How to Replace a Stopcock (UK DIY Guide)
A faulty stopcock can make it difficult to shut off your home’s water supply in an emergency. If the valve is seized, leaking or won’t fully close, replacing it can prevent serious water damage.
This step-by-step UK DIY guide explains how to replace a stopcock safely and when to call a professional.
Tools You’ll Need
- Adjustable spanner
- Pipe wrench
- Pipe cutter
- PTFE tape
- Bucket and towels
Materials Required
- New stopcock (correct pipe size)
- Compression fittings (if required)
- Replacement pipe section (if needed)
Step 1: Locate and Turn Off the External Water Supply
Before replacing the internal stopcock, you must shut off the external water supply.
This is usually located:
- In a pavement box outside the property
- Under a metal cover marked “Water”
Turn clockwise to shut off the mains supply.
Step 2: Drain the System
Open all cold taps in the property.
Flush toilets to remove remaining water.
Allow pipes to drain fully.
Place towels around the work area.
Step 3: Remove the Old Stopcock
Loosen the compression nuts on either side of the stopcock.
If soldered, you may need to cut the pipe carefully.
Remove the old valve.
Inspect pipe ends for damage.
Step 4: Install the New Stopcock
Wrap PTFE tape around threaded fittings.
Insert the new stopcock in the correct flow direction (arrow indicates flow).
Tighten compression nuts evenly.
Do not overtighten.
Step 5: Turn Water Back On
Slowly turn the external supply back on.
Close internal taps gradually.
Check all connections for leaks.
Test the new stopcock by turning it off and on.
Common Mistakes to Avoid
- Forgetting to shut off external mains
- Installing valve in wrong direction
- Overtightening compression fittings
- Failing to drain pipes fully
- Using incorrect pipe size
Stopcock replacement requires confidence and careful preparation.
When to Call a Professional
You should contact a plumber if:
- The external mains valve cannot be located
- Pipework is corroded or damaged
- Soldering is required
- The stopcock is in a difficult-to-access location
- Leaks persist after installation
See our Plumbing Repair Cost Guide for typical UK pricing.