High Lockout
E2 on Worcester Bosch Greenstar 25HE

Your boiler's internal thermometer that monitors water temperature has stopped working correctly, 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 or incorrectly fitted

What causes this fault?

This fault occurs when the sensor responsible for measuring the temperature of the water leaving the boiler fails to send a reliable signal to the main control board. The most common reason is that the internal components of the sensor have degraded over time, or the electrical connection has become loose or corroded. Because the boiler no longer knows how hot the water is, it shuts down to prevent the unit from overheating.

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 →EAView →

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