How to fix a leaking radiator valve

Video by Plumberparts. This walk-through is based on the video "HOW TO REPAIR A LEAKING RADIATOR VALVE - Plumbing Tips" from Plumberparts, who cover the three main leak points — compression nut, TRV, and packing gland — in plain English. Worth watching before you pick up a spanner, especially the section on applying PTFE to an olive rather than just tightening the nut further.

1. Find exactly where the water is coming from

Before you touch anything, dry the valve and the surrounding pipework with a cloth and watch for a minute or two. Radiator valves have three common leak points: the compression nut at the bottom where the valve meets the pipe, the packing gland up in the valve body itself, and the threaded insert that connects the valve to the radiator. Each one needs a slightly different fix, so it pays to be sure which you are dealing with.

If the damp is around the lower nut, it is almost certainly the olive inside. If water is seeping from around the valve spindle — the bit the TRV head or manual cap sits on — that is the packing gland. A drip right where the valve threads into the radiator body points to the insert thread. Mark it with a dry tissue if you are struggling to see it clearly.

2. Gather what you need and turn the heating off

You will need a roll of PTFE tape, two adjustable spanners or a set of grips plus a spanner, a small bowl or some rags to catch water, and possibly a pair of pliers. That is genuinely it for most jobs. PTFE tape costs under a pound and solves the vast majority of radiator valve leaks in UK homes.

Turn the heating off and let the system cool down for half an hour. You do not need to drain anything — that is the good news. You will be isolating the individual radiator using its own valves, so the rest of the system stays untouched. Hot water under pressure is unpleasant; give it time to cool.

3. Isolate the radiator from both ends

Every radiator has two valves: the one you can see (usually the TRV or the manual wheelhead) and the lockshield valve at the opposite end, which is the plain-looking one under a cap. Close both of them. The TRV usually twists anti-clockwise to the closed position; the lockshield needs a small flat-bladed screwdriver turned clockwise.

Count the turns on the lockshield as you close it and note the number down. You will need to return it to exactly the same position when you finish, otherwise that radiator will not heat up properly once the system is running again. A quick note on the air bleed screw at the top of the radiator — keep that closed throughout.

4. Fix a leaking compression nut with PTFE on the olive

Hold the valve body steady with one spanner and use the other to slacken the compression nut — anti-clockwise, a turn or two, just enough to see the olive underneath. Do not remove the nut fully; a little water will weep out but it should be manageable with a rag underneath. Wrap several layers of PTFE tape around the olive, going in the direction you would wind it if you were tightening the nut. Retighten, check for drips, and that is usually that.

Do not just crank the nut tighter without PTFE first. Over-tightening compresses the olive permanently and eventually splits it, which turns a minor weep into a proper leak. PTFE fills the gap; brute force does not.

5. Fix a leaking packing gland

If the leak is around the valve spindle, remove the TRV head or the manual cap. Underneath you will find a small gland nut — it looks like a small hexagonal collar sitting just above the valve body. Undo this nut completely and slide it up the spindle. Wind a generous amount of PTFE tape around the spindle itself, then replace the gland nut and tighten it back down. The PTFE compresses to form a new seal around the spindle.

This fix takes about five minutes and is satisfying when it works first time, which it usually does. If the gland nut is corroded solid and will not budge, that is when things get more involved — see the “When to call a handyman” note below.

6. Reopen the valves and check for leaks

Open the lockshield back to exactly the number of turns you noted, then open the TRV or wheelhead. Have your rag ready and watch the repair point carefully as the radiator fills. A tiny drip at first is common; it often stops as the joint tightens under pressure. Give it five minutes with the heating running before declaring victory.

If it is still weeping, a second wrap of PTFE is usually enough. If the leak shifts to a different point — such as the radiator insert thread — isolate again and wrap PTFE around that thread too, winding it in the direction of tightening. Most radiators in East Kent homes are straightforward compression-fit jobs and respond well to this approach. Older systems with corroded fittings are a different matter.

When to call a handyman

Call Richard if the gland nut or compression nut is seized and will not shift without force, if PTFE has not stopped the weep after two attempts, or if the leak is from a cracked valve body rather than a joint. A valve that is visibly corroded or damaged needs replacing rather than patching, and swapping a radiator valve does mean draining that section of the system. If you are also getting cold spots on the radiator or the whole system seems to be losing pressure, it is worth getting someone in to look at the bigger picture rather than chasing individual drips.