Frozen condensate pipe? How to thaw it safely and get your heating back on

When temperatures drop below freezing, a frozen condensate pipe is the most common reason a modern boiler stops working. The good news: you can often fix it yourself in a few minutes.

Modern condensing boilers produce water as they work. It drains away through a plastic pipe called the condensate pipe, which often runs outside to a drain. In freezing weather, the water inside can freeze and block it. The water backs up, and the boiler shuts down to protect itself.

Signs your condensate pipe has frozen

• It’s below freezing outside and your boiler has suddenly stopped
• The boiler shows a fault or error code, or keeps locking out after you reset it
• You hear a gurgling sound coming from the boiler or the pipe
• The plastic pipe outside is cold and stiff, or you can see ice at the end of it

How to thaw it safely

• Find the pipe. Follow the white or grey plastic pipe from the bottom of your boiler to where it leaves the house. It usually freezes at the end, or at a bend outside.
• Warm it gently. Pour warm water – not boiling – slowly along the outside of the pipe, or hold a hot water bottle or heat pack against it. Boiling water can crack the pipe and scald you.
• Work along the pipe. Keep going until you hear the ice clear or water starts to drain.
• Reset your boiler. Once it’s thawed, press the reset button and follow your boiler manual. It may take a few minutes to fire up again.

When to call us

If you’ve thawed the pipe and the boiler still won’t work, or it keeps freezing every time the weather turns, get it looked at. Some condensate pipes are too long, too thin or run with too little fall outside, which makes them freeze more easily. An engineer can check the pipe run and recommend a longer-term fix, such as better insulation or a different route.

Our diagnostic visit is £78 inc VAT, and it comes off your bill if you go ahead with the repair on the day. BoilerJax members pay no call-out or diagnostic charges. More about boiler breakdowns and repairs.

How to stop it happening again

• Keep exposed condensate pipe outside insulated with weather-proof lagging
• On very cold nights, setting your heating to come on for short spells can help stop the pipe freezing
• Keep up with your annual boiler service, so the engineer can spot a vulnerable pipe before winter

Need a hand?

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