F.35
FAULT CODE
Vaillant
Flue/Air Supply Issue
High Severity
Engineer Required
A fault has been detected with the flue gas path or air supply. The boiler cannot safely vent combustion gases.
Cold Weather Note
In winter, ice and snow can block the external flue terminal. Carefully clear any obstruction without damaging the terminal.
Step-by-Step Fix Guide
-
Step 1
Check the external flue terminal for visible blockages such as snow, leaves or debris
-
Step 2
Ensure nothing has been placed in front of the flue outlet
-
Step 3 Engineer only
If the flue terminal is clear, call a Gas Safe engineer to inspect the internal flue components and air pressure switch
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.