How to Fix a Boiler Leaking Water
Last updated: 30 September 2026
Turn off the boiler, identify the leak source, and call a Gas Safe engineer for internal leaks.
Overview
A boiler leaking water is a serious issue that can indicate pressure problems or failed components. This guide covers diagnosing and responding to a leaking boiler.
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 the boiler at the mains switch and turn off the water supply to the boiler at the isolation valve. Do not attempt to work on the internal components of a gas boiler yourself. Any work inside the boiler casing must be carried out by a Gas Safe registered engineer.
- Identify where the water is coming from. Common leak points on a boiler include the pressure relief valve the pump seals the pipe connections and the heat exchanger. Place a dry cloth or tissue around each area and observe where water appears.
- If the leak is from the pressure relief valve which is a small copper pipe that usually runs outside the system pressure may be too high. Check the pressure gauge and if it is above two point five bar bleed a radiator to reduce the pressure. If the valve continues to leak it may need replacing.
- If the leak is from a pipe connection tighten the compression fitting with an adjustable spanner. Do not overtighten as this can damage the olive and cause a worse leak. Place a cloth around the fitting to catch drips. If tightening does not help the olive or washer may need replacing.
- If the leak is from the pump seals the pump will need to be removed and the seals replaced. This is a job for a Gas Safe registered engineer as it involves working on the boiler internals and the sealed heating system.
- If the leak is from the heat exchanger this is a serious fault that usually means the boiler needs to be replaced. Heat exchangers are not economically repairable and can only be replaced by a qualified engineer. Contact a Gas Safe registered engineer immediately.
- While you wait for the engineer place towels or buckets under the leak to minimise water damage. Turn off the boiler and if the leak is significant turn off the water supply to the boiler entirely. Do not attempt to restart the boiler until it has been repaired.
- Once the engineer has repaired the boiler run the heating and check the boiler pressure. Top up the pressure if needed using the filling loop. Monitor the boiler over the next twenty four hours to ensure the leak has been fully resolved.
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 |
|---|---|---|
| Water dripping from pressure relief valve | System pressure too high or valve worn | Check the pressure gauge and bleed a radiator to reduce pressure. If the valve continues to leak replace the pressure relief valve. |
| Leak from pump area | Worn pump seals | The pump seals need replacing. This is a job for a Gas Safe registered engineer. |
| Leak from pipe connection | Loose compression fitting or worn olive | Tighten the fitting carefully. If the leak persists replace the olive and re tighten. |
| Leak from heat exchanger | Internal corrosion or failure | The boiler likely needs replacing. Contact a Gas Safe registered engineer to assess. |
Frequently Asked Questions
Is a leaking boiler dangerous?
A leaking boiler can be dangerous if the water comes into contact with electrical components. It can also indicate a serious internal fault. Turn off the boiler and call a Gas Safe registered engineer immediately.
Can I fix a boiler leak myself?
You can tighten external pipe connections and check the pressure. Any work inside the boiler casing must be done by a Gas Safe registered engineer. Do not attempt to open the boiler yourself.
Why is my boiler leaking water from the bottom?
Common causes include a faulty pressure relief valve worn pump seals a loose pipe connection or a failed heat exchanger. The exact cause determines the fix and the cost.
How much does it cost to fix a leaking boiler?
Simple repairs such as tightening a connection may cost eighty to one hundred and fifty pounds. Replacing a pressure relief valve or pump seals costs one hundred and fifty to three hundred and fifty pounds. A heat exchanger failure often means replacing the boiler entirely.