Stop a radiator bleed valve leaking by tightening, resealing or replacing it, then bleed the system safely.
RBV-01Turn off the heating and let the radiator coolSwitch the heating off at the thermostat or boiler and wait at least an hour for the radiator to cool. Hot water under pressure can scald you. Lay a dust sheet or old towels on the floor under the valve to catch drips.
RBV-02Find exactly where the leak is coming fromDry the whole valve area with a cloth, then watch it closely for a few minutes. Check whether water is coming from the small square spindle in the centre, the seam where the valve screws into the radiator, or the vent hole itself. This tells you whether tightening, resealing or replacing the valve is the right fix.
RBV-03Try closing the valve fully firstFit a radiator key onto the square spindle and turn it clockwise until it stops, firmly but without forcing it. A lot of these leaks happen simply because the valve wasn't closed fully after bleeding air out. Dry the area again and check for a fresh leak after a few minutes.
RBV-04Drain a little water to drop the pressureIf it still leaks, hold a small bowl under the valve and open it slightly with the key to let a little water out, then close it again. Dropping the pressure this way makes it far less messy when you remove the valve in the next step.
RBV-05Remove the bleed valve and check the washerKeep the bowl under the fitting and unscrew the whole bleed valve out of the radiator body using an adjustable spanner. Look at the small rubber washer or seal inside it. If it's flattened, cracked, or missing, that's your leak.
RBV-06Reseal or replace the valveIf just the washer has failed, fit a new one of the same size. If the valve body or spindle is worn, corroded or the square has rounded off, buy a whole new bleed valve instead — they're cheap and more reliable than patching an old one. Wrap 2-3 turns of PTFE tape clockwise around the threaded end before refitting either part.
RBV-07Screw the valve back in and tightenThread the valve back into the radiator by hand first to avoid crossing the thread, then tighten it with the spanner until snug. Don't overtighten — the valve housing is soft metal and can crack. Wipe away any water left on the radiator.
RBV-08Bleed the radiator and check for leaksTurn the heating back on and let the radiator warm through. Hold a bowl under the valve, open it slightly with the key to let trapped air escape, and close it as soon as water flows out steadily with no more hissing. Check the valve again after 30 minutes and once more the next day.
RBV-09Tidy up and check system pressureMop up any spilled water and remove the dust sheet. If you have a combi boiler, check the pressure gauge — bleeding radiators often drops it, and you may need to top the system up using the filling loop as your boiler manual describes.
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