BoilerFaultCodesWorcester Bosch A6 Fault Code
The Worcester Bosch A6 fault code means: your boiler has lost communication with the safety sensor that prevents your underfloor heating system from getting too hot.. It appears on 1 Worcester Bosch model in our database.
Technical description: External under floor heating thermostat defective.
What causes the Worcester Bosch A6 fault?
This fault occurs when the link between the boiler and the safety sensor protecting your underfloor heating pipes is broken. The most common reason is a hardware failure in the external limit thermostat or a loose connection in the wiring that prevents the boiler from confirming the floor temperature is safe.
This fault is more common in autumn and winter when the underfloor heating is first switched on after being dormant for several months.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Search the official register for a qualified engineer in your area.
Gas Safe Register →Worcester Bosch models that show the A6 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch A6 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