High Lockout
1021 on Worcester Bosch Greenstar 8000 Life/Style

Your boiler is struggling to accurately measure the temperature of your hot water, which usually means your taps aren't getting hot enough or stay cold.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Cylinder charging or hot water temperature sensor faulty

What causes this fault?

This fault occurs when the boiler's internal computer stops receiving a reliable signal from the sensors that monitor your hot water temperature. The most common reason is that the sensor has either worn out internally or a connection in the wiring has become loose or corroded, preventing the boiler from knowing when to fire up to heat your water.

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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Related fault codes

1017View →

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