How to thaw a frozen condensate pipe

If your boiler stops working on a freezing morning, this is the first thing to check. It's often a ten-minute fix with a kettle.

Written by Jacob, founder of FindMeCover

Quick answer: Find the plastic condensate pipe where it leaves your home, pour warm (not boiling) water along it until it runs freely, then reset the boiler. Only do this where you can reach the pipe from the ground.

What is the condensate pipe?

Modern condensing boilers produce waste water as they run. It drains away through the condensate pipe, a plastic pipe, usually white or grey, that runs from the boiler to a drain. When part of it is outside, it can freeze in a cold snap. The water backs up and the boiler shuts down.

Signs it's frozen

How to thaw it

  1. Find the pipe. Follow it from the bottom of the boiler to where it goes outside. The frozen section is usually the coldest, most exposed part: a bend, a dip or the open end over the drain.
  2. Pour warm water along it. Use a watering can or jug of warm water. Not boiling: very hot water can crack the pipe. A hot water bottle or a warm cloth held against the pipe also works.
  3. Keep going until it runs freely. It may take a few goes.
  4. Reset the boiler as your user manual describes. It may take a few minutes to start working again.

Stay safe. Only thaw pipes you can reach from the ground. Don't climb a ladder in icy weather, and watch out for the water freezing on the path. If the pipe is high up, call an engineer.

Stopping it happening again

An engineer can insulate the outside section of the pipe, fit a wider pipe that's less likely to freeze, or reroute it so more of it runs inside. It's worth asking at your next service, before the next cold snap.

Never take the casing off your boiler or try to repair gas parts yourself. That work must be done by a Gas Safe registered engineer. With boiler cover, your provider sends one for you. Compare boiler cover.

Have boiler cover?

Call your provider before paying an engineer yourself. A repair like this is exactly what cover is for.

No cover yet? A new plan won't pay for a fault you already have, because problems that exist when you join aren't covered and there's a waiting period at the start. It can protect you next time.

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Last updated 30 October 2026