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 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 communication error or software glitch that is preventing it from running safely.
Why it happens: This fault occurs when the boiler's main control centre suffers a sudden communication breakdown between its internal electronic components. It is typically caused by a component failure on the circuit board or a loose connection in the wiring harness that prevents the computer from verifying its own safety checks. Because the 'brain' of the boiler can no longer guarantee safe operation, it shuts the system down immediately.
Press and hold the reset button for five secondsWait for the boiler to complete its restart sequenceIf the code persists, turn the main power switch to the boiler off and back on again
Your boiler has encountered an internal electronic communication error that is preventing it from running safely.
Why it happens: This fault occurs when the boiler's internal computer brain fails to communicate properly with the other sensors and components inside the unit. It is usually caused by a physical failure of the main circuit board or a loose connection in the internal wiring harness that prevents data from traveling through the system. Because the boiler cannot verify that it is operating safely, it stops running as a protective measure.
Press the 'Reset' button on the control panel once.Wait up to 15 minutes for the boiler to restart.If the code persists, do not attempt further repairs and contact a Gas Safe engineer.
Your boiler appears to have no power and the display is completely dead, meaning it cannot provide any heating or hot water.
Why it happens: This fault occurs when the electrical circuit inside the boiler is interrupted, preventing power from reaching the internal components. The most common reason is a blown internal fuse or a failure within the transformer, which acts as the heart of the boiler's electrical system. In some cases, a power surge or a short circuit on the main control board can cause the unit to shut down completely to prevent further damage.
Check if the main electricity switch for the boiler is turned onCheck your home's consumer unit (fuse box) to see if a circuit breaker has trippedReplace the fuse in the external boiler spur switch with a new 3-amp fuse
Your boiler appears to have lost all electrical power, meaning it cannot start up or provide any heating or hot water.
Why it happens: This fault occurs when the boiler's control system is no longer receiving the electrical current it needs to operate. The most common reason is a blown internal glass fuse or a failure within the main circuit board, often triggered by a sudden power surge or water leaking onto electrical components. Effectively, the boiler has lost its 'brain' and cannot communicate with any other parts of the system.
Check if other appliances in your home have powerEnsure the boiler's electrical isolation switch is turned onCheck your home's main fuse box (consumer unit) for any tripped circuit breakers
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