High Lockout
S.22 on Vaillant ecoTEC 65kW

Your boiler has detected a problem with the flow of water while trying to heat your taps, which usually means water isn't moving through the system 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

Hot water handling pump flow error

What causes this fault?

This fault occurs when the boiler's internal sensors detect that water isn't moving quickly enough through the system to safely transfer heat to your hot water. The most common reason is a blockage caused by limescale or debris in the heat exchanger, or a mechanical failure in the secondary pump that pushes the water around.

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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Related fault codes

S.20View →S.24View →

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