High Lockout
E01-840 on Worcester Bosch 24/28CDi II RSF

Your boiler has lost water pressure, and the internal component used to refill it is likely disconnected or faulty.

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

Charging Link Assembly

What causes this fault?

This fault occurs when the boiler detects that the system water pressure has dropped too low to operate safely. The specific error indicates that the internal mechanism used to refill the system is either physically disconnected, incorrectly inserted, or the sensor monitoring the water flow into the unit has failed. Essentially, the boiler cannot verify that it is being topped up with water, so it shuts down to prevent damage.

This issue often appears after the first cold spell of autumn when homeowners turn their heating back on and discover the system has naturally lost pressure over the summer months.

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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