I needed a cover for my Tado radiator valves.
After a few attempts I've settled on 2 versions. One has vents on the top, you will be able to see the colour of the original valve showing through, but it also allows the temperature sensor to sample the air.
The second is a solid, intended for printing in vase mode. This will cover the valves in the same area as the wall mounted thermostat so it doesn't need access to clear air.
I've initially printed these in PETG, there's a chance they will melt if the radiators go above 80degC, but I think this is unlikely in the majority oif cases. If they don't stand up I'll look at dipping my toe into ABS or ASA printing.
Both are intended to be printed lid face down on the bed, no supports are required.