F.77
FAULT CODE
Vaillant
Flue Non-Return Flap / Condensate Pump Error
Medium Severity
Engineer Required
The condensate pump or flue non-return flap is not operating correctly. More common on boilers with a condensate pump rather than gravity drain.
Cold Weather Note
In winter, check that the condensate drain isn't frozen before investigating further.
Step-by-Step Fix Guide
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Step 1
Check the condensate pump (if fitted) is receiving power
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Step 2 Engineer only
A Gas Safe engineer should inspect the condensate system and flue non-return valve
Gas Safe Reminder
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.