BoilerFaultCodesThe 6 most common faults
Your boiler is struggling to pump water around the system, often because the water pressure is too low or there is a blockage or air bubble preventing flow.
Why it happens: This fault occurs when the boiler's internal sensors detect that water isn't moving through the unit quickly enough to safely carry heat away. The most common reason is that the system pressure has dropped too low, but it can also be caused by a build-up of sludge or a large air bubble trapped inside the pump. In these cases, the boiler shuts down as a safety precaution to prevent the heat exchanger from overheating.
Check the pressure gauge on the front of the boiler and top it up to 1.5 bar if it is low.Ensure all radiator valves are fully open.Try bleeding your radiators to remove any trapped air.Reset the boiler to see if the fault clears.
Your boiler has detected that water is not circulating correctly before the burner lights, which usually means there is a blockage or a pump issue.
Why it happens: This fault occurs when the boiler's internal sensors detect that water isn't moving through the unit quickly enough before the flames ignite. The most common reasons are a seized central heating pump that can't push the water around, or a build-up of sludge and debris creating a physical blockage in the heat exchanger.
Ensure your radiator valves are open to allow water flowCheck that the boiler pressure is between 1 and 1.5 bar on the gaugeRestart the boiler by pressing the reset button for five seconds
Your boiler has shut down because it grew too hot too quickly, usually because the water inside isn't circulating properly.
Why it happens: This fault happens when the water inside the boiler gets too hot too quickly, triggering a safety shut-off to prevent damage. It is usually caused by a blockage or a pump failure that stops the water from moving through the system and carrying the heat away. Common culprits include a seized pump, a buildup of air in the pipes, or a physical blockage like limescale or sludge.
Wait for the boiler to cool down completelyCheck that all radiator valves and the boiler isolation valves are fully openPress the Reset button for five secondsGently bleed your radiators to remove any trapped air pockets
Your boiler has detected that there is not enough water pressure in the system to operate safely, causing it to shut down.
Why it happens: This fault occurs when the water level inside your heating system drops below the minimum required amount, making it unsafe for the boiler to fire up. The most common reasons for this drop are a small leak in the pipework or radiators, or the need to bleed air from the system after a period of inactivity. If the pressure continues to drop after you refill it, a component inside the boiler like the expansion vessel may be failing.
Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.Slowly open the one or two taps on the filling loop until you hear water flowing.Monitor the pressure gauge and close the taps when the needle reaches between 1 and 1.5 bar.
Your boiler is struggling to move heated water through the system effectively, which is causing it to stop for protection.
Why it happens: This fault occurs when the boiler detects that water is not moving through the internal pipework fast enough to carry heat away from the burner. The most common reasons are a failed internal pump that can no longer push the water, or a blockage caused by a build-up of debris and sludge within the system. Because the water stays still and overheats rapidly, the boiler shuts down to prevent damage to the heat exchanger.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1 and 1.5 bar on the gaugeBleed your radiators to remove any trapped air pockets
Your boiler has failed to light a flame, which is usually caused by a temporary interruption in the gas supply or a frozen condensation 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 cause is a blockage in the condensation pipe or a temporary interruption in your gas supply, though it can also be caused by worn internal components like the ignition electrodes.
Check that your gas meter has credit and the isolation valve is openIf it is freezing outside, check if the plastic condensation pipe leading outdoors is frozen and thaw it with warm waterPress and hold the 'Reset' button for five seconds to restart the ignition sequence
on the Potterton Assure Combi / System
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