312 Low

Main 312 Fault Code

The Main 312 fault code means: your boiler is currently running a self-cleaning process to remove trapped air from the system.. It appears on 1 Main model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: de-aeration is taking place

DIY fix possible

Wait for the process to complete, which typically takes a few minutes.Do not turn off or reset the boiler while this message is displayed.Once the display returns to normal, check your radiators for trapped air and bleed them if they are cold at the top.

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Main models that show the 312 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Main 312 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