It turns out that you don't even need those for the case where the radiator is difficult to access, because you can get an unpowered remote TRV that works via (

It turns out that you don't even need those for the case where the radiator is difficult to access, because you can get an unpowered remote TRV that works via (it appears) some kind of heat pipe. Eg: https://www.screwfix.com/p/pegler-white-remote-adjustment-trv-head/8255v https://www.screwfix.com/p/pegler-white-remote-adjustment-tr...