Yorkshire BELMONT III B1701/3 LIQUID HEAD 2M

A thermostatic radiator valve (TRV) controls the flow of hot water into a radiator according to the temperature of the room. A sensing head opens and closes the valve as the air warms and cools, so each room can be held at its own setting. TRVs are normally paired with a lockshield valve on the other end of the radiator, which the installer sets once to balance the system.

Body style and size

• Angled or straight: angled bodies suit pipes rising from the floor or coming out of the wall; straight bodies suit pipes that run in from the side.
• Pipe size: 15mm is standard; 10mm and 8mm suit microbore systems, sometimes with reducers.
• Connection: compression ends are the most common, with push-fit and drain-off versions also made.
• Flow direction: bi-directional valves can go on either the flow or the return pipe; others must go on the flow, so check the arrow on the body.

Heads

Standard heads use a numbered scale, usually from a frost setting up to 5. Wireless and smart heads add timed or app control. The M30 x 1.5 thread is widely used for heads, but some valve bodies use other connections, so check compatibility or use an adaptor.

Standards and regulations

Look for TRVs tested to BS EN 215. In England, when a boiler is installed or replaced, Approved Document L expects TRVs on every radiator except in the room with the main room thermostat. Keep heads clear of curtains and radiator covers so they sense the room temperature properly.

For valves without a thermostatic head, see manual radiator valves.