High Lockout
E2 on Worcester Bosch Greenstar 25Si

Your boiler's temperature sensor has failed or has a wiring issue, which means the system cannot safely monitor how hot the water is or provide heating and hot water.

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 thermistor short circuit or open circuit

What causes this fault?

This fault occurs when the internal sensor responsible for monitoring the temperature of the water leaving the boiler fails to send a clear signal to the main control board. The most common reason is that the sensor's internal electrical resistance has broken down over time, or the wiring connecting it has become loose or damaged. Because the boiler no longer knows how hot the water is, it shuts down as a safety precaution to prevent 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

E1View →E9View →EAView →

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