BoilerFaultCodesThe 6 most common faults
Your boiler has detected a problem with how it disposes of waste gases or a blockage in its drainage system, causing it to shut down for safety.
Check the external condensate pipe for signs of freezing if the weather is very coldThaw any frozen external pipes using warm (not boiling) waterCheck the flue terminal on the outside of your house for any obvious obstructions like debris or bird nestsPress the Reset button for five seconds
Your boiler has likely overheated, causing a safety sensor to automatically shut the system down to prevent damage.
Check that your radiator valves are open and not turned off.Ensure your system pressure is topped up to between 1 and 1.5 bar.Allow the boiler to cool down for 30 minutes and then press the 'Reset' button.
Your boiler has stopped working because the water pressure is too low for it to operate safely.
Locate the filling loop (usually blue levers or a braided hose under the boiler)Slowly open the valves until you hear water flowing and the gauge reaches between 1 and 1.5 barClose both valves fully and press the 'R' or 'Reset' button on the boiler
Your boiler has detected that water is not circulating correctly around the system, which is usually caused by an air lock or a pump failure.
Ensure all radiator valves are fully openBleed all radiators to remove trapped airCheck that the boiler pressure is between 1 and 1.5 bar on the gaugeTry resetting the boiler using the reset button
Your boiler has failed to light because it either isn't receiving gas or the system cannot detect a flame.
Check that your gas emergency control valve is open and any prepay meter has creditPress and hold the 'R' or Reset button for 5 secondsIn freezing temperatures, check if the white plastic condensate pipe outside is frozen and thaw with warm water
Your boiler has detected that water is not circulating correctly through the system before the burner ignites, often caused by trapped air or a blockage.
Check that all radiator valves and boiler isolation valves are fully openBleed all radiators to remove any trapped air pocketsEnsure the system pressure is between 1.0 and 1.5 bar on the gauge
on the Baxi 800
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