BoilerFaultCodesMain E28 Fault Code
The Main E28 fault code means: your boiler has detected a problem with the sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.. It appears on 5 Main models in our database.
Technical description: Flue negative thermistor coefficient (NTC) sensor error
What causes the Main E28 fault?
This fault occurs when the sensor responsible for monitoring the temperature of the exhaust gases sends an incorrect or missing signal to the boiler's control center. The most common reason is that the sensor itself has developed an electrical fault, though damaged wiring or a buildup of extreme heat in the flue system can also trigger the safety shutdown.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Main models that show the E28 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main E28 fault code information on this page is sourced and cross-checked against the official Main service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026