High Lockout
F.63 on Vaillant ecoTEC Pro 24

Your boiler’s internal computer chip has suffered a memory error, preventing it from processing the instructions needed to run your heating.

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: EEPROM - EEPROM faulty

What causes this fault?

This fault occurs when the boiler's main control board suffers a hardware failure, specifically within the chip that stores the permanent operating software. The most common reason is an electrical surge or age-related component wear that corrupts the internal memory, making it impossible for the boiler to perform its safety checks. Because the 'brain' of the appliance can no longer read its own instructions, it shuts down entirely to prevent unsafe operation.

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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