High
2 lights flashing fast on Worcester Bosch Greenstar Si

Your boiler has failed to ignite properly, meaning it cannot create the flame needed to heat your home or water.

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

FAIL POINT K

From this model's manual
Verified against the Worcester Bosch Greenstar 25si installation & service manual, page 32.
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 the boiler attempts to start but cannot detect a stable flame after several tries. It is usually caused by a lack of gas reaching the burner or a failure in the sparking system that triggers the ignition. In some cases, a faulty internal sensor may simply fail to recognize that the flame is actually lit, leading to a safety shutdown.

This fault is slightly more common in winter, as extremely cold temperatures can cause external gas regulators to freeze or internal components to fail under heavy demand.

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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Avoid the next call-out bill

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