Pulsation on start Emergency

Worcester Bosch Pulsation on start Fault Code

Also written as PULSATIONONSTART — same fault.

The Worcester Bosch Pulsation on start fault code means: your boiler is struggling to ignite smoothly because the air and fuel mixture is incorrect or there is a blockage in the flue, causing it to shudder when it starts up.. It appears on 3 Worcester Bosch models in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: CF - Flue draught incorrect; Combustion settings incorrect; Faulty nozzle
Typical repair cost £150-350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Worcester Bosch models that show the Pulsation on start fault code

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

Source

Worcester Bosch Pulsation on start 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