BoilerFaultCodesWorcester Bosch C4273 Fault Code
The Worcester Bosch C4273 fault code means: your boiler has stopped working because the internal fan has been running non-stop for too long, causing the system to shut down for safety.. It appears on 3 Worcester Bosch models in our database.
Technical description: Continuous fan operation for the last 24 hours – appliance temporarily blocked
What causes the Worcester Bosch C4273 fault?
This fault occurs when the boiler's control system detects that the internal fan has been spinning continuously for a full 24-hour period without a break. This is usually caused by a communication error between the main circuit board and the fan, or a faulty component that is sending a constant 'on' signal even when heat isn't required. To prevent damage to the motor or overheating, the boiler safety software triggers a temporary shutdown.
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 C4273 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch C4273 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