When a condensing boiler stops during a hard frost, the condensate pipe has often frozen. To fix it, follow the plastic pipe from the boiler to where it leaves the house, find the frozen section (usually outside, at a bend or at the end), thaw it with warm water or a hot water bottle, then reset the boiler as described in its manual.
If the boiler still won’t start, or the pipe is somewhere you can’t reach safely, book a boiler repair. Don’t open the boiler casing.
Why the condensate pipe freezes
Condensing boilers produce acidic water as they recover heat from waste gases. It drains through a plastic pipe, often to an outside drain. In prolonged sub-zero weather, water in exposed sections freezes, blocking the pipe. The boiler detects the blockage and shuts down to protect itself.
How to tell it’s the condensate pipe
- The boiler stopped during freezing weather
- It’s gurgling or making a bubbling sound
- The display shows a fault code (your manual will list which code relates to this)
- The outside end of the pipe has ice at the tip
How to thaw it safely
- Trace the pipe from the boiler to the outside. Look for the lowest point, bends and the open end.
- Warm, not boiling. Use a hot water bottle, a warm cloth or a jug of warm water, at a temperature you could comfortably put your hand in. Boiling water can crack plastic pipe.
- Work along the pipe slowly, paying attention to bends and the end.
- Mind the ice. Poured water refreezes on paths, so take care. Don’t use ladders to reach high pipes; call an engineer instead.
- Reset the boiler following the manufacturer’s instructions. It may take a few minutes to fire up.
When to call an engineer
- The boiler won’t restart after thawing
- The pipe is at height or out of reach
- The pipe is cracked, split or disconnected
- There’s a different fault code
- It freezes again and again
Stopping it happening every winter
A condensate pipe that keeps freezing usually has a fixable installation issue. An engineer can:
- Increase the pipe size on external runs, which makes freezing less likely
- Insulate external sections with weatherproof lagging
- Reroute the pipe internally to a waste pipe, where possible
- Improve the fall and reduce bends so water drains quickly
- Fit trace heating in exposed locations
These changes can be made during a service or repair visit, or as part of a new boiler installation.
Cold snaps around Lincoln
Lincolnshire can see spells of hard frost in winter, particularly in open, exposed spots. Homes where the condensate pipe runs down an exposed or north-facing wall are the ones most likely to have problems when the temperature stays below zero for several days.
Frequently asked questions
Can I use a hairdryer to thaw the pipe?
Only if you can do it safely, well away from water, with the cable kept dry and using an outdoor-safe setup. Warm water or a hot water bottle is usually simpler and safer.
Is my boiler damaged if the condensate pipe freezes?
Usually not. The boiler shuts down to protect itself. Once the pipe is thawed and the boiler reset, it normally runs as usual.
How do I stop it freezing next winter?
Have an engineer check the pipe’s size, insulation and route. Small changes often solve the problem for good.
Need help getting your boiler going?
If your boiler won’t restart or the pipe keeps freezing, call us on 07717 224 048 or get in touch online and we’ll come out and sort it.