High Lockout
A1 on Worcester Bosch 537i

Your boiler has detected that there is not enough water circulating inside it, which may prevent your heating and hot water from working 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 sensors detect that the pump is spinning without a sufficient flow of water. The most common reasons are a loss of system pressure, a build-up of air within the unit, or a mechanical failure of the pump motor itself.

This issue often appears in autumn when the heating is turned back on for the first time, as pumps can seize or trap air after sitting idle over the summer.

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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