Boiler shows F29 after running briefly, then flame goes out

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Fluctuating gas pressure, partially blocked burner, condensate backing up into combustion chamber, faulty flame sensor

Safety: Do not ignore repeated flame loss; it can indicate combustion issues.

Check condensate drain: Ensure the Viessmann condensate trap and pipe are clear and not frozen or kinked.
Flue inspection: Verify the flue terminal is unobstructed and correctly fitted.
Gas supply stability: If other gas appliances also cut out, contact your gas supplier.
Technician service: A professional should clean the burner, check combustion with a flue gas analyser, and verify flame signal strength. Replace the ionisation electrode if weak.

Professional Required 5/5

Ionisation Electrode (Flame Sensor)

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