BoilerFaultCodesThe 6 most common faults
Your boiler is experiencing a communication error or internal electronic fault that is preventing it from running properly.
Why it happens: This fault occurs when the boiler's internal computer, the Printed Circuit Board, loses the ability to send or receive messages from other components. It is often caused by a loose connection in the wiring or a hardware failure within the control board itself. Think of it like a computer crash where the system can no longer tell the boiler how to operate safely.
Locate the selector switch on the front of the boiler.Turn the switch to the 'Reset' position and hold it for five seconds.Turn the switch back to the 'On' position and wait for the boiler to restart.
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 heat exchanger reaches an unsafe temperature, triggering a safety sensor to cut the power. The most common reasons are a pump failure preventing water from moving through the system or a blockage such as lime scale or sludge restricting the flow. Sometimes, the overheat thermostat itself has simply become faulty and is sending a false signal to the control board.
Check that your radiator valves are open and not turned to off or zeroEnsure your system water pressure is between 1 and 1.5 bar on the pressure gaugeTurn the selector switch to the reset position for five seconds and then back to your desired setting
Your boiler has tried to light itself several times but cannot create a flame, meaning you will not have any heating or hot water until it is reset or repaired.
Why it happens: This fault occurs when the boiler is unable to detect a steady flame after several attempts to ignite the gas. The most common reasons are a lack of gas supply reaching the unit, worn-out ignition components that can't create a spark, or a dirty internal sensor that cannot tell the boiler the flame is lit.
Check that your gas emergency control valve is open and you have credit on your gas meterTurn the selector switch to the 'R' (Reset) position for at least five secondsRelease the switch and see if the boiler initiates a successful ignition sequence
Your boiler has detected a general internal error, often linked to a small electronic glitch or a sensor that is failing to communicate correctly with the main controls.
Why it happens: This fault occurs when the boiler's internal computer receives conflicting information or loses contact with the main components that manage the heating process. It is typically caused by a communication breakdown between the electronic control board and the sensors, or small electrical fluctuations that disrupt the system's logic. In many cases, it indicates that the 'brain' of the boiler is no longer able to safely coordinate the startup sequence.
Locate the reset knob on the front control panelTurn the knob to the 'R' (Reset) position and hold for 5 secondsRelease the knob and wait to see if the error light clears and the boiler restarts
Your boiler has detected an issue with the ventilation fan, which means it cannot safely clear exhaust fumes and will not ignite.
Why it happens: This fault occurs when the boiler's control system senses that the fan is not spinning at the correct speed to safely expel waste gases. The most common reasons are a mechanical failure of the fan motor itself, a loose connection in the wiring, or a fault on the main circuit board that prevents power from reaching the fan.
Full guide for 4 Red FlashesYour boiler's internal memory chip has developed a software or connection error, meaning it can no longer remember its correct settings to operate.
Why it happens: This fault occurs when the boiler's internal memory chip fails to communicate with the main control board, similar to a corrupted file on a computer. It is usually caused by a hardware failure within the chip itself or a loose physical connection on the circuit board that prevents the boiler from reading its essential operating instructions. Because the boiler no longer knows its own safety limits or settings, it shuts down immediately as a precaution.
Full guide for 5 Red Flasheson the Baxi MainEco
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