BoilerFaultCodesThe 6 most common faults
Your boiler is struggling to breathe because something is blocking the passage of air or exhaust gases through the flue pipe.
Why it happens: This fault occurs when the boiler detects that air isn't moving through the system correctly, usually because something is physically blocking the flue pipe or the internal air pathways. It is often caused by debris like leaves or a bird's nest in the external pipe, or a failing internal fan that can no longer push the exhaust gases out of your home safely.
Check the external flue pipe terminal outside your home for obvious obstructions like bird nests, leaves, or debris.During winter, check if the flue outlet is blocked by heavy snow or icicles.Reset the boiler by turning the selector switch to 'R' for five seconds after removing any external blockage.
Your boiler is struggling to move water around the system properly, which is causing it to overheat and shut down for safety.
Why it happens: This fault happens because the water inside your boiler is heating up too fast and cannot flow away into your radiators quickly enough. The most common reasons are a pump that has failed or become jammed, or a blockage within the pipework caused by a buildup of sludge and debris.
Check that your boiler pressure gauge is between 1 and 1.5 barEnsure all radiator valves and the external isolation valves under the boiler are fully openGently bleed your radiators to remove any trapped air pockets
Your boiler has become too hot and has shut itself down for safety, likely because the water isn't moving through the system correctly.
Why it happens: This fault occurs when the water inside the boiler exceeds a safe temperature limit, triggering a safety sensor to cut the power. The most common reason is that the internal pump has failed or seized, meaning the heat generated by the burner cannot be carried away to your radiators. It can also be caused by a blockage in the pipework or a build-up of air preventing the water from circulating properly.
Check that your radiator valves are open to allow water to flow.Check the boiler pressure gauge and top up to 1.5 bar if it is too low.Press the Reset button once to see if the system restarts.
Your boiler has shut down because there is too much water pressure in the system, which could lead to leaks if not addressed.
Why it happens: This fault occurs when the water pressure inside your heating system rises above a safe operating level, triggering a safety shutdown. The most common reasons are that the filling loop was left slightly open after topping up the system, or an internal component like the expansion vessel has failed and can no longer manage the pressure changes as the water heats up.
Check that the filling loop valves are tightly closedTurn off the boiler and allow the system to coolBleed water from a radiator using a bleed key to reduce pressureMonitor the pressure gauge until it returns to between 1.0 and 1.5 bar
Your boiler has stopped working because the water pressure in the central heating system has dropped too low.
Why it happens: This fault occurs when the water pressure inside your heating system drops below the minimum level required for the boiler to operate safely. The most common reason is a slow leak from a radiator valve or joint, though pressure can also drop if you have recently bled your radiators and haven't topped the water back up.
Locate the filling loop (the silver flexible hose usually found under the boiler).Open the small black valves slowly until you hear water flowing.Watch the pressure gauge and close the valves once it reaches between 1.0 and 1.5 bar.
Your boiler has detected that hot water is not moving around the system properly, causing it to shut down to prevent overheating.
Why it happens: This fault occurs when water is unable to flow through the boiler quickly enough, leading to a sudden rise in temperature. The most common reason is a failed internal pump or a blockage in the system caused by a buildup of sludge and debris. It can also happen if there is an air lock or if the radiator valves are all turned off, preventing the heat from escaping.
Check that the boiler pressure is between 1.0 and 1.5 bar on the pressure gaugeEnsure all radiator valves are fully openCheck if any air is trapped in your radiators and bleed them if necessaryRestart the boiler by turning the selector switch to the 'R' position for five seconds
on the Potterton Promax 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