BoilerFaultCodesMain 1 Red Flash Fault Code
Also written as 1REDFLASH — same fault.
The Main 1 Red Flash fault code means: your boiler is experiencing a temporary temperature reading issue and is currently trying to fix itself automatically.. It appears on 2 Main models in our database.
Technical description: Sensor error, sensor fault, temperature fault or flow fault – this is a temporary error, the system should reset on it’s own.
What causes the Main 1 Red Flash fault?
This fault occurs when the boiler's internal sensors detect a sudden or unusual temperature reading that doesn't match expected levels. It is usually caused by a 'hiccup' in the temperature sensor's communication with the main control board or a momentary restriction in water flow. Because it is often a temporary glitch, the boiler pauses briefly to see if the reading stabilises before trying to fire up again.
DIY fix possible
Wait 5-10 minutes to see if the boiler automatically resets itselfCheck that your radiators are bled and there is no trapped air in the systemEnsure your boiler pressure is between 1.0 and 1.5 bar on the pressure gauge
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Main models that show the 1 Red Flash fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main 1 Red Flash 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 7 July 2026