How to Fix a Frozen Boiler Condensate Pipe (Full Guide)

A frozen condensate pipe blocks the waste-water outlet from a modern boiler. This causes the unit to lock out or reduce heating efficiency. Clearing or preventing that ice build-up ensures your boiler runs safely, reliably and at full performance.

What is a condensate pipe?

A condensate pipe transfers 'condensate' or wastewater by-products, from a boiler to the outside of a property, usually depositing it in a sewage system.

Why does the condensate pipe freeze?

The outside piping of a boiler can be exposed to some seriously low temperatures which can cause the component to freeze, this could form a blockage and can lead to the boiler locking out (essentially shutting down) to prevent waste water from building up and flooding.

Signs of a frozen condensate pipe

Tell tale indicators of a frozen condensate pipe can include a boiler error code, bubbling or gurgling sounds being omitted from the unit/pipework, or general disruption of boiler function.

How to un-freeze a condensate pipe

The most common way to thaw out a frozen part of the condensate pipe, is to pour warm water over the outside of the piping, but be careful as not to cause a slip hazard. Also don't pour boiling water on the pipe, let this cool down for 10 minutes first, this will prevent possibly cracking the pipe and burning yourself

Alternatively, you can place a hot water bottle on the affected area or have the above ground part of the piping lagged (insulated).

How to fix a frozen condensate pipe (step by step)

While many modern combi boilers have integrated frost technology to combat cold weather issues, there are some other methods of prevention and ways to resolve these types of problems if they should occur.

Confirm symptoms - No heating/hot water. Boiler shows "lockout" or similar. Gurgling from outside pipe.
Find the condensate pipe - Usually a small white/grey plastic pipe on the outside wall, running to a drain.
Make it safe - Turn the boiler off at the controls. Wear gloves. Keep the area non-slip.
Thaw the pipe - Pour warm water along the outside of the pipe from top to bottom. Do not use boiling water, or hold a hot-water bottle against the frozen section.
Reset the boiler - When the ice clears, reset the boiler and check it fires normally.
If it refreezes or won’t reset - Call a Gas Safe engineer.

How to prevent a frozen condensate pipe (step by step)

Prefer an internal termination - Route to an internal foul drain wherever possible (BS 6798 principle).
Keep any external run short and with constant fall - Short as practical, correctly clipped, with continuous gradient to drain.
Increase pipe size externally - Use at least 30mm internal diameter when run outside.
Insulate correctly - Weatherproof, UV-resistant insulation. Guidance cites ≥13 mm on 32 mm pipe, and many installers use 19 mm O-class PVC-coated insulation for severe weather.
Consider trace heating on exposed runs - Fit trace heat cable plus insulation per manufacturer instructions.
Good fixings and falls - Clip approx every 0.5 m horizontal / 1.0 m vertical to maintain fall and prevent sags.

Quick fixes

Situation	What to do
Visible ice on pipe	Warm water over pipe or hot-water bottle, then reset
Pipe repeatedly refreezes	Arrange proper insulation or trace heating
External run is long/exposed	Re-route internally or upsize + insulate

We've since updated our original video with an updated on with a few extra steps to help prevent this next year.