Just fitted a TRV (Drayton TRV4) to a radiator on a single pipe system, partly as an experiment (if it works, there are about another 6 to do).
However, it seems not to work. The flow restriction through it when fully open is too much resistance to get enough flow through the radiator, resulting in a hot area along the radiator top only. I might try moving the inlet to the top so the hydrostatic pressure difference between the hot and cooling water helps the flow, but I'm not hopeful this will make enough differemce to notice.
Just wondering if anyone has come across any suitable product for a single pipe system?