High Lockout
F.49 on Vaillant ecoTEC Pro 28

Your boiler is struggling to send signals between its internal components because the communication line has a low electrical voltage.

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

Fault: eBUS - Undervoltage on the eBUS

What causes this fault?

This fault occurs when the boiler's internal communication system experiences a power drop that prevents components from 'talking' to each other. The most common reason is an electrical short circuit in the wiring or a failing electronic control board that can no longer maintain the correct voltage. It can also be triggered if external smart controls or thermostats are incorrectly wired into the boiler's data port.

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.27View →

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