BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the internal fan, which safely exhausts gases, is unable to start or spin at the correct speed.
Why it happens: This fault occurs when the boiler's control board cannot detect the fan spinning at the speed required to safely clear waste gases from the system. The most common physical causes are a buildup of dirt or debris in the fan blades, a complete motor failure, or a loose electrical connection between the fan and the main circuit board.
Full guide for FAN LOCKOUTYour boiler has detected a faulty temperature sensor which means it can no longer accurately monitor how hot the water is getting.
Why it happens: This fault occurs when the internal temperature sensor fails to send a reliable signal to the main control board, often due to internal corrosion or electrical fatigue. Because the boiler can no longer track how hot the water is, it shuts down as a safety precaution to prevent the system from overheating. In some cases, the problem can also be caused by loose or damaged wiring that has broken the connection between the sensor and the brain of the boiler.
Full guide for THERMISTORYour boiler has detected that it is running without enough water inside, which means it cannot safely heat your home and has shut itself down to prevent damage.
Check your boiler pressure gauge; if it is below 1 bar, you need to repressurise the system.Locate the filling loop (usually a silver braided hose with one or two valves) connected to the boiler pipes.Slowly open the valve(s) to allow water to enter until the gauge needle reaches between 1 and 1.5 bar, then turn the valve(s) firmly off.
Your boiler has stopped working because a sensor that measures water temperature is providing incorrect information or has failed.
Full guide for On Flash OnYour boiler is failing to run because it isn't receiving enough electricity from your home's power supply.
Full guide for Flash Off FlashYour boiler has lost its internal connection to the control panel, causing it to stop operating completely.
Full guide for On On Onon the Potterton Promax 15/2 HE Plus
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Potterton shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue