BoilerFaultCodesThe 6 most common faults
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 tried and failed to light its burner four times, meaning it cannot provide heating or hot water until the issue is resolved.
Check if your gas supply is active by testing another gas appliance like a hobEnsure your gas meter has credit and the handle is in the 'on' positionPress the 'Reset' button on the boiler control panel for five seconds
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 shut down because it thinks the water inside is getting too hot or a temperature sensor has malfunctioned.
Turn the boiler power off and then back on to reset the electronicsCheck that all radiator valves are fully open to allow water to circulateEnsure the central heating system pressure is between 1 and 1.5 bar on the gauge
Your boiler has stopped working because the water pressure inside your heating system has dropped too low to function safely.
Locate the filling loop (a silver braided hose) underneath the boiler.Open the valves on both ends of the loop to allow water into the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (usually 1.0 to 1.5 bar).Close both valves tightly and ensure the pressure remains stable.
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
on the Baxi 436 COMBI 2.1
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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