Radiator Valve Leaking Where The Spindle Is

What's happening?

A radiator valve has a spindle that moves in and out to open or close the water. Where the spindle passes through the valve body, a gland nut compresses a seal or packing so water stays in. Over years the packing wears, the nut works loose or the O-ring hardens, and water weeps out along the spindle, often showing when the valve is open and hot and stopping when it is closed. The drip is small, but it can run for weeks and cost the system pressure, and it sits right on the floor or carpet. A leak from the nut where the valve joins the radiator, the union, is a different thing from a spindle leak and has different fixes. Find where the water is first appearing, with kitchen paper held at each joint.

What usually causes it?

• A gland nut that has worked loose over time
• Worn or hardened packing or an O-ring under the gland
• Corrosion or limescale damaging the spindle surface
• A thermostatic valve body whose seal has failed
• A valve that has been over-tightened or knocked
• A nut at the radiator union, not the spindle, which is a separate leak

Is it dangerous?

Not directly, but the water is often hot and can damage floors, and repeated loss of pressure puts the boiler into lockout. Do not touch a hot valve.

Can I fix it myself?

With the radiator cold, take off the valve cap or head. You will see a gland nut. Tighten it by about a quarter turn with a suitable spanner and check for a drip. If it still weeps, undo the nut, wrap two or three turns of PTFE tape or a little valve packing round the spindle, and retighten. If the valve has no gland nut and is sealed by an O-ring, it needs replacing. Replacing a valve means draining the system or isolating and draining the radiator first.

When should you call a heating engineer?

Call a heating engineer if tightening does not stop it, if you cannot drain the system, if the drip is at the union or the body rather than the spindle, or if the system pressure drops each time. Call straight away if water is running rather than weeping.

What will the heating engineer actually do?

• Identify whether the leak is spindle, body or union
• Isolate and drain the radiator or system to the level needed
• Repack or replace the gland, O-ring or valve
• Refill, inhibit and vent, and recheck for leaks while hot
• Check other valves of the same age on the circuit

Who fixes this

• Heating not working

Questions people ask

Sources & References

1. Vaillant: why is my boiler losing pressure?
2. Vaillant: how to repressurise a boiler
3. Vaillant: heating controls