BoilerFaultCodesThe 6 most common faults
Your boiler has likely overheated, causing a safety switch to trip and shut the system down to protect itself.
Why it happens: This fault occurs when the water temperature inside your boiler gets too high, triggering a safety switch to prevent damage. The most common reason is a lack of water flow, often caused by a failing pump or a blockage within the main heat exchanger. It can also happen if there is trapped air in the system or if the internal safety sensor itself has developed a fault.
Check that your radiator valves are open and not turned to the off position.Ensure there are no blockages in the system such as trapped air by venting (bleeding) your radiators.Wait for the boiler to cool down and press the 'Reset' button.
Your boiler has detected that the water pressure is too low for it to operate safely and has shut down.
Why it happens: This fault occurs when the system water pressure drops below the minimum level required for the boiler to heat up safely. The most common reason is a small leak in the radiator network or pipework, but it can also happen if you have recently bled your radiators without topping the water back up. When the internal sensor detects this lack of pressure, it cuts the power to the burner to prevent the unit from overheating.
Locate the filling loop (a flexible silver hose) underneath or near the boilerSlowly open the one or two taps/levers on the filling loop until you hear water movingWatch the pressure gauge and close the taps when the needle reaches 1.5 bar
Your boiler is struggling to move water through the system, which is causing it to stop running to prevent overheating.
Why it happens: This fault occurs when water is unable to circulate through your boiler's internal pipework fast enough, leading to a rapid rise in temperature. The most common reason is a failing pump that can no longer push the water, though a blockage caused by a build-up of sludge or a stuck internal valve can also restrict the flow. To prevent internal damage from overheating, the boiler safety system shuts the unit down completely.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barTry resetting the boiler to see if the fault clears
Your boiler has failed to light because it isn't receiving enough gas or cannot sense the flame.
Why it happens: This fault occurs when the boiler tries to ignite multiple times but fails to establish or maintain a steady flame. The most common reasons are a temporary interruption in the gas supply, a blocked pipe, or a worn-out internal component that can no longer create a spark or detect the heat.
Check that your gas emergency control valve is open and you have credit on your gas meterCheck if other gas appliances in your home, like a hob, are working correctlyPress and hold the 'Reset' button for five seconds to see if the boiler restartsDuring freezing weather, check if your external condensate pipe is frozen and thaw it with warm water
Your boiler has detected that the water is not moving through the system quickly enough before the burner fires up.
Why it happens: This fault occurs when the boiler's internal sensors detect that water isn't flowing through the heat exchanger as fast as it should. The most common reasons are a failed or sticking pump, air trapped within the system, or a blockage caused by a buildup of sludge and debris.
Check that your boiler pressure is between 1 and 1.5 bar on the gaugeEnsure all radiator valves are fully open to allow water to circulateRestart the boiler using the reset button to see if the error clears
Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
Why it happens: This fault occurs when the internal temperature of the boiler rises above a safe limit, triggering a safety sensor to cut the power. The most common reasons are a failed pump that isn't moving water away from the heat exchanger quickly enough, or a buildup of limescale and sludge that restricts water flow.
Check that your radiator valves are open and not turned to the off position.Ensure your boiler pressure is between 1 and 1.5 bar on the pressure gauge.Press the 'Reset' button (usually a small 'R' or turn the selector knob to 'R' for 5 seconds) to see if the fault clears.
on the Potterton Promax Combi 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