BoilerFaultCodesPotterton E18 Fault Code
The Potterton E18 fault code means: your boiler has too much water inside it, causing the internal pressure to rise to an unsafe level.. It appears on 3 Potterton models in our database.
Technical description: System pressure high (> 2.8 bar)
What causes the Potterton E18 fault?
This fault occurs when the water pressure inside your system exceeds a safe working limit, usually because too much water has been added via the filling loop. It can also happen if the internal parts that manage pressure, such as the expansion vessel, have failed or if a valve is leaking water into the system constantly.
This fault is often seen after homeowners bleed their radiators in autumn or winter and accidentally leave the filling valves open or overfill the system.
DIY fix possible
Check that the silver filling loop valves are tightly closedTurn off the boiler and allow the system to coolBleed a radiator to drain water and reduce system pressure to 1.5 barIf pressure continues to rise after bleeding, call a Gas Safe engineer
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Gas Safe Register →Potterton models that show the E18 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton E18 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