BoilerFaultCodesWorcester Bosch Flash 4 times per second Fault Code
Also written as FLASH4TIMESPERSECOND — same fault.
The Worcester Bosch Flash 4 times per second fault code means: your boiler has detected an internal communication or airflow issue that has caused it to shut down for safety.. It appears on 1 Worcester Bosch model in our database.
Technical description: Code plug missing or failed. CH or DHW Sensor fault or out of position. Air pressure switch fault or condense in tubes. Fan fail or stiff. Blocked flue. Faulty harness. Board fault.
What causes the Worcester Bosch Flash 4 times per second fault?
This fault occurs when the boiler's internal computer loses communication with its key safety components or senses that air isn't moving through the system correctly. It often signifies that the fan cannot spin properly or the sensors responsible for monitoring heat and airflow have detected an unsafe operating condition. These sensors act as a safety net, shutting the system down to prevent damage or the release of exhaust gases into the home.
This issue is more frequent during periods of heavy rain or high humidity, as moisture can build up within the air pressure tubes and disrupt the signal required for the boiler to fire.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Worcester Bosch models that show the Flash 4 times per second fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch Flash 4 times per second 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