Symptoms
- One radiator stays cold while others heat normally
- Valves may feel stuck or unusually easy to turn with no effect
- Rest of the heating system works fine
Likely causes
- CommonClosed thermostatic or manual radiator valveA valve turned all the way down or closed will stop flow completely.
- CommonStuck or seized valve pinValves unused for a long time (like in summer) can seize in the closed position.
- PossibleTrapped air or sludge blocking flow entirelyA severe blockage can stop water from entering the radiator at all.
- PossibleClosed lockshield valve on the return sideThis valve is often overlooked since it doesn't have a visible dial.
What to do
- Check the radiator's control valve (usually with a numbered dial) is open, not turned to zero.
- Check the lockshield valve on the other end isn't fully closed; it should typically stay in a fixed, partly-open position.
- If a valve feels stuck, try gently working it back and forth rather than forcing it hard.
- Bleed the radiator to rule out trapped air as described for cold-top radiators.
- If the valve moves freely but the radiator still won't heat, sludge may be blocking flow and the radiator may need flushing.
- Call a technician if a valve is seized solid or if flushing doesn't restore heat.
Tools and parts
- Adjustable wrench
- Radiator bleed key
When to call a pro
Call a heating technician if a valve is seized or a flush doesn't restore heat to the radiator.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.