BoilerFaultCodesPotterton E109 Fault Code
The Potterton E109 fault code means: your boiler has detected that water is not circulating correctly before the burner lights, which usually means there is a blockage or a pump issue.. It appears on 2 Potterton models in our database.
Technical description: Pre-circulation fault
What causes the Potterton E109 fault?
This fault occurs when the boiler's internal sensors detect that water isn't moving through the unit quickly enough before the flames ignite. The most common reasons are a seized central heating pump that can't push the water around, or a build-up of sludge and debris creating a physical blockage in the heat exchanger.
This issue often appears at the start of autumn when the heating is turned back on after being idle all summer, which can cause the pump to stick.
DIY fix possible
Ensure your radiator valves are open to allow water flowCheck that the boiler pressure is between 1 and 1.5 bar on the gaugeRestart the boiler by pressing the reset button for five seconds
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Gas Safe Register →Potterton models that show the E109 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton E109 fault code information on this page is sourced and cross-checked against the official Potterton service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026