Available in pairs, the first is the temperature control valve (automatic or manual) and the second is the lockshield valve, which is used to balance throughput of the hot water to the radiators across the entire central heating system.

Without these valves, radiators placed closest to the boiler would heat up faster than those further away, thereby making one room very hot and the others less cool the further they are away from the boiler.

Lockshield valves are more closed on radiators close to the boiler, and increasingly open as radiators are positioned further from the boiler.

These are added to each individual radiator to permit different temperatures around the home. A Thermostatic Radiator Valve (TRV) controls the room temperature by reading the current air temperature and appropriately opening or closing the inlet valve to the radiator to achieve the preset temperature.

This is distinct to a standard valve on a radiator which maintains the temperature of that radiator, regardless of the room temperature.