High Lockout
E2 on Worcester Bosch CDi Classic

Your boiler has detected a fault with the sensor that monitors the temperature of the water leaving the unit, preventing it from heating your home safely.

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

Central heating (CH) water flow negative thermistor coefficient (NTC) sensor defective check CH flow NTC sensor and connection leads.

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with the sensor that measures the heat of the water heading to your radiators. The most common reason is that the sensor has physically failed or developed a short circuit, though it can also be caused by loose or damaged wiring connecting the sensor to the main control board.

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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