5 pulses (No light) Low

Worcester Bosch 5 pulses (No light) Fault Code

Also written as 5PULSESNOLIGHT — same fault.

The Worcester Bosch 5 pulses (No light) fault code means: your boiler isn't broken; it has simply been left in a manual 'test mode' used by engineers, and needs to be switched back to its normal setting.. It appears on 5 Worcester Bosch models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Not a fault code. Service mode selected to max, press service button to return to normal.

What causes the Worcester Bosch 5 pulses (No light) fault?

This occurs because the 'service' button on the control panel was pressed, which puts the boiler into a manual testing mode. This is usually done by an engineer during a service to force the burner to its maximum output, and the flashing light is simply a status indicator showing the mode is active. It is not an internal component failure, but rather a functional setting that hasn't been switched back to normal operations.

DIY fix possible

Locate the 'Service' button (usually marked with a spanner icon).Press and hold the Service button for a few seconds until the light stops pulsing.The boiler should return to its normal operating mode automatically.

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Worcester Bosch models that show the 5 pulses (No light) fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch 5 pulses (No light) fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026