Lockshield valve

1 What it does

A radiator normally has a valve at each end. The one with the cap controls how much water can get through, and Viessmann says it cannot be easily altered and was probably set by the heating engineer so that water runs evenly through the system¹. The other end carries the control you turn, either manual or a thermostatic radiator valve¹.

Vaillant explains why flow needs setting at all. Location and connecting pipes affect how easily water reaches each radiator, and that can be adjusted through the balancing process³.

2 When to adjust it

The main reason is balancing radiators, which is where the makers' steps are set out. Viessmann also warns that this work is usually done by an engineer, because water leaks can occur when adjusting radiator valves².

A lockshield is not a daily control, and turning it will not act like a thermostat. Everyday settings belong on the valve at the other end¹.

3 Before you turn one

Vaillant's guide says the plastic cap has to come off before the valve can be adjusted³. It is worth noting how far you turn it, so you can get back to the setting. Vaillant gives that advice when radiators are worked on, telling readers to record valve positions so they can return to them⁴. Ideal says closing one probably takes somewhere between a quarter and half a turn⁵, though that describes a typical valve and is not a setting for yours.

4 Other radiator valve checks

Baxi group's Main Eco Compact manual tells users to open and close the radiator valves several times a year so they can still be rotated⁶. It does not say which valve it means, so it should not be read as advice to move a balanced lockshield. Worcester Bosch's advice to move valves every 2 to 3 months is specifically about thermostatic ones⁷.

If a radiator is completely cold, Vaillant suggests checking the valves are on the right setting. It says a valve can be blocked by sludge or limescale, and that a heating engineer is the best solution⁸. Worcester Bosch lists radiator valves among the places to check for leaks if pressure keeps dropping⁹.