High Lockout
F42 on Ferroli BlueHelix Pro 32C

Your boiler has detected an unusual temperature difference between its sensors and has shut down to prevent any internal 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

Sensor control protection activation

What causes this fault?

This fault occurs when the boiler detects a conflicting temperature reading between its internal flow and return pipes. It usually happens because water isn't moving through the unit fast enough, or because one of the temperature sensors has become inaccurate or faulty. The boiler shuts down as a safety measure to prevent the heat exchanger from overheating due to this poor circulation.

This fault is more frequent in winter when heating systems are under high demand, as sludge or debris in the radiators can more easily restrict the water flow required for the boiler to operate safely.

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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