common. Why is the question, some thoughts. 1) Valve base faulty. 2) Valve head faulty. 3) Installation head to base faulty 4) Needs lock shield valve adjusting. 5) Something else. What I wonder is if the TRV opens when boiler not running so when it it opens there is no response, it continues to open so once boiler does run it is wide open and before valve can shut radiator has heated up, when I removed a valve to fit new batteries I noted how quickly the radiator heated up, and they do take time to cool again. So could be just trimming lock shield valves is all that is required. Main thermostat in hall is a Honeywell Y6630D which is not ideal as it has anti hysteresis software built in, so starts using a mark/space regulation as target temperature is approached, however the kitchen thermostat is a Horstmann HRFS1 has no anti hysteresis but also no fail safe, so to fit a reliable thermostat without anti hysteresis means hard wiring which I really don't want to do. The two thermostats are in parallel the Horstmann gives a morning boost to keep boiler running longer so rooms have time to reach day time temperature. Hind sight and that is easy should have fitted EvoHome, however silly Bosch boiler will not work with OpenTherm so really on option but on/off thermostat. I simply may be expecting too much control from a TRV head? But worth asking to see if I have missed some easy adjustment, reasonably sure the heads are adjusted correct as when fitted as it closed you could hear valve strain slightly at end of travel, and some times radiators are cold when towel rails are hot so seems they can shut off completely, but often radiator warm (not hot) when target below actual.