BoilerFaultCodesMain E125 Fault Code
The Main E125 fault code means: your boiler is struggling to move hot water around the system, which is usually caused by a blockage or a pump issue that is preventing the unit from cooling itself down.. It appears on 5 Main models in our database.
Technical description: Circulation error
What causes the Main E125 fault?
This fault occurs when the boiler detects that water is not moving through the system quickly enough to carry heat away from the burner. The most common reasons are a failed internal pump that can no longer push the water, or a build-up of debris and sludge that has physically blocked the pipes or heat exchanger. Effectively, the boiler shuts down because it is getting too hot too quickly and needs to prevent internal damage.
This fault is more common in autumn and winter when the heating is first switched back on, as debris often settles and solidifies during the summer months when the pump is inactive.
DIY fix possible
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 bar on the gaugeGently bleed air from your radiators using a radiator key
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Gas Safe Register →Main models that show the E125 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main E125 fault code information on this page is sourced and cross-checked against the official Main service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026