High Lockout
P3 on Worcester Bosch Greenstar 25 HE Combi

Your boiler's internal electrical circuit has lost power because a small safety fuse has blown, preventing the system from starting up.

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

Please wait, initialisation in progress. 24 V fuse blown. Replace fuse.

What causes this fault?

This fault occurs when an electrical surge or a short circuit within the boiler's internal components causes a small safety fuse to blow. The most common reason is a failing internal component, such as a sensor or the main pump, drawing too much power and triggering the fuse to protect the expensive control board. It acts like a household trip switch, cutting power instantly to prevent further electrical damage.

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

P1View →P2View →

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