TRV electric/electronic heads, what will fit.

[ericmark]

I have fitted two heads in mothers house, they work, but not really that good, they are too clever. They do not switch on and off, but gradually open and close, with the idea that will reduce the hysteresis, however when the sun comes out the room can shoot from 18°C to 24°C within an hour, the bay windows catch the sun specially in winter and when that happens I want the valve to turn off, not just start slowly reducing the flow.

I see adverts for items like this

designed for underfloor heating, I wonder if these will fit a standard TRV? they look better than trying to install motorised valves and it would seem would control with a simple on/off, of course once a radiator is hot it will stay hot for some time, but with the heads I am now using even 6 hours latter the radiator is not cold, they are not hot the valve has closed but not completely. I am using the MiHome Energenie heads and in the bedroom with evening sun they are reasonable and keep the room within limits. But in living room we have either cool room when no sun has heated the room, or too hot where sun has come out.

Maybe I need to change the valve to match the head? But I don't fancy buying items just to see if they fit.