High Lockout
F.29 on Vaillant ecoMAX 635

Your boiler has lost its gas supply or the flame has gone out and it cannot restart itself.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Flame extinguished re–ignition unsuccessful | Cause: Gas supply absent or insufficient, Check flue duct

What causes this fault?

This fault occurs when the boiler is running but suddenly loses its flame and cannot successfully relight itself. The most common reasons are a temporary interruption in the gas supply, a blocked flue preventing proper airflow, or a build-up of carbon on the sensor that detects the flame.

This fault is more frequent during extreme cold spells, as external gas meters or regulators can freeze and restrict the flow of gas to the property.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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