The difference between a wet patch and a ruined ceiling is usually about four minutes of hunting for a valve. Most people find out where their stopcock is on the worst possible evening, in the dark, with water coming through a light fitting.
This guide takes ten minutes to work through, and it is the single most useful maintenance job a householder can do. Do it now while nothing is wrong.
The internal stopcock: your main control
This is the valve that shuts off the mains water entering your house. In most local properties it is under the kitchen sink, but it is also commonly found in a downstairs cloakroom, a utility room, under the stairs, in a hall cupboard, or in older houses in a cellar or beneath a floor hatch near the front of the property.
Find it, then turn it. This is the part people skip, and it matters: brass stopcocks that have not moved in fifteen years seize solid or shear off in your hand. Turn it fully off, check a tap runs dry, then turn it fully on again and back a quarter turn so it does not stick. If it will not move, or it drips afterwards, have it replaced with a quarter-turn lever valve. That is a small job and it is the best money you will spend on your plumbing.
Every isolation point worth knowing
| Valve | Typical location | Isolates | Tool needed |
|---|---|---|---|
| Internal stopcock | Under kitchen sink or nearby | All mains water to the house | Hand |
| External stop valve | Small cover in path or pavement | Supply at the boundary | Stopcock key |
| Service valves | On the pipe at each tap, WC, appliance | One fitting | Flat screwdriver |
| Washing machine and dishwasher valves | Behind the appliance | That appliance | Hand or screwdriver |
| Radiator valves | Both ends of every radiator | That radiator | Hand and a spanner |
| Heating drain-off cock | Lowest point of the circuit | Heating water | Hose and spanner |
| Cylinder gate valve | Airing cupboard, cold feed | Hot water cylinder supply | Hand |
| Outside tap isolator | Inside, on the pipe to the tap | Garden tap | Screwdriver |
Service valves: the ones that save the drama
A service valve — a small in-line valve with a screwdriver slot — lets you isolate a single tap, WC or appliance without shutting the whole house down. Most modern installations have them; many older ones do not, or have them buried behind a cupboard base.
Locate the ones you have. If a WC fill valve is dripping or a tap needs a washer, turning a single service valve means the rest of the household is unaffected. If your property has none, ask for them to be fitted next time a plumber is in — it is cheap while the water is already off for other work.
The external stop valve
There is usually a second valve at the property boundary, under a small metal or plastic cover in the path, driveway or pavement. It needs a stopcock key, which costs a few pounds and is worth owning.
This valve is on the supply side and is generally Scottish Water's responsibility, but you can use it in an emergency if the internal stopcock has failed. Lift the cover, clear out the inevitable soil and leaves, and check you can reach the valve — doing that in daylight now is much easier than at midnight in the rain.
Heating water is separate
- The stopcock does not stop a heating leak. A sealed system holds its own water independently of the mains.
- To isolate a leaking radiator, close both valves: the thermostatic valve at one end and the lockshield at the other. Count and note the turns on the lockshield so it can be reset to keep the system balanced.
- To drain the heating circuit, connect a hose to the drain-off cock at the lowest point and open a bleed valve high in the system to let air in.
- Refilling a sealed system means using the filling loop and bringing pressure back to the correct cold figure, usually around 1 to 1.5 bar.
Make it usable by everyone in the house
- Label the stopcock clearly. A luggage tag on the pipe is enough.
- Take a photo of it and put it in a shared household album or note.
- Make sure every adult in the house, and anyone who house-sits, knows where it is.
- Keep a stopcock key, a flat screwdriver and an adjustable spanner somewhere obvious.
- For a holiday let or second home, put the location in the welcome pack and tell the key holder.
- Exercise the stopcock once a year — a spring maintenance task that takes thirty seconds.
While you are at it
Two other five-minute checks pay off. Look at your boiler pressure gauge and note the normal cold reading, so you can tell when it has dropped. And check the pipework in your loft and any outbuilding for gaps in the lagging, which is where the next burst will happen.
If you find seized valves, missing service valves or unlagged pipework, those are all small jobs individually and much cheaper than the flood they prevent.
Frequently asked questions
- Which way does a stopcock turn to shut off?
- Clockwise, the same as a tap. Turn it until it stops, then check a cold tap runs dry to confirm.
- My stopcock is stiff. Should I force it?
- No. Old brass stopcocks can shear. Try gentle back-and-forth movement, and if it does not free up, have it replaced with a lever valve rather than risking it in an emergency.
- I cannot find my stopcock anywhere.
- Check under the stairs, in a hall cupboard, under a floor hatch near the front wall, in a cellar, or in an external meter chamber. If you genuinely have none internally, that is worth putting right — we can fit one.
- Do I need to turn the boiler off when the water is off?
- For a combi, yes, since it should not fire without mains water. On a cylinder system, switch off the immersion heater as well if the cylinder may empty.
Seized stopcock or no isolation valves?
We fit lever stopcocks and service valves so you can isolate a single fitting instead of the whole house.