F.77 — Flue non-return flap/condensate pump fault

What does F.77 mean?

The boiler has detected a fault with either the flue non-return flap or the condensate pump. Both are vital for safe and efficient operation of the flue system.

• No response from the flue non-return flap.
• Condensate pump is defective.

Click steps to track your progress.

1. 1

   Press the fault clearance key on the boiler to reset it.

2. 2

   Check the condensate pipe for any visible blockages or freezing.

3. 3

   If the fault persists, contact Vaillant Service Solutions, as this involves internal flue components.