High Lockout
E03 on Viessmann Vitodens 100-W

Your boiler has shut down because a safety sensor detected that the exhaust gases are too hot or are not escaping correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Burner does not start. Flue gas limiter has tripped. (Reset required: Turn control knob 'Reset' to the right until 'CL' appears, then turn back).

What causes this fault?

This fault occurs when a safety sensor detects that the gases produced by the burner are reaching dangerously high temperatures before they can exit the flue. The most common reasons are a build-up of debris or limescale inside the heat exchanger, which prevents heat from being transferred to your water, or a physical blockage within the flue pipe itself.

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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