Display shows F13 and unit will not enter regeneration when commanded

Safety first: No pressurized components need to be opened for this check.

• Check bypass position: Ensure the Viessmann bypass valve is in the service position. Some models inhibit regeneration when in bypass.
• Inspect cover switch: If your model has a cover safety switch, make sure the cover is properly closed and the switch is actuated.
• Verify programming lock: Enter the installer menu and check if a service lock or regeneration inhibit function is enabled. Disable it if appropriate.
• Test manual regeneration: Attempt to start a manual regeneration again. If F13 persists, the interlock circuit or control board may be faulty.
• Professional diagnosis: Have a technician test the interlock inputs on the Viessmann control board and replace components as needed.