BoilerFaultCodes
The most common Worcester Bosch faults
Your boiler has detected that there is not enough water circulating through the system to operate safely.
Why it happens: This fault occurs when the boiler's internal sensors detect air pockets or a significant drop in water pressure, preventing the pump from moving water around. The most common cause is a leak in the system or radiators that have recently been bled, leaving the boiler with insufficient water to operate safely. Without enough water to act as a lubricant and coolant, the pump 'runs dry' and the system shuts down to prevent heat damage.
Check your boiler's pressure gauge to see if it is below 1 barLocate the filling loop (usually silver braided hoses under the boiler)Slowly open the valves until the pressure reaches 1.5 bar, then close them tightly
Your boiler has lost its connection with the thermostat, meaning they are no longer speaking to each other to control your heating.
Why it happens: This fault occurs when the wireless link between your boiler and your wall thermostat is broken, preventing the boiler from receiving instructions to turn on. The most common reasons are dead batteries in the thermostat unit or an obstruction like a new piece of metal furniture blocking the radio signal between the devices.
Check if your thermostat batteries need replacingEnsure the thermostat is within range and has no obstructionsTurn the power to the boiler off and back on to restart the connection
Your boiler has stopped working because the fan cannot properly push exhaust fumes out or pull fresh air in through the flue pipe.
Why it happens: This fault occurs when the boiler's internal safety sensors detect that the fan is not moving air through the system at the required speed. The most common reasons are a physical blockage in the flue pipe outside, a build-up of debris within the fan itself, or a failure in the electronic sensor that monitors air pressure.
Check the external flue pipe for obvious visual obstructions like bird nests, leaves, or debrisEnsure the external flue terminal is not covered by garden furniture or building materialsGently clear any visible snow or ice buildup from the flue outlet
Your boiler has sensed that it is getting too hot and has automatically shut down for safety.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety switch to kill the power. The most common reasons are a pump failure that stops water from moving around the system or a build-up of debris causing a blockage in the heat exchanger.
Check that your system pressure is between 1 and 1.5 bar on the front gaugeTop up the water pressure using the white internal or external filling loop if it is too lowEnsure all radiator valves are fully open and there are no blockagesPress the 'reset' button on the boiler control panel once pressure is corrected
Your boiler has stopped working because it cannot light a flame, most likely due to an interruption in the gas supply or a part that has worn out.
Why it happens: This fault occurs when the boiler tries to start up but fails to detect a steady flame after several attempts. The most common reasons are a temporary interruption in your gas supply, a build-up of carbon on the internal sensors, or a component failure like a worn-out ignition lead.
Check if other gas appliances, like a hob, are working to confirm your gas supply is onIf you have a prepaid meter, ensure you have sufficient creditPress and hold the 'Reset' button for five seconds to see if the boiler restartsIn freezing weather, check if your white plastic condensate pipe outside has frozen and gently thaw it with warm water
Your boiler's internal computer has encountered a glitch or a hardware failure, preventing it from running properly.
Why it happens: This fault occurs when the boiler's main control board loses its ability to process data correctly or experiences a communication breakdown between internal components. It is often caused by a sudden electrical surge, moisture entering the control box, or simply the natural degradation of the solder points and microprocessors over time.
Switch the boiler off at the fused spur or power switchWait 30 seconds and switch the power back onPress and hold the Reset button for 5 secondsIf the code persists, contact a Gas Safe engineer to inspect the internal electronics
Your boiler has entered a temporary lock-out mode because a service engineer's diagnostic tool was recently plugged in and has not been properly disconnected or reset.
Why it happens: This fault occurs when the boiler's internal computer remains in 'diagnostic mode' after being connected to a technician's service tool. It signifies that the communication between the boiler and the external hardware was interrupted or not closed down correctly, causing the system to stay frozen for safety. In most cases, it is simply a digital hang-up rather than a component failure.
Locate the reset button on the boiler control panel.Press and hold the reset button for 5 seconds.Wait for the boiler to complete its startup sequence; if the code persists, a technician may need to re-insert and properly exit their diagnostic software.
Your boiler has lost power or experienced an electrical error while it was already trying to show a different fault code.
Why it happens: This fault occurs when the boiler loses electrical power at the exact moment it was trying to record or display a different technical error. It is usually caused by a loose connection in the internal wiring or a failing main circuit board that can no longer process electrical signals correctly. Essentially, the boiler's internal computer has crashed while trying to report a problem, leaving it in a confused state.
Locate the reset button on the front control panelPress and hold the reset button for five secondsWait for the boiler to restart and see if a different fault code appears