BoilerFaultCodesWorcester Bosch Fast Flashing Fault Code
Also written as FASTFLASHING — same fault.
The Worcester Bosch Fast Flashing fault code means: your boiler has detected an internal computer error that prevents it from starting, meaning you currently have no heating or hot water.. It appears on 2 Worcester Bosch models in our database.
Technical description: Internal fault Replace control board
What causes the Worcester Bosch Fast Flashing fault?
This fault occurs when the boiler's internal computer experiences a critical electronic failure, preventing it from processing signals or managing components safely. The most common reasons are age-related wear on the circuit board's capacitors or an electrical surge that has damaged the delicate microchips. Because the control board can no longer communicate with the rest of the boiler, the system shuts down immediately as a safety precaution.
This fault is occasionally more frequent during winter months due to increased electrical load on the system and a higher likelihood of power fluctuations during stormy weather.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Worcester Bosch models that show the Fast Flashing fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch Fast Flashing 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