BoilerFaultCodesMain E109 Fault Code
The Main E109 fault code means: your boiler is struggling to move water around the system before it starts the heating process, which is often caused by a blockage or a pump issue.. It appears on 1 Main model in our database.
Technical description: Pre-circulation fault
What causes the Main E109 fault?
This fault occurs when the boiler detects that water isn't moving through the unit quickly enough during its initial startup checks. The most common reasons are a build-up of sludge blocking the internal pipework or a mechanical failure of the pump that circulates the water. Because the water can't flow, the boiler shuts down to prevent the heat exchanger from overheating.
This issue often surfaces in autumn when the heating is turned back on after a long summer break, which can cause internal pump components to seize up from inactivity.
DIY fix possible
Check that your boiler pressure is between 1.0 and 1.5 bar on the pressure gaugeEnsure all radiator valves and boiler isolation valves are fully openGently bleed your radiators to remove any trapped air pockets
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Gas Safe Register →Main models that show the E109 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main E109 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