BoilerFaultCodesThe 6 most common faults
Your boiler has detected that there is not enough water in the central heating system to operate safely.
Locate the filling loop (the silver braided hose) underneath the boiler.Slowly open the blue or black taps on the filling loop until you hear water flowing.Monitor the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps fully.
Your boiler has detected that water is not moving through the system properly, often because the water pressure is too low.
Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.Locate the filling loop (the silver braided hose) underneath the boiler.Open the valves slowly to top up the water pressure until the gauge reaches 1.2 bar, then close them tightly.Restart the boiler to clear the fault.
Your boiler has temporarily stopped working because the water pressure inside the heating system has dropped too low.
Locate the filling loop or key underneath your boiler or near the pipework.Open the valves slowly to let water into the system until the pressure gauge on the front reaches between 1 and 1.5 bar.Close the valves tightly and press the reset button on your boiler if it does not restart automatically.
Your boiler has stopped running because it has lost the signal from your external heating controls, such as your room thermostat or programmer.
Check if your room thermostat or programmer has power or needs new batteries.Ensure your smart home hub or Wi-Fi router is switched on and connected.Verify that the heating is actually turned 'on' at your wall controls.
Your boiler is not receiving enough electrical power from your home's mains supply to operate safely.
Check if there is a partial power cut or 'brownout' in your local areaEnsure the boiler's fused spur switch is fully engaged and not damagedSwitch the boiler off at the main spur, wait 30 seconds, and switch it back on to reset the electronics
Your boiler has sensed an unusual temperature gap between the water leaving and returning to the unit, suggesting the water isn't flowing through your heating system correctly.
Ensure all radiator valves (TRVs) are fully openCheck that the boiler pressure is between 1.0 and 1.5 bar on the gaugeGently bleed your radiators to remove trapped air
on the Baxi 800 System 2
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
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
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