High Lockout
A1 on Worcester Bosch Greenstar 25HE

Your boiler is trying to work but cannot detect enough water moving through the system to operate safely.

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

pump has run dry

What causes this fault?

This fault occurs when the boiler's internal pump is spinning but is unable to move water through the heat exchanger. The most common reasons are a lack of water pressure in the system, a large pocket of air trapped inside the pump, or a physical failure of the pump motor itself.

This fault often appears in autumn when the heating is turned back on for the first time, as pump components can seize or become stuck during months of inactivity.

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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