BoilerFaultCodesThe 6 most common faults
Your boiler has overheated, prompting a safety switch to shut the system down to prevent damage.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety sensor to cut the power. The most common reasons are a failed pump stopping water from moving or a blockage in the heat exchanger caused by a buildup of sludge and debris.
Check that all radiator valves are fully openEnsure the system pressure is between 1.0 and 1.5 barAllow the boiler to cool down and then press the 'Reset' button
Your boiler has detected that the water pressure in the system is too low to run safely.
Why it happens: This fault occurs when the internal sensor detects that the water pressure has dropped below the minimum level required for the boiler to operate. The most common reason is a small leak somewhere in your radiator system or air being released through a valve, which reduces the overall volume of water. Without enough water pressure, the boiler shuts down to prevent the heat exchanger from overheating or becoming damaged.
Locate the external or internal filling loop (usually silver flexible hoses with blue or black handles).Slowly open the valves until you hear water flowing into the boiler.Monitor the pressure gauge on the front of the boiler until it reaches between 1.0 and 1.5 bar, then close the valves tightly.The boiler should reset automatically, but you may need to press the 'R' or reset button if the code persists.
Your boiler has shut down because it is getting too hot inside, usually because the water isn't moving around the system properly.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature because it isn't being moved away into your radiators or hot water tap quickly enough. The most common reason is that the internal pump has failed or is stuck, but it can also be caused by a large air bubble trapped in the pipework blocking the flow.
Check that all radiator valves are open and not turned off.Ensure there is enough water pressure in the system (typically 1.0 to 1.5 bar).Gently bleed your radiators to remove any trapped air that might be blocking water flow.
Your boiler has tried to light several times but cannot establish a steady flame, likely because gas isn't reaching it or the spark is failing.
Why it happens: This fault occurs when the boiler has tried to ignite five times but failed to detect a flame, causing the system to shut down for safety. It is most commonly caused by an interruption in the gas supply, a blocked burner, or a worn-out spark electrode that can no longer create a strong enough light. In some cases, a faulty internal sensor may simply fail to 'see' the flame even if the boiler has actually lit.
Check that your gas meter has credit and the emergency control valve is open.Verify if other gas appliances, like a hob, are working to confirm gas supply.Check if the condensate pipe (outside white plastic pipe) is frozen or blocked.Press and hold the reset button for five seconds.
Your boiler has stopped working because a sensor that monitors the temperature of the water returning to the unit has developed a fault.
Why it happens: This fault occurs when the boiler's control board loses communication with the sensor that monitors water temperature coming back from your radiators. The most common reason is that the internal components of the sensor have failed due to age or wear, but it can also be caused by loose or damaged electrical wiring. Since the boiler cannot safely monitor how hot the water is, it shuts down as a safety precaution.
Full guide for E20Your boiler's computer brain is not correctly configured or matches the wrong model, meaning the system cannot operate safely or reliably.
Why it happens: This fault occurs when the internal safety sensor detects that the exhaust gases are either too hot or the sensor itself has developed an electrical failure. The most common reason is a build-up of debris or heat damage within the sensor, preventing it from sending a reliable signal to the main control board.
Full guide for E28on the Potterton Gold Combi HE
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