If your Main boiler is showing E28, the current manufacturer error-code table describes it as a flue NTC sensor fault on the covered models. The sensor circuit may be open or short-circuited.
The definition applies to the appliance group that includes Main Eco Compact Combi and System boilers. Main has produced different ranges over time, so check the exact model before treating any online fault-code explanation as definitive.
What does Main boiler code E28 mean?
The boiler uses a temperature sensor to monitor conditions associated with the flue system. An NTC is a sensor whose electrical resistance changes with temperature. E28 means the controls have detected an electrical reading from that flue-sensor circuit that is outside the expected range.
The code identifies the circuit that needs investigation; it does not prove the sensor itself has failed. A connection, wiring issue or another control fault may produce the same display, and those possibilities need professional testing.
Which Main boilers use E28?
Baxi’s current reference includes E28 in the code group covering Main Eco Compact Combi and Main Eco Compact System appliances. Other Main boilers may use a different display or code set.
Find the full model name on the front panel, user guide or appliance label. Note any other symbols or codes on the display and take a photograph if the sequence changes.
Why does the boiler stop?
Temperature information connected with the flue is part of the boiler’s monitored operation. If the control cannot rely on the expected sensor signal, it may lock out rather than continue normally.
You may lose heating, hot water or both, depending on the boiler type and when the fault occurs. E28 alone cannot show whether the flue is blocked or whether combustion is unsafe; it reports the sensor-circuit fault defined by the manufacturer.
Safe checks before booking a repair
- Record the model and complete display. Include every letter, number and symbol.
- Check the outside flue terminal from a safe position. Do not climb, dismantle anything or insert an object. Simply tell the engineer if it is visibly obstructed or damaged.
- Check ordinary controls. Confirm that the thermostat or programmer is requesting heat.
- Check the pressure externally. Compare the gauge or display with the range in the model’s user guide.
- Use one reset only if the user guide permits it. If E28 returns, stop resetting and arrange a repair.
Do not remove the boiler casing, disconnect a sensor, inspect the internal flue path or test wiring. Work affecting a gas appliance and its flue must remain with a suitably qualified engineer.
Is E28 caused by cold weather?
Cold weather can expose other boiler problems, but the manufacturer defines E28 as a flue NTC sensor circuit fault. Do not assume the code is a frozen condensate pipe or try unrelated remedies unless your exact user guide shows a different message.
If a fault appears during freezing weather, record any additional code and any visible condition at the external terminal without touching it.
Can you keep resetting E28?
No. A single user reset may clear a temporary interruption if the manual allows it, but a code that remains or returns needs repair. Repeated resets do not fix an open or short circuit and may erase useful timing information.
If you smell gas, suspect carbon monoxide, see scorching, feel unwell or have a carbon-monoxide alarm sounding, stop normal troubleshooting and follow Gas Safe Register emergency advice immediately.
What will the engineer check?
The engineer will confirm the exact model and code meaning, review the fault history and test the flue-temperature sensor circuit in accordance with the manufacturer’s instructions. They may need to check the sensor, connections, wiring and control response, as well as confirm that the appliance and flue can operate safely.
The code is evidence, not a diagnosis of one replaceable part. Proper testing is what determines the repair.
Get your Main boiler working again
Book a fixed-price boiler repair so the E28 fault can be checked safely and put right.
Quick answer
On covered Main Eco Compact boilers, E28 means the flue NTC temperature-sensor circuit has reported an open- or short-circuit fault. Keep the casing closed, record the full display and model, and book a repair if one permitted reset does not clear it.