High Lockout
F.65 on Vaillant ecoMAX

Your boiler's internal control board has become too hot to operate safely and has shut down to prevent damage.

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

Electronics temperature too high

What causes this fault?

This fault occurs when the electronics inside the boiler reach a temperature that exceeds safe operating limits. It is usually caused by a hardware failure on the main circuit board or heat radiating from a faulty internal component that is causing the control box to overheat.

This fault is more common during the summer months or during heatwaves, as high ambient temperatures make it more difficult for the boiler's 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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