Frozen Condensate Pipe: How to Fix It and Prevent It

What is the condensate pipe?

All modern condensing boilers produce acidic water as a byproduct of burning gas efficiently. This water drains out through a small plastic pipe - the condensate pipe - usually into an outside drain or soil pipe. In freezing temperatures, the water in this pipe can freeze and block it.

How do I know it is frozen?

Your boiler will stop working and display an error code. Common codes for a blocked condensate include EA (Baxi), F28/F29 (Vaillant), and L2 (Ideal). You might also hear a gurgling noise from the boiler before it shuts down. If it is below zero outside and the boiler has suddenly stopped, this is the most likely cause.

How to thaw it yourself

Find where the condensate pipe exits the building - it is usually a white or grey plastic pipe about 22mm wide going into an outside drain. Pour warm (not boiling) water over the frozen section of the pipe. A hot water bottle or a warm cloth wrapped around the pipe also works. Once it thaws, reset the boiler. If it fires up, you are sorted.

How to prevent it freezing again

Lagging the external section of the condensate pipe with foam pipe insulation is the simplest fix. If the pipe runs a long distance outside, we can reroute it to a shorter run or increase the pipe diameter so it is less likely to freeze. Running the heating on a low setting overnight in very cold weather also helps keep the pipe warm. See our winter boiler preparation checklist for more tips.

When to call us

If you cannot find the condensate pipe, cannot thaw it, or the boiler does not restart after thawing, call us on 01932 943 009. We can thaw the pipe, check for any damage, and fit insulation to prevent it happening again.