How to Fix a Frozen Condensate Pipe
Last updated: 7 September 2026
Pour warm water over the pipe, use a hot water bottle to thaw it, and reset the boiler.
Overview
A frozen condensate pipe can cause your boiler to shut down. This guide covers safely thawing a frozen condensate pipe.
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, identify the condensate pipe, which is the white or grey plastic pipe that runs from your boiler to an outside drain or soakaway. It is usually 21.5mm or 32mm in diameter and often exits through an external wall. Once located, check whether the pipe is frozen by looking for ice or frost on the outside of the pipe or by feeling if the pipe is cold and hard.
- Do not pour boiling water directly onto the frozen condensate pipe, as this can cause the plastic to crack or soften. Instead, boil a kettle and mix the hot water with cold water in a bucket or watering can to achieve a warm, but not boiling, temperature. Alternatively, use a hot water bottle placed against the frozen section of the pipe to gently thaw it.
- Starting from the end of the pipe nearest to the outside wall and working towards the boiler, slowly pour the warm water over the frozen section of the pipe. Pour in a steady stream, allowing the warmth to gradually melt the ice blockage. Continue until you can see water flowing freely from the end of the pipe, which indicates the blockage has cleared.
- After the pipe has thawed, reset your boiler according to the manufacturer instructions. This usually involves pressing a reset button on the front panel or turning the boiler off and on again. If the boiler does not restart, wait a few minutes and try again, as the system may need time to refill with water.
- To prevent the condensate pipe from freezing again, insulate the entire length of the pipe that is exposed to the outside air using foam pipe insulation of the correct diameter. For a more permanent solution, consider having a condensate pipe trace heating system installed, which uses an electrical heating cable to keep the pipe warm.
- If the pipe is in a location that is particularly prone to freezing, consider having a qualified Gas Safe registered engineer reroute the pipe internally or increase the diameter of the pipe to reduce the risk of freezing. A larger diameter pipe is less likely to freeze because it has a greater volume of water flowing through it.
- If the condensate pipe repeatedly freezes despite your efforts, this may indicate a deeper issue with your boiler condensate drainage system. Contact a Gas Safe registered engineer to inspect the boiler and the drainage system to ensure there are no other contributing factors such as a blocked or incorrectly installed drain line.
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 |
|---|---|---|
| Boiler shows error code EA | Ignition failure often caused by frozen condensate pipe blocking the pressure switch | Thaw the condensate pipe and reset the boiler by pressing the reset button. If the boiler still shows EA after thawing, there may be a blockage in the condense trap or a faulty pressure switch. |
| Boiler error code E9 or E119 | Low system pressure, which can occur after a frozen condensate pipe is thawed | After thawing the pipe, check the boiler pressure gauge. If it is below 1 bar, use the filling loop to repressurise the system to 1.5 bar. If the pressure drops again quickly, there may be a leak in the system. |
| Condensate pipe has visible ice but boiler still running | The blockage is partial or the boiler has not yet sensed the blockage | Thaw the pipe immediately before the blockage becomes complete. A full blockage will cause the boiler to shut down and may trigger error codes that require manual resetting. |
| Water backing up from outside drain | The outside drain or soakaway is blocked, causing water to back up into the condensate pipe | Clear the outside drain by removing any debris or ice from the drain opening. If the drain is blocked with debris, use a drain rod or high-pressure water jet to clear it. |
Frequently Asked Questions
How do I know if my condensate pipe is frozen?
The most obvious sign is that your boiler has shut down with an error code such as EA, E9, or a generic fault indication. You can also check the condensate pipe by feeling it for ice or frost. It will feel cold and hard, and you will not be able to hear water flowing through it when the boiler is operating.
Can I prevent my condensate pipe from freezing?
Yes, the most effective method is to insulate the entire external section of the pipe with foam pipe lagging. For extreme conditions, consider having a trace heating system installed by a Gas Safe registered engineer. Another method is to reroute the pipe internally or install a larger diameter pipe.
Is it safe to use a hairdryer to thaw a frozen condensate pipe?
Yes, a hairdryer can be used on a low heat setting, but be careful not to overheat the plastic pipe as this can cause it to soften or distort. Never use a blowtorch, heat gun, or any open flame to thaw a condensate pipe.
How much does it cost to have a condensate pipe rerouted internally?
The cost of rerouting a condensate pipe internally depends on the distance and accessibility of the new route. Typically, this work costs between 100 and 300 pounds, but can be more if the new route requires significant changes to the boiler installation. This work must be carried out by a Gas Safe registered engineer.