High
F.01 on Vaillant Ecomax Condensing 600/800 series

Your boiler's internal sensor that monitors the temperature of water returning to the system has lost its connection or stopped working, causing the unit to shut down for safety.

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

Return-NTC open circuit

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.00View →

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