High Lockout
F.24 on Vaillant Turbomax Plus VUW 242E

Your boiler is struggling to move water around the system, often because the water level is too low or something is blocking the flow.

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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