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 sensor to cut the power. The most common reasons are a lack of water flow caused by a failing pump, a blockage in the system, or air trapped within the pipework. Essentially, the heat cannot be moved away from the boiler quickly enough, causing it to overheat.
Check that your boiler pressure is between 1.0 and 1.5 barEnsure all radiator valves and the boiler isolation valves are fully openBleed your radiators to remove trapped air that might be blocking water flow
Your boiler is struggling to move water through the system, which is usually caused by trapped air or a blockage in the pipes.
Why it happens: This fault occurs when water cannot travel through the boiler’s internal heat exchanger quickly enough to carry heat away. The most common reasons are trapped air pockets creating a blockage, a buildup of sludge in the system, or the internal pump failing to spin correctly.
Check that the boiler pressure is between 1 and 1.5 barTurn off the heating and use a radiator key to bleed air from all radiatorsEnsure all radiator valves (TRVs) are fully openReset the boiler using the reset button
Your boiler is struggling to light and stay on, which can sometimes be caused by trapped air in your heating system preventing the water from flowing correctly.
Why it happens: This fault occurs when the boiler tries to light the flame but fails to detect one, causing the system to shut down for safety. The most common reason is that the spark isn't strong enough to ignite the gas, or the sensor that monitors the flame has become dirty or worn out. It can also be triggered if air is trapped in the system, which disturbs the internal pressure and prevents the boiler from operating correctly.
Turn off the boiler and wait for the radiators to cool downUse a radiator key to bleed any air from all radiators in the houseCheck the boiler pressure gauge and top it up to 1.5 bar if it has droppedPress the 'Reset' button on the boiler control panel
Your boiler has lost water pressure or cannot move water around the system, which has caused it to stop working for safety.
Why it happens: This fault occurs when the boiler detects that there is either not enough water in the system or the water is not moving through the pipes as it should. The most common reason is a drop in water pressure due to a minor leak, but it can also happen if the internal pump has seized or becomes blocked with debris.
Check the pressure gauge on the front of the boiler or under the casing.If the needle is below 1 bar, locate the filling loop (braided silver hose) under the boiler.Slowly open the valve(s) until the pressure reaches 1.5 bar, then close them tightly.Restart the boiler to see if the fault clears.
Your boiler has detected a problem with one of its temperature sensors and has stopped working as a safety precaution.
Why it happens: This fault occurs when the boiler's internal computer loses communication with one of the probes that monitors water temperature. The most common reason is that the sensor has physically failed or 'drifted' out of range, meaning it can no longer provide an accurate reading. In some cases, the issue is caused by loose electrical connections or a fault within the main control board itself.
Full guide for E0Your boiler's electronic control centre has developed an internal fault and is unable to communicate with the rest of the system.
Why it happens: This fault occurs when the boiler's internal computer brain suffers a hardware failure or a breakdown in its electronic circuitry. The most common reason is age-related wear to the electrical components on the board, though it can also be triggered by a sudden power surge or moisture getting into the control box.
Full guide for E3on the Baxi Avanta
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