BoilerFaultCodesPotterton 125 Fault Code
The Potterton 125 fault code means: your boiler is struggling to move water around the system correctly, which is causing it to shut down to prevent overheating.. It appears on 1 Potterton model in our database.
Technical description: Primary circulation fault or pump failure
What causes the Potterton 125 fault?
This fault occurs when the water inside the boiler gets too hot too quickly because it isn't being pushed away into your radiators or hot water tank. The most common reason is that the internal pump has failed or is physically jammed, but it can also be caused by a build-up of sludge blocking the pipework or an airlock trapped in the system.
This issue is frequently seen in autumn when heating systems are switched back on after being idle all summer, which can cause the pump to seize.
DIY fix possible
Check that your radiator valves are openEnsure your boiler pressure is between 1.0 and 1.5 bar on the pressure gaugeGently bleed your radiators to remove trapped air
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Potterton models that show the 125 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton 125 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