Radiator Still Cold After Bleeding
If a radiator is still cold after bleeding, air was not the cause — or there is a secondary problem preventing flow. The most common culprits are a stuck TRV (thermostatic radiator valve), a locked lockshield valve, or a system-wide sludge build-up.
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Most likely cause & what to check
Check whether the TRV (the valve with the numbered dial, usually on one side of the radiator) is open. Turn it to its maximum setting (usually 5). If it has been turned off or is jammed, this alone will stop the radiator heating.
Remove the TRV head (unscrew the cap) and check whether the pin underneath is stuck down. The pin should spring back up when you push it down. If it is stuck down, the TRV body is stuck closed — spray penetrating oil around the pin and work it up and down gently.
Check the lockshield valve on the opposite end of the radiator — this is the valve with a plastic cap (usually white). Remove the cap and use an adjustable spanner to open it by turning anti-clockwise. It should be open 1.5–3 turns for a balanced system.
Check whether the radiator is cold at the bottom as well as the top. Cold at the bottom indicates sludge (magnetite) settled in the radiator base — you can try flushing the radiator individually (disconnect it, take it outside and flush with a hose), or consider a full system power flush.
If all radiators in the house are cold except one, the problem is more likely a faulty pump or zone valve rather than the individual radiator — check for a seized pump or stuck zone valve.
If only the radiators upstairs are cold, check that the boiler pressure is at 1.5 bar — low pressure often affects upstairs radiators first as they are higher in the system.
If a single radiator is cold but others nearby are hot, balance the system by partially closing the lockshield valves on the hot radiators to push more flow to the cold one.
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