What the condensate pipe is
Every modern condensing boiler produces a small amount of acidic waste water as it runs. That drains away through a plastic pipe, usually 21.5mm or 32mm, which very often runs out through the wall to an outside drain or gully.
When the temperature drops below freezing, water sitting in that external run can freeze solid. The boiler cannot drain, detects the blockage and shuts itself down to stay safe.
How to tell that is what it is
- It happens in cold weather, and usually first thing in the morning
- The boiler locks out and shows a fault code — commonly an EA, E1, F28 or similar depending on make
- You may hear a gurgling or bubbling from the boiler before it stops
- It has worked perfectly all summer
- There is a plastic pipe running out of the wall near the boiler to an outside drain
Thawing it safely
- Find the external plastic pipe. The frozen section is usually the exposed run, a bend, or where it meets the drain.
- Pour warm water along it — a kettle boiled and then left to stand for a few minutes, or hot water from the tap. Not boiling water. Boiling water can crack the plastic and, on a very cold day, can refreeze and make it worse.
- Work from the end nearest the drain back toward the house, giving it time to work through.
- Once it is running again, reset the boiler following your manual's instructions.
- If it does not restart after resetting, or it freezes again within days, stop and get an engineer out — the pipe run itself is the problem.
Stopping it happening again
Thawing it is the fix for this morning. The permanent fix is the pipe run, and it is worth sorting in autumn rather than in January.
- Insulating the external run with proper waterproof pipe lagging — not indoor foam, which soaks and freezes
- Increasing the diameter of the external section so it is far less likely to bridge with ice
- Re-routing it to terminate internally into a soil stack or waste pipe, which is what current guidance prefers where it is practical
- Shortening the external run and making sure it falls properly, with no sags where water can sit
Why this is such a North East problem
Nothing about the region is special except the weather and the housing. A lot of local boilers were fitted into properties where the shortest route out was through an exposed elevation, and an exposed run on a north or east-facing wall is exactly where ice forms first.
Common questions
Can I use boiling water on the condensate pipe?
No. Use warm or hot water, not boiling. Boiling water can crack the plastic pipe, and on a freezing day it can refreeze quickly and leave you worse off than you started.
Is it safe to keep resetting the boiler?
Resetting once after you have thawed the pipe is fine. Repeatedly resetting a boiler that keeps locking out without fixing the cause is not — the lockout is a safety function doing its job.
Will it freeze again next winter?
Almost certainly, unless the pipe run is changed. Lagging, a larger diameter or an internal termination are what actually fix it. Thawing only buys you the day.
Related guides
Why does my boiler keep losing pressure? What is actually included in a boiler service? Burst pipe: what to do in the first ten minutes
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