High Lockout
F.65 on Vaillant Turbomax Plus 828

Your boiler's internal computer is overheating, which has caused the system to shut down to prevent damage to the electronics.

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

PCB processor temperature too high | Check earth connection or electronics defect

What causes this fault?

This fault occurs when the boiler's internal control center exceeds its safe operating temperature and shuts down to prevent the circuit board from melting or catching fire. It is usually caused by an electrical component failing on the board itself or excessive heat building up inside the boiler casing due to poor ventilation. In some cases, external heat source interference or a maturing electronic component can cause this overheating.

This fault is more common during the summer months or during heatwaves, as high ambient temperatures make it harder for the internal electronics to shed heat.

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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