BoilerFaultCodesFerroli A42 Fault Code
The Ferroli A42 fault code means: your boiler has detected an unusual temperature difference between its sensors and has shut down to prevent any internal damage.. It appears on 7 Ferroli models in our database.
Technical description: Sensor control protection activation
What causes the Ferroli A42 fault?
This fault occurs when the boiler detects a conflicting temperature reading between its internal flow and return pipes. It usually happens because water isn't moving through the unit fast enough, or because one of the temperature sensors has become inaccurate or faulty. The boiler shuts down as a safety measure to prevent the heat exchanger from overheating due to this poor circulation.
This fault is more frequent in winter when heating systems are under high demand, as sludge or debris in the radiators can more easily restrict the water flow required for the boiler to operate safely.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Ferroli models that show the A42 fault code
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Source
Ferroli A42 fault code information on this page is sourced and cross-checked against the official Ferroli service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026