How to Fix a Leaking Stopcock
Last updated: 7 September 2026
Tighten the gland nut, repack the packing, or replace the stopcock if the leak persists.
Overview
A leaking stopcock can waste water and cause damage to your property. This guide covers diagnosing and fixing a leaking stopcock.
Step-by-Step Fix
Before beginning any repair, ensure you have isolated power or water supplies. Clear your workspace, gather standard hand tools, and wear appropriate personal protective equipment (PPE).
- First, turn off the water supply to your property by using the external stopcock or the main supply valve to isolate the water before working on the internal stopcock. This is essential to prevent water from spraying out when you disassemble the valve and to allow you to work safely without the risk of flooding.
- Locate the leaking stopcock, which is typically found under the kitchen sink, in a utility cupboard, or near the front door. Identify where the leak is coming from - it may be from the spindle, the gland nut, or the body of the valve itself. This will determine which repair method is most appropriate.
- If the leak is from the spindle, carefully tighten the gland nut, which is the hexagonal nut around the spindle, using an adjustable spanner. Turn it clockwise a quarter turn at a time and check if the leak stops. Do not overtighten, as this can damage the spindle or make the tap difficult to operate.
- If tightening the gland nut does not work, you may need to repack the gland. Turn off the water supply, undo the gland nut, and remove the old packing material using a small screwdriver or pick. Replace it with new PTFE tape wound around the spindle in the direction of the thread, or use plumbers hemp with jointing compound.
- If the leak is from the body of the stopcock or if the valve is seized and cannot be operated, the entire stopcock needs to be replaced. This is a job for a qualified plumber as it requires draining the system and potentially dealing with the external supply. Do not attempt this repair yourself if you are not confident.
- When replacing the stopcock, the plumber will need to drain the system, cut out the old valve, and solder or compression-fit a new one in its place. This may involve working on the mains supply pipe, which requires specialist tools and knowledge of water regulations.
- After any repair, turn the water supply back on slowly and check for leaks around the stopcock. Operate the stopcock fully open and closed a few times to ensure it is working correctly. If you notice any drips or signs of leakage, tighten the gland nut slightly or call a plumber to inspect the work.
- If you are unsure about any step of this repair, or if the stopcock is in a difficult location, it is always safer to call a qualified plumber. A leaking stopcock can cause significant water damage if not repaired correctly.
Common Symptoms & Diagnostic Resolutions
Review the common error codes and operating symptoms below to quickly identify the root cause of the fault before ordering replacement parts.
| Symptom / Code | Likely Root Cause | Recommended Resolution |
|---|---|---|
| Leak from spindle | Worn gland packing or loose gland nut | Tighten the gland nut or repack the gland with new PTFE tape or plumbers hemp. This is a simple repair that most competent DIYers can handle with the water supply isolated. |
| Leak from body | Cracked or corroded valve body | The stopcock must be replaced. This is a job for a qualified plumber as it requires draining the system and working on the mains supply. Do not attempt to repair a cracked valve body with sealant, as this will not hold under pressure. |
| Stopcock seized and will not turn | Corrosion or mineral deposits have seized the spindle | Apply penetrating oil to the spindle and leave it for 30 minutes. Gently tap the valve body with a hammer to help free the spindle. If it still will not turn, call a plumber to replace the valve. Do not use excessive force, as this can damage the pipework. |
| Leak persists after repacking | The valve seat or internal components are worn | If the leak persists after repacking, the valve seat may be damaged or the internal components may be worn beyond repair. The stopcock will need to be replaced by a qualified plumber. |
Frequently Asked Questions
How do I know if my stopcock needs replacing?
If the stopcock is leaking from the body, if it is seized and will not turn, or if it does not fully shut off the water when closed, it needs to be replaced. A stopcock that is difficult to operate or does not seal properly is a risk in an emergency situation, as you may not be able to isolate the water supply quickly.
What is the difference between a stopcock and an isolation valve?
A stopcock is the main valve that controls the water supply to your entire property. It is usually located where the water main enters your home. An isolation valve is a smaller valve on individual pipe runs that isolates water to specific appliances or areas, such as a washing machine or a bathroom sink.
Can I replace a stopcock myself?
Replacing a stopcock requires draining the system and working on the mains water supply. This is not a job for a DIYer as it requires specialist tools and knowledge of water regulations. It is also notifiable under building regulations in some cases. You should always use a qualified plumber for this work.
How much does it cost to replace a stopcock?
The cost of replacing a stopcock varies depending on the location and accessibility of the valve. On average, you can expect to pay between £80 and £200 for a qualified plumber to replace a stopcock. If the valve is in a difficult location, or if the pipework needs to be modified, the cost may be higher.