High
F.23 on Vaillant Ecomax Condensing 600/800 series

Your boiler has detected that water is not circulating properly through the system, causing the water to get much hotter in one part of the pipe than another.

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

Water shortage (too large a temperature difference between flow and return NTCs)

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

F.22View →F.24View →

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