High
S.11 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler is trying to heat your water, but the internal fan responsible for safety cannot get started.

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

DHW mode fan start up error

From this model's manual
Verified against the Vaillant Ecotec Combi installation & service manual, page 43.
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 control board sends a signal to the fan to begin spinning, but the fan fails to respond or reach the required speed. The most common reasons are a physical blockage in the fan's blades, a loose internal electrical connection, or a failure in the fan's motor and electronics.

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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