High
F.23 on Vaillant ecoTEC Pro 30

Your boiler has shut down because the water inside is not circulating properly, causing a significant temperature difference between the water leaving the boiler and the water returning to it.

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

Safety switch-off: Temperature difference too great (flow/return)

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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