High Lockout
Fault 52 124 on Worcester Bosch Greenstar CDi Compact

Your boiler has become confused because its internal temperature sensors appear to have been plugged into the wrong ports or are reading backwards.

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

Temperature sensors (T1 and T2) reversed.

What causes this fault?

This fault occurs when the boiler's control board detects that the temperature on the return pipe is higher than the flow pipe, which is physically impossible during normal operation. The most common reason is that the temperature sensors have been swapped during a recent repair or the internal wiring harness has developed a fault. In some cases, it can also be triggered by a significant blockage in the heat exchanger causing heat to back up.

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

EAView →E9View →

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