Radiator Valve Stuck Open Or Shut

What's happening?

A thermostatic radiator valve, or TRV, has a head that senses room temperature and a small spring-loaded pin in the valve body underneath that opens and closes the water. After a summer of not being used, or from limescale and rust, the pin can seize. Stuck down, it holds the valve shut and the radiator stays cold. Stuck up, it holds the valve open and the radiator stays hot however you set the dial. The head itself can also fail, with the wax inside no longer moving. The other valve on a radiator, the lockshield, has no head and is turned with a key or spanner. If it will not turn it has seized in the same way. A quick test with the head off tells you which part has failed, and replacing a head does not need the system drained.

What usually causes it?

• A seized pin in the valve body after months of not moving
• Limescale or rust on the pin or its seal
• A thermostatic head whose wax element has failed
• A valve that has been painted over or has a stiff spindle
• A lockshield or manual valve seized in position
• A worn valve body that no longer seats properly

Is it dangerous?

No. The pipework can be hot, so use a cloth and keep the heating off while you work.

Can I fix it myself?

With the heating off, unscrew the thermostatic head by hand or with a small wrench and lift it off. Look at the pin in the centre of the valve. It should spring back when pressed. If it is stuck, press and release it several times, and tap the side gently with a small spanner. A drop of penetrating oil on the pin can help. If it frees, refit the head. If the pin is fine, the head has failed, and a new one costs little and screws on. If the valve body is seized, it needs draining and replacing.

When should you call a heating engineer?

Call a heating engineer if the pin will not free, if the valve leaks when you work it, if the lockshield will not turn, or if you would rather not drain the system. Replacing a valve body means isolating and draining part of the heating.

What will the heating engineer actually do?

• Test the head and pin and free or replace them
• Isolate and drain the radiator or system to replace the valve body
• Refit new valves matched to the radiator and pipework
• Refill, vent and balance the radiator and check for leaks hot
• Check other valves of the same age and recommend replacement where they are stiff

Who fixes this

• Heating not working
• Thermostat and heating controls

Questions people ask

Sources & References

1. Vaillant: heating controls
2. Vaillant: most common boiler problems
3. GOV.UK: Approved Document L, conservation of fuel and power