The numbers on a thermostatic radiator valve refer to the temperature in the room, not the radiator.
The reason for a thermostatic radiator valve is that it can sense the temperature in the room and will let more or less hot water into the radiator accordingly.
If the room is cold, the TRV will allow more hot water into the room to heat it up. As the room gets warmer, the TRV will lower the amount of hot water coming into the radiator to maintain the temperature. If the room temperature starts to drop, the TRV will allow more hot water in.
Numbers & temperatures
The numbers on the valve correlate to the room temperatures below:
- 0 = Off
- * = 7°C
- 1 = 10°C
- 2 = 15°C
- 3 = 20°C
- 4 = 25°C
- 5 = 30°C
A fully functional TRV will detect the temperature of the room and automatically adjust the amount of hot water in the radiator accordingly.
The best way to use thermostatic radiator valves is to decide on comfortable room temperature and set the number on the TRV accordingly.