BoilerFaultCodesThe 6 most common faults
Your boiler has shut down because water intended for your drain is backing up and has triggered a safety sensor.
Why it happens: This fault occurs when the internal tank that collects waste water becomes full and cannot empty itself properly. The most common reasons are a mechanical failure of the condensate pump or a blockage in the thin plastic discharge pipe leading away from the boiler. To prevent an internal flood, a safety sensor triggers and shuts the system down until the water level drops.
Check if the condensate pump is plugged in and turned on at the wall.Inspect the thin plastic pipe leading from the pump for any kinks or blockages.If the weather is freezing, check if the external waste pipe is frozen and thaw it with warm (not boiling) water.
Your boiler's fan, which safely clears exhaust gases from the unit, has stopped spinning correctly and prevented the system from firing up.
Why it happens: This fault occurs when the boiler's control board tries to start the fan but doesn't receive the correct signal that it is spinning at the right speed. The most common reasons are a build-up of debris causing the fan to seize or an electrical failure within the fan's motor or the main circuit board. Without the fan running correctly, the boiler cannot safely remove exhaust gases, so it shut downs for safety.
Full guide for FAN LOCKOUTYour boiler's internal temperature sensor has stopped sending a reliable signal, which means the system cannot safely monitor how hot the water is getting.
Why it happens: This fault occurs when the boiler's internal thermometer, called a thermistor, fails to measure the water temperature correctly. The most common reason is that the sensor has physically degraded over time or developed an electrical short, though it can also be caused by loose or corroded wiring to the main control board.
Full guide for THERMISTORYour boiler has stopped working because the pipe that drains away waste water is blocked, causing the system to temporarily shut down to prevent internal damage.
Locate the plastic condensate pipe exiting your boiler or property near the exterior wall.Check the end of the pipe outside for blockages like ice, leaves, or debris.If the pipe is frozen, pour warm (not boiling) water over the frozen section to thaw it out.Reset your boiler using the reset button on the control panel.
Your boiler has failed to start after several attempts because it cannot safely light its internal flame.
Full guide for Ignition LockoutYour boiler has detected that it is getting too hot and has automatically shut itself down to prevent damage to its internal components.
Full guide for OVERHEAT LOCKOUTon the Potterton Promax FSB 30HE
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