Boiler not firing due to condensate pipe blockage
⚠️ Do NOT pour boiling water directly onto plastic condensate pipework — it can crack. Use warm water only.
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Most likely cause & what to check
All modern UK condensing boilers produce condensate — slightly acidic water — which drains through a plastic pipe (usually 21.5mm white waste pipe) to an outside drain or internal waste pipe.
In cold weather, this pipe can freeze where it runs externally, causing the boiler to lock out with a fault code (Worcester F1/EA, Vaillant F.28/F.29, Baxi E168 are common condensate codes — check our fault code tool).
Locate the condensate pipe outside the property — it is the white plastic pipe running from the boiler through an external wall, often ending near a drain.
Pour warm (not boiling) water slowly along the length of the frozen section. You may need to repeat this two or three times.
Once thawed, press the reset button on the boiler (hold 3–5 seconds). The boiler should fire normally.
To prevent a recurrence, insulate the exposed section of condensate pipe with foam lagging (available from any plumbers' merchant for under £5).
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