High Lockout
E2 on Worcester Bosch Greenstar 25 HE Combi

Your boiler has detected a problem with the internal sensor that monitors the temperature of the water heading to your radiators, causing the system to shut down for safety.

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

CH flow NTC sensor defective (short or open circuit)

What causes this fault?

This fault occurs when the electrical connection to the temperature sensor on the main heating pipe becomes unstable or fails completely. The most common reason is that the sensor itself has developed an internal electrical fault or the wiring has become loose or damaged over time, preventing the boiler from safely monitoring heat levels.

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

E9View →A1View →

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