BoilerFaultCodesThe 6 most common faults
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 water inside the boiler reaches an unsafe temperature, triggering a safety switch to kill the power. The most common reasons are a pump failure that prevents water from moving, or a blockage in the system that stops heat from being carried away from the burner.
Allow the boiler to cool down for 30 minutesCheck that your radiator valves are open and not turned to offPress and hold the 'R' or 'Reset' button for five seconds
Your boiler has switched itself off because the water pressure in the system has dropped too low to operate safely.
Why it happens: This fault occurs when the water pressure inside your heating system drops below the minimum level required for the boiler to fire up. The most common reasons are a slow leak from a radiator valve or pipework, or the pressure being manually bled out of the system during radiator venting.
Locate the filling loop (usually a silver flexible hose) underneath your boiler.Slowly open the small tap(s) on the loop until you hear water entering the system.Watch the pressure gauge and close the taps once the needle reaches between 1.0 and 1.5 bar.Check that the error code has cleared; you may need to press 'Reset'.
Your boiler has detected that hot water isn't moving through 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 gets too hot too quickly because it isn't being pumped away effectively. The most common reasons are a seized internal pump, a physical blockage in the pipework, or air trapped within the system preventing proper flow. It can also be triggered if there isn't enough water pressure to allow the circulation to take place.
Check that your system pressure is between 1 and 1.5 bar on the pressure gauge.Ensure all radiator valves and any isolation valves under the boiler are fully open.Listen for air trapped in the system and bleed your radiators if necessary.
Your boiler is failing to light the gas flame, which means you currently have no heating or hot water.
Why it happens: This fault occurs when the boiler is unable to establishes a flame after several attempts, typically because the fuel isn't reaching the burner or the spark isn't igniting it. The most common reasons include a lack of gas supply, a blocked condensate pipe, or worn-out internal components like the ignition electrodes.
Check if your gas meter has credit (if prepay) or if other gas appliances like your hob are working.Press and hold the 'Reset' button for five seconds to see if the boiler restarts.If it is freezing outside, check if the white plastic condensate pipe leading outdoors is frozen and thaw it with warm water.
Your boiler's internal computer has encountered a memory or electrical glitch and has temporarily locked itself down to prevent safety issues.
Why it happens: This fault occurs when the boiler's control board experiences a communication failure or an internal memory error, often caused by unstable electrical supply or aging components. It essentially means the boiler is 'confused' by inconsistent data and has shut down as a safety precaution to avoid operating unpredictably.
Locate the selector switch on the front of the boilerTurn the switch to the 'R' (Reset) position and hold for 5 secondsRelease the switch and wait for the boiler to attempt a restart
Your boiler has detected that water is not moving through the system correctly, which causes it to shut down to prevent overheating.
Why it happens: This fault occurs when the boiler's internal sensors detect that water is heating up too quickly because it isn't being moved away from the burner fast enough. The most common reason is a seized or failing pump, though it can also be caused by a build-up of air or debris physically blocking the water's path through the heat exchanger.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barBleed all radiators to remove trapped air from the system
on the Baxi Duo-tec/Megaflo
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 Baxi 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