BoilerFaultCodesPotterton E118 Fault Code
The Potterton E118 fault code means: your boiler has detected that there is not enough water pressure in the system to operate safely, causing it to shut down.. It appears on 2 Potterton models in our database.
Technical description: Primary system water pressure too low
What causes the Potterton E118 fault?
This fault occurs when the water level inside your heating system drops below the minimum required amount, making it unsafe for the boiler to fire up. The most common reasons for this drop are a small leak in the pipework or radiators, or the need to bleed air from the system after a period of inactivity. If the pressure continues to drop after you refill it, a component inside the boiler like the expansion vessel may be failing.
This code is frequently seen in autumn when homeowners turn their heating back on for the first time, as small leaks or trapped air can cause the pressure to dip during the summer months.
DIY fix possible
Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.Slowly open the one or two taps on the filling loop until you hear water flowing.Monitor the pressure gauge and close the taps when the needle reaches between 1 and 1.5 bar.
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Gas Safe Register →Potterton models that show the E118 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton E118 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