BoilerFaultCodesWorcester 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 7 Worcester Bosch models in our database.
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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Gas Safe Register →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 27 April 2026