F.36 flue gas recirculation; appliance shuts down shortly after ignition

Safety: This fault can indicate unsafe flue gas conditions. Do not operate the appliance until the cause is resolved by a qualified engineer.

• Check flue terminal location: Ensure the terminal is not too close to corners, windows, or other structures that can cause recirculation, as per Vaillant installation guidelines.
• Inspect for obstructions: Check for bird guards, nests, or debris blocking the terminal or flue.
• Examine flue joints and seals: Open the casing and inspect all flue connections for signs of leakage, staining, or damaged seals. Replace any compromised components.
• Room ventilation: Verify that the installation room has adequate ventilation and that extractor fans are not causing negative pressure.
• Combustion check: A combustion analysis should be performed to ensure correct operation after repairs.