High Lockout
F.24 on Vaillant Turbomax Plus 828

Your boiler is heating up too quickly because the water isn't moving through the system properly, often caused by trapped air or a stuck pump.

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

Dry fire protection (temperature gradient of flow NTC too steep) | .Air in boiler/system, pump blocked or defective, pump output too low

What causes this fault?

This fault occurs when the boiler detects a sudden, sharp rise in temperature because the heated water isn't moving away from the burner quickly enough. The most common reasons are a lack of water pressure in the system, a pump that has seized up, or a physical blockage like sludge or debris preventing circulation.

This issue is more frequent in autumn when heating systems are turned back on after being idle all summer, which can cause the internal pump to stick.

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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