What
@SJSbuilding says is very true, with my system the bathroom radiator and the hot water tank have no valve to control them, and they are thermosyphon (gravity) so does not matter if pump running or not, the boiler will cool by heating them.
However my boiler is rather old and oil fired, with a modern gas boiler that can modulate, the temperature of the water is controlled by the return temperature, where with my old boiler it is controlled by the outlet temperature only. Modern boilers often have the by-pass valve inside the boiler.
So theory and remember theory does not always work in practice, but theory is the boiler sends out heated water, the TRV heads close gradually as the rooms get warm, forcing to start with more water around those radiators still open, and finally opening the by-pass valve, so slowly the return water temperature has a smaller and smaller difference to the outlet water, the boiler senses this and turns the flame height down (modulates) until it can't turn down any more, at which point it starts to cycle off/on (mark/space control) it times how long it takes for the return water to get hot, and adjusts the space between burns, so as weather improves the boiler fires up less and less (anti cycle software) however it can never shut down completely so a wall thermostat is often included so on warm days the boiler can turn completely off.
There is however a problem with TRV heads, they are slow, so if the lock shield valve is wide open, the radiator will get very hot, and continue to heat the room even when room has reached the target temperature, with the new electronic wifi TRV heads it is easy, we see
both target and current temperature, if current over shoots target then close the lock shield valve, and if current below target after it has had time to reach it, then open the lock shield valve. However with cheaper valves it only shows target,
so you need some other means to find out the current and you also have to consider that thermometer may not be exactly matched to the TRV head, so a little harder to set, some
do not even show the target temperature in °C, so we tend to set radiators with the same temperature drop incoming to outgoing throughout the house, and cross our fingers that the TRV head can control the radiator fast enough.
However some simply give up trying to set whole house room by room, and use the wall thermostat not to simply switch off system on a warm day, but control the whole house temperature like in the 1980's before the TRV become common, and before we had modulating boilers, the idea was the wall thermostat should be in coolest room on entrance floor with no outside doors, or alternative form of heating, and not to have a TRV in that room, the idea is the TRV heads stop other rooms over heating, and the room with thermostat on the wall controls the boiler, if such a room exists then that often works, however clearly the hall has an outside door, so if the hall is used, a TRV is still required, idea is when outside door is opened the TRV will also open re-heating the hall quickly, but before it reaches the wall thermostat temperature, it will start to close, so extending the time before wall thermostat turns off, so other rooms not starved of hot water.
Clearly a problem having TRV and wall thermostat in the same room, they need to match each other, so turning a wall thermostat up or down, means you also need to turn TRV up or down to match, I and I am sure most people have three temperatures through the day, over night around 18°C in morning around 19.5°C and in evening 20.5°C only way to do that is with a programmable TRV head, so both wall thermostat and TRV change temperature at the same time, however as standard we normally have wax or liquid heads which are not programmable, so we tend to not have a TRV on the radiator where the wall thermostat is.
Setting the lock shield is not easy, we can remove all TRV heads and set to say 5°C difference if we have a thermometer to measure it, but that is only a start point, if the TRV is on feed then not so bad, but if the TRV is on the return, the radiator can get hot before the TRV has chance to act, so it took me nearly a year of tweaking the lock shield valves in my mothers old house. In the end they did work, the target and the current temperatures matched, and when we sold the house and I put the old wax TRV heads back on and brought the electronic ones here, I found the old heads also worked A1, it was the lock shield setting which was critical, so since not touched the heating worked nearly as well using old wax TRV heads. Main problem was most were on the return.
This house does not have a modulating boiler, and so it is taking longer to set the lock shield valves, but at least there was a TRV in the hall, I did not need to fit one. Some TRV's have the lock shield valve built into them, you have to remove head to set lock shield, know they exist but never used them.
Point is pictures are great, so post pictures and then some one will help.
hope pics are ok both valves same 
