BoilerFaultCodesThe 6 most common faults
Your boiler has switched itself off because it has become too hot internally and needs to cool down for safety.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety switch to prevent damage. It is usually caused by a circulation failure, such as a seized internal pump or a blockage in the system prevents heat from being carried away quickly enough.
Turn the boiler off and allow it to cool for at least 30 minutes.Check that your radiator valves are open and that the system pressure is between 1 and 1.5 bar.Turn the selector switch to the reset position for five seconds and then back to your desired setting.
Your boiler has stopped working because the water pressure in the system has dropped too low and needs topping up.
Why it happens: This fault occurs when the internal water pressure drops below the minimum level required for the boiler to operate safely. The most common reasons are a slow leak from a radiator valve or pipework, or the air being released from the system through recent bleeding of the radiators.
Locate the filling loop (usually a silver flexible hose) underneath the boiler.Slowly open the small valves at either end of the hose until you hear water flowing.Watch the pressure gauge until it reaches between 1 and 1.5 bar, then close both valves tightly.
Your boiler has detected that water is not moving through the system correctly, which could be due to a blockage or a pump failure.
Why it happens: This fault occurs when the boiler detects that water is not moving quickly enough through the internal pipework to carry heat away, causing the system to protect itself from overheating. The most common reason is a failing internal pump that can no longer circulate the water, or a physical blockage caused by a build-up of debris and sludge within the system.
Check that your system pressure is between 1.0 and 1.5 bar on the pressure gaugeEnsure all radiator valves are fully openCheck if any bypass valves are closed
Your boiler has failed to light, which is usually caused by a temporary interruption in the gas supply or a frozen condensate pipe.
Why it happens: This fault occurs when the boiler has tried to ignite several times but failed to detect a flame. The most common reason is a temporary interruption in the gas supply or a blockage in the pipe that carries away waste water. It can also be caused by wear and tear on the internal components that produce the spark or control the gas flow.
Check if other gas appliances in your home, like a hob, are working correctly.If it is freezing outside, check the external plastic condensate pipe for ice and thaw it with warm water.Hold the reset button for five seconds to see if the boiler restarts.
Your boiler has detected an internal electrical error that is preventing it from running safely, and it usually means the main control board is confused or failing.
Why it happens: This fault occurs when the boiler's internal computer becomes confused or fails to monitor its own electronic signals correctly. The most common reason is a failing printed circuit board (PCB) that can no longer communicate with the boiler's components, often triggered by power surges or aging electrical components. In some cases, external electrical interference from a faulty pump or loose wiring can also cause the system to shut down for safety.
Turn the boiler off at the main electrical switchWait 30 seconds before switching it back onPress and hold the 'Reset' button for five seconds
Your boiler is struggling to move water around the system properly, which is causing it to shut down to prevent overheating.
Why it happens: This fault occurs when the water inside the boiler is heating up too quickly because it isn't being pumped away fast enough. The most common reasons are a failed internal pump, a build-up of sludge blocking the pipes, or air trapped within the system that prevents smooth circulation.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barTry bleeding your radiators to remove any trapped air
on the Potterton Promax
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