BoilerFaultCodesMain E12 Fault Code
The Main E12 fault code means: your boiler has detected that water is not flowing properly through its internal system, so it has safely shut down to prevent overheating.. It appears on 2 Main models in our database.
Technical description: Circulation fault (primary)
DIY fix possible
Check that all your radiators are fully open and not turned off.Check your boiler pressure gauge to ensure it is between 1 and 1.5 bar.If the pressure is too low, top it up using the filling loop, then restart the boiler.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like E12: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Main models that show the E12 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main E12 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 31 August 2026