How to Fix a Leaking Boiler Pipe
Last updated: 30 September 2026
Turn off the boiler, identify the leak source, tighten the fitting, or replace the damaged section.
Overview
A leaking boiler pipe can cause water damage and lower system pressure. This guide covers diagnosing and fixing a leaking pipe near the 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. Allow the system to cool completely before working on any pipes. Place a bucket and towels under the leaking pipe to catch water.
- Dry the pipe and its fittings thoroughly with a cloth and observe exactly where the leak is coming from. Common leak points are compression fittings soldered joints and the pipe itself if it has been damaged.
- If the leak is from a compression fitting use an adjustable spanner to tighten the nut a quarter turn. Hold the fitting steady with a second spanner to prevent twisting the pipe. If the leak persists the olive inside the fitting may need replacing.
- To replace the olive turn off the water drain the pipe section and undo the compression fitting. Remove the old olive with a small hacksaw or olive puller. Fit a new olive and re tighten the fitting. Apply PTFE tape to the threads if necessary.
- If the leak is from a soldered joint the joint will need to be re soldered. This is a job for a qualified plumber or heating engineer as soldering requires skill and the correct tools. Do not attempt to repair a soldered joint with tape or sealant.
- If the pipe itself is cracked or damaged you will need to cut out the damaged section and replace it with a new length of pipe. Use a pipe cutter for clean cuts and connect the new section with compression fittings or soldered joints.
- Check the boiler pressure gauge after the repair. The pressure may have dropped when you drained the pipe. Repressurise the system to between one and one point five bar using the filling loop.
- Run the boiler and check the repaired pipe for leaks under pressure. Monitor for twenty four hours to ensure the repair has held. If the leak persists or you are unsure call a Gas Safe registered 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 compression fitting | Loose nut or worn olive | Tighten the nut a quarter turn. If the leak persists replace the olive and re tighten. |
| Leak from soldered joint | Failed solder joint or pinhole leak | The joint must be re soldered by a qualified plumber. Do not attempt to seal with tape or adhesive. |
| Leak from pipe itself | Cracked or corroded pipe | Cut out the damaged section and replace with new pipe and fittings. |
| Pressure drops after repair | System not fully refilled after draining | Repressurise the system using the filling loop to between one and one point five bar. |
Frequently Asked Questions
Why is my boiler pipe leaking?
Common causes include loose compression fittings worn olives failed soldered joints or corroded pipes. Corrosion often affects older pipework and requires replacing the damaged section.
Can I fix a leaking boiler pipe myself?
You can tighten compression fittings and replace olives yourself. Soldered joints require a qualified plumber. If the leak is from the boiler itself you need a Gas Safe registered engineer.
Does a leaking boiler pipe affect boiler pressure?
Yes water lost through a leak will reduce system pressure. After repairing the leak you will need to repressurise the system using the filling loop.
How much does it cost to fix a leaking boiler pipe?
Simple repairs such as tightening a fitting cost nothing if you do it yourself. Replacing a section of pipe costs twenty to fifty pounds for materials plus sixty to one hundred and twenty pounds for a plumber.