Most valves come as pairs the TRV and lock shield there are
instructions for the valve, which show it has the option of fitting pegs to restrict the range, but it does not seem to include the lock shield within the TRV, there are some where both are in the same head, but it does not seem this is one of that type, so other than ability to fit pegs same as any standard TRV.
So you the used have two controls, the TRV is as one may expect a thermostat so setting the numbers sets the temperature, the lock shield controls the flow, so it would seem likely the lock shield needs tweaking, however with the TRV on the return the lock shield valve setting is critical, if it is too far open the radiator will fill with hot water before the TRV can react to temperature change, that is why better if on the feed, so I set as follows.
1) Turn off completely.
2) ¼ turn at a time with 4 minutes between each turn open until you can feel some hot on feed pipes clearly while boiler is running.
3) Set temperature required.
4) Measure temperature of room, if over temperature close a little if under temperature open a bit.
Since I used MiHome Energenie heads the PC showed both target and current temperature, and in °C so easy enough to monitor using PC, phone or tablet until correct temperature was maintained, once the lock shield was set, for rooms not used as much I swapped the the heads for cheaper programmable heads or liquid filled heads and it continued to work fine.
In the main the bottom will stay cool with a modulating boiler, with a oil boiler that turns off/on the whole radiator may get hot, but whole idea of using a modulating set of controls is to stop the hysteresis, (over shooting temperature set) and supply the return with cool water so the boiler can extract the latent heat, the boiler output turns up/down not on/off, the TRV flow turns up/down not on/off, and if a wall thermostat is fitted it is connected to the ebus so again up/down not on/off except when used to stop cycling in the summer.
As summer returns the boiler will reach its limit and can't turn down any more, at that point it starts to cycle off/on, and it would continue to do that all summer unless manually turned off or some auto system turns it off, so often a on/off wall thermostat is fitted in a room on ground floor which is kept cool, has no outside door, and not alternative heating (or as close as possible to that) to turn off boiler as summer arrives, the wall thermostat normally set slightly higher than the TRV so in winter it does nothing.
There are other methods where the TRV is linked to wall thermostat, but giving the basic method.
