How to Fix a Leaking Radiator Bleed Valve
Last updated: 30 September 2026
Turn off the heating, tighten the valve, replace the valve if damaged, and check the system pressure.
Overview
A leaking radiator bleed valve can drip water onto your floor and lower the pressure in your heating system. This guide covers diagnosing and fixing a leaking bleed valve.
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).
- Turn off your central heating and allow the radiator to cool completely. The water in the radiator can be extremely hot and will cause severe burns. Allow at least thirty minutes for the radiator to cool before you start work. Place a towel and a small container under the bleed valve to catch any water.
- Dry the bleed valve and the surrounding area thoroughly with a cloth. Observe exactly where the water is coming from. If the leak is from the bleed valve itself it may just need to be tightened. If the leak is from the spindle or the valve body it may need replacing.
- Use a radiator bleed key to gently tighten the bleed valve clockwise. Do not force it as overtightening can damage the valve seat and make the leak worse. Turn it a quarter turn at a time and check if the drip has stopped.
- If tightening does not stop the leak the bleed valve may be damaged or the valve seat may be worn. In this case the bleed valve needs to be replaced. Close both the thermostatic valve and the lockshield valve on the radiator to isolate it from the system.
- Place a container under the bleed valve and open the bleed valve fully to drain the radiator. This will take ten to twenty minutes depending on the size of the radiator. Once drained use a small spanner to unscrew the old bleed valve from the radiator. Note the thread size.
- Purchase a replacement bleed valve of the same thread size usually one eighth inch BSP. Apply a few wraps of PTFE tape clockwise around the threads of the new valve. Screw the new valve into the radiator by hand then tighten with a spanner a quarter turn past hand tight.
- Close the bleed valve fully. Open the lockshield and thermostatic valves to refill the radiator. Bleed the radiator to remove air then check the boiler pressure gauge and repressurise to between one and one point five bar using the filling loop if needed.
- Run the heating for twenty to thirty minutes and check the new bleed valve for any signs of leakage. If the leak persists the valve may have been overtightened or cross threaded. In this case remove and reinstall the valve carefully. If you are unsure call a qualified heating engineer.
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 bleed valve when closed | Worn valve seat or damaged internal seal | Tighten the valve gently. If the leak persists replace the bleed valve entirely with a new one of the same thread size. |
| Leak from around the valve body | Loose valve in the radiator or failed thread seal | Drain the radiator remove the valve apply new PTFE tape to the threads and reinstall. If the thread is stripped use a thread repair insert. |
| Drip when bleeding radiator | Valve opened too far or key not sealing correctly | Use a proper radiator bleed key and turn the valve anti clockwise only until air starts to escape. Close firmly once water appears. |
| Radiator will not refill after repair | Air lock or valve not fully open | Ensure the lockshield and thermostatic valves are fully open. Bleed the radiator again to release trapped air. |
Frequently Asked Questions
Can I replace a radiator bleed valve myself?
Yes replacing a bleed valve is a manageable DIY task. You need to isolate and drain the radiator remove the old valve and install a new one with PTFE tape. If you are unsure a plumber can do this quickly and cheaply.
What size is a radiator bleed valve?
Most radiator bleed valves use a standard one eighth inch BSP thread. Some older radiators may have different thread sizes so check before purchasing a replacement.
Why does my radiator bleed valve keep leaking?
The valve seat inside the bleed valve may be worn or damaged or the valve may be overtightened which deforms the internal seal. In most cases replacing the valve is the most reliable fix.
Do I need to drain the whole system to replace a bleed valve?
No you only need to drain the individual radiator. Close both valves on the radiator then open the bleed valve to drain just that radiator. This is a much smaller job than draining the whole system.