High Lockout
F.42 on Vaillant ecoMAX Pro 28E

Your boiler's main control board is struggling to identify which specific model it is due to an electrical communication error.

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

Short circuit on coding resistor

What causes this fault?

This fault occurs when the boiler's main control board loses the ability to read a small electronic component that tells it which model size it is managing. The most common reason is a signal failure caused by a short circuit in the wiring or a total failure of the main printed circuit board itself.

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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