High
S.91 on Vaillant ecoTEC sustain

Your boiler is currently set to a 'showroom' mode which allows the display to work for demonstration purposes but prevents the burner from actually firing to provide heating or hot water.

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.

What the manual says

Manufacturer manual

Maintenance:Demomode

From this model's manual
Verified against the Vaillant Ecotec Sustain installation & service manual, page 50.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This fault occurs when the boiler's software is accidentally placed into 'Showroom Mode', which is a setting intended for shop displays only. It means the control board thinks it should only light up the screen for demonstration rather than actually igniting the gas to heat your home. This is usually caused by a technician forgetting to deactivate the setting during installation or a mistake within the service menu.

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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