BoilerTroubleshooting2026-02-26
Blocked or Frozen Condensate Pipe
A blocked or frozen condensate pipe is a common winter cause of boiler lockout.
High-efficiency boilers drain condensate; a blocked or frozen pipe trips a lockout.
Why it blocks
In cold weather the external condensate pipe can freeze; debris or fat can also block it, backing up water and stopping the boiler.
The fix
Thaw a frozen pipe with warm (not boiling) water, then reset; insulating or rerouting prevents recurrence.
Key takeaways
- Common in cold snaps
- Thaw with warm, not boiling, water
- Reset the boiler after clearing
- Insulate to prevent refreezing
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