Thermostatic radiator valves (TRV) and manual radiator valves (MRV) are two types of fittings that are used to control water heating in radiators. TRVs are designed to automatically regulate the temperature in a room, while MRVs require you to manually adjust the temperature.
TRVs use a built-in thermostat to sense the temperature in the room and adjust the flow of hot water accordingly. This helps to ensure that the temperature in the room remains at a constant level and is not affected by external factors, such as opening a window or the sun shining through a window.
MRVs, on the other hand, require you to manually adjust the temperature in the room. This is done by turning the valve to the desired temperature and then manually monitoring the temperature in the room. This can be a bit more tedious than using a TRV, as you will need to adjust the valve frequently in order to maintain the desired temperature.
Overall, TRVs are more convenient and efficient than MRVs, and are therefore becoming increasingly popular in homes around the world. They provide a more consistent temperature in the room, while also helping to conserve energy.