Do this first
- Do not force it. A stopcock that has not moved in years is brittle, and the usual way a small weep becomes a flood is somebody wrenching the handle to test it.
- Find your outside stop valve before you touch the inside one. It is normally in a small covered chamber in the pavement or front path, and it needs a long key rather than a hand. Knowing where it is means you have a fallback if the internal one fails while you work.
- Get a container and a towel under it, and clear the cupboard out. Most internal stopcocks sit under a kitchen sink surrounded by things that should not get wet.
- Identify where the water is emerging. Dry the whole valve, then watch: the spindle under the handle, the gland nut behind it, the compression nuts at either side, or the body casting itself.
- If it is the gland, a quarter turn on the gland nut with a spanner often stops it. Snug, not forced.
- If the body is weeping, or there is green crust on the brass, stop and leave it alone. That valve is at the end of its life and needs replacing under controlled isolation, not tightening.
What is actually leaking, and what it means
The stopcock is the one valve you need in an emergency, and it is also the valve most likely to have seized in the twenty years since anyone last turned it. Three failures, three very different jobs.
| Symptom | Cause | Fix |
|---|---|---|
| Drip from under the handle, worse while turning it | Gland packing dried and shrunk | Tighten the gland nut, or repack it. Water can usually stay on. |
| Weep at a compression nut either side | Olive relaxed, or the pipe has moved | Remake the joint with the supply isolated outside |
| Water seeping from the casting, or a crusted green bloom | Dezincification of the brass body | Replacement valve. Do not tighten anything. |
| Handle turns freely but the water never stops | The washer or the seat has failed internally | Replacement, and you currently have no isolation point inside the house |
That last row is the one to take seriously even though nothing is dripping much. A stopcock that turns but does not shut means the next burst in the house has no off switch, and you will be waiting on the outside valve and a key you may not own. Replacing a tired stopcock is a short, planned job. Replacing it during a flood is not.
While you are there, check what the valve is made of. Older London houses often still have lead on the incoming side, and a stopcock joined into lead pipe needs a different approach from one on copper or MDPE. If yours sits on lead, our Thames Water hub covers the replacement question alongside the leak one.
What the repair involves
A gland repack is minutes and nothing gets turned off. A valve replacement means isolating at the external stop valve, draining the rising main down at the lowest draw-off, cutting the old valve out and fitting a new one with a drain-off point below it so the next job on the house is easier, then refilling slowly, venting the air out through the taps and checking every joint under full pressure.
Where the incoming pipe is lead, galvanised steel or perished plastic, we say so and price the options honestly rather than fitting a new valve onto a pipe that is going to fail next. Where the cupboard, floor or carpet has already been soaked, that gets dried and made good too. That is the scope of water leak repair, and the rate is on the pricing page.
When it is not us
- A quarter turn on the gland nut fixed it. Then it is fixed. Turn the valve fully open and closed twice a year afterwards to keep it free.
- The leak is at the outside stop valve chamber, or the chamber is full of water. That is the water company's apparatus up to the boundary. Report it to them rather than paying anyone to dig.
- You want a new valve fitted on a shared supply serving several flats. A shared pipe is the joint responsibility of the owners connected to it, so agree it before anyone isolates a building full of people.
- You rent. The supply installation is the landlord's to keep in repair, and this is a five-minute repair they should be arranging.
- Nothing is leaking and you only want it checked. Exercise it yourself, gently, twice a year. That is the whole of the maintenance.
- The work involves altering the incoming main. Certain water fittings work is notifiable to the water undertaker, and an approved plumber can issue a certificate of compliance for it.