Lockshield Valves and Balancing a Heating System
The lockshield valve, fitted at the other end of a radiator from the TRV, controls flow rate rather than temperature and is used to balance the whole heating system so every radiator gets its fair share of hot water.
The lockshield valve, fitted at the other end of a radiator from the TRV, controls flow rate rather than temperature and is used to balance the whole heating system so every radiator gets its fair share of hot water. It's rarely touched day to day, which is exactly why it's often overlooked when radiators heat unevenly.
What it does
A capped valve that's set once during balancing and left alone, restricting flow through radiators closest to the boiler so distant ones aren't starved.
How it fails
It seizes from lack of use, or its setting is knocked or reset during other work, throwing off the balance across the whole system.
Repair or replace
In most cases it's freed and correctly reset rather than replaced; only a genuinely damaged valve body needs swapping out.
Get your heating system balanced
Tell us which radiators heat fastest and which lag behind and we'll check whether the system needs rebalancing.
Questions we get asked
Is balancing something I can do myself?
It's possible with the right approach, but doing it accurately across a whole system usually needs the flow and return temperatures measured properly, which is why we recommend having it done professionally.
How often do lockshields need resetting after the first balance?
Not routinely — usually only after radiators are added, removed, or a valve has been disturbed.
Do I need a registered engineer to reset lockshields?
No, balancing radiators is a plumbing and heating task, not gas work.