How to Thaw a Frozen Condensate Pipe

What Is a Condensate Pipe?

Modern condensing boilers extract so much heat from the flue gases that the gases cool and condense into liquid water (condensate). This acidic liquid drains away through a plastic pipe — the condensate pipe — which usually exits through an outside wall or into an internal drain.

Why Does It Freeze?

In freezing temperatures, the section of condensate pipe that runs outside is vulnerable to ice forming inside it. When the pipe freezes, the condensate has nowhere to go and the boiler locks out — displaying a fault code and refusing to fire.

Common fault codes for a frozen condensate pipe:

How to Thaw a Frozen Condensate Pipe

Step 1: Identify the Frozen Section

The frozen section is almost always the external part of the pipe — usually a white or grey plastic pipe (CPVC or PVC) that exits through an outside wall. Feel along the pipe for the coldest section.

Step 2: Apply Warm Water

The safest and most effective method is to pour warm (not boiling) water from a watering can or jug over the frozen section. Start from the lowest point and work upward.

Do not use boiling water — it can crack the plastic pipe and cause more problems.

Step 3: Use a Wrapped Hot Water Bottle

Alternatively, wrap a hot water bottle around the frozen section and hold it in place. This is gentler and just as effective for milder freezes.

Step 4: Reset the Boiler

Once you've thawed the pipe, go back inside and reset the boiler using the reset button (refer to your boiler manual). The boiler should fire up normally.

Preventing It Happening Again

If you're unable to thaw the pipe or the boiler still won't restart, call Halo Heating. We cover emergency boiler breakdowns across West Sussex 24/7.