High
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.

What the manual says

Manufacturer manual

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

From this model's manual
Verified against the Worcester Bosch Greenstar 25 He Combi installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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