BoilerFaultCodesPotterton E12 Fault Code
The Potterton E12 fault code means: your boiler is struggling to pump water around the system, often because the water pressure is too low or there is a blockage or air bubble preventing flow.. It appears on 3 Potterton models in our database.
Technical description: Differential water flow switch is still open
What causes the Potterton E12 fault?
This fault occurs when the boiler's internal sensors detect that water isn't moving through the unit quickly enough to safely carry heat away. The most common reason is that the system pressure has dropped too low, but it can also be caused by a build-up of sludge or a large air bubble trapped inside the pump. In these cases, the boiler shuts down as a safety precaution to prevent the heat exchanger from overheating.
This fault is frequently seen in autumn when heating systems are turned back on after a long summer break, as pumps can seize or air pockets can settle during periods of inactivity.
DIY fix possible
Check the pressure gauge on the front of the boiler and top it up to 1.5 bar if it is low.Ensure all radiator valves are fully open.Try bleeding your radiators to remove any trapped air.Reset the boiler to see if the fault clears.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Potterton models that show the E12 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton E12 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