High Lockout
F.00 on Vaillant ecoMAX Pro 28E

Your boiler has stopped working because it can no longer accurately measure the temperature of the water leaving the unit.

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

Flow NTC open circuit

What causes this fault?

This fault occurs when the boiler's control board loses communication with the sensor that monitors the outgoing water temperature. The most common reason is that the sensor's internal electrical circuit has broken or its wiring has come loose, meaning the boiler can no longer operate safely without knowing how hot the water is.

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.01View →F.10View →F.11View →

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