Quick summary: A radiator that never fully cools is usually caused by slow circulation or a valve that isn’t closing completely. It’s often harmless, but persistent warmth can point to inefficiencies in the system.
A radiator that stays slightly warm all the time is different from one that actively heats when the system is off. In many homes, it’s the result of residual heat moving slowly through the pipework.
Thermostatic valves are a common factor. Even when set low, a partially stuck valve can allow a trickle of hot water to pass through, keeping the radiator lukewarm rather than cold.
In older systems, gravity circulation can also play a role. Warm water naturally rises and can continue to move gently through certain sections of the system without the pump running.
This behaviour is often noticed alongside other balance-related issues, such as radiators losing heat quickly or inconsistent temperatures across rooms.
If the warmth is mild and stable, it’s usually not urgent. If it contributes to uneven heating or higher bills, adjusting flow or valve settings often improves things.
Understanding how heat moves around the system is part of the broader picture covered in this WarmGuide article.
