BoilerFaultCodesWorcester Bosch 669 Fault Code
The Worcester Bosch 669 fault code means: your boiler has stopped working because it cannot safely clear waste gases through the flue pipe.. It appears on 1 Worcester Bosch model in our database.
Technical description: Differential fan pressure status
What causes the Worcester Bosch 669 fault?
This fault occurs when the boiler's internal safety sensors detect that the fan isn't moving enough air to safely vent exhaust gases outside. The most common reasons are a build-up of dirt or debris in the small plastic tubes inside the unit, or the fan motor itself failing after years of heavy use.
This issue is more common during the first cold snaps of autumn when a fan that has been idle over summer is suddenly required to run at high speeds.
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 669 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 669 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