Frozen condensate pipe: how to thaw it and stop it happening again
Your boiler stopped on a freezing morning? A frozen condensate pipe is one of the most common causes – and often one you can clear yourself.
Signs the condensate pipe has frozen
Modern condensing boilers make acidic water (condensate) while they run and drain it through a plastic pipe, usually white or grey. If part of that pipe runs outside, it can freeze in very cold weather. The water then backs up and the boiler shuts down to protect itself.
- The boiler stops working during freezing weather, often first thing in the morning.
- You hear a gurgling or bubbling noise from the boiler.
- The display shows a fault or lockout code. The code differs between makes – check your boiler manual.
- You can see ice at the open end of the pipe outside.
Thaw the pipe safely
Only do this if the frozen section is outside and you can reach it from the ground. Do not climb a ladder in icy weather.
- Find where the plastic pipe leaves the wall and follow it to the drain or open end. The blockage is usually at the end, at a bend or where the pipe is most exposed.
- Pour warm water (not boiling) slowly along the pipe, or hold a hot water bottle or warm heat pack on it. Repeat until the ice clears.
- Reset the boiler using the reset button, following the manufacturer’s instructions.
Never use boiling water, a kettle straight off the boil, a naked flame or a heat gun – they can crack or melt the pipe. Watch for ice where the water lands on paths. Do not remove the boiler casing.
If the boiler still won’t start
If the boiler does not restart after a couple of resets, shows a different fault, or the pipe freezes again and again, stop and arrange an engineer. Repeated resets do not fix the cause.
Stop it freezing again
The best fix depends on how the pipe is run. An engineer can:
- Insulate the outside section with weatherproof pipe lagging.
- Increase the outside section to a larger pipe – current installation guidance recommends at least 32mm outside – so it is much harder to block with ice.
- Shorten the outside run, or reroute the pipe to an inside drain such as a sink waste or soil stack where possible.
- Check the pipe falls steadily towards the drain so water does not sit in it.
Fixed-price work is confirmed after an assessment – from photos or a short video where possible, otherwise at a visit.
Arrange a visit
A diagnostic visit is £92.50 for the first 45 minutes of assessment. We explain the findings and the recommended next step, and confirm the price of any repair before work goes ahead.
Send your postcode, the boiler make and model, the fault code and photos of the pipe outside.