151 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: 35 CDI
This boiler uses LED flash patterns
Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →
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Your boiler has detected a communication error with its internal computer chip or a problem with the fan system, causing it to shut down for safety.
Your boiler is currently stuck in a testing mode used by engineers and needs to be switched back to its normal operating setting.
Your boiler is accidentally stuck in a technician's test mode, meaning it is set to run at its highest power rather than responding to your thermostat.
Your boiler's internal computer parts do not recognise each other and are unable to communicate, preventing the system from starting up.
Your boiler’s internal computer chip does not match the main control board, preventing the system from operating for safety reasons.
Your boiler's internal computer memory chip has developed a fault or is not communicating correctly, causing the system to shut down for safety.
Your boiler is not suffering from a fault; it is simply indicating that it is currently operating to provide central heating for your home.
Your boiler is currently working correctly and is simply notifying you that it is running in central heating mode.
Your boiler is simply indicating that it is currently busy heating your hot water.
Your boiler is simply notifying you that it is currently busy heating up your tap water.
Your boiler is currently on standby because it has received a signal from your thermostat to start heating and is preparing to fire up.
Your boiler has temporarily paused its burner to prevent it from switching on and off too frequently, which helps protect the internal components from wear and tear.
Your boiler is basically having a short rest because it has reached the required temperature or there is currently no demand for heating or hot water.
Your boiler is working fine but is currently sitting idle because your thermostat or hot water tap hasn't asked it to turn on.
Your boiler is temporarily pausing because the water inside is currently hotter than the temperature you have requested.
Your boiler has paused because the water inside has become hotter than the temperature you have requested on the dial.
Your boiler is currently running at its maximum power setting used by engineers for testing, so it won't respond to your normal thermostat controls.
Your boiler is currently set to a manual testing mode used by engineers to check emissions and is not experiencing an actual fault.
Your boiler is heating up much faster than it should, causing it to shut down to prevent overheating.
Your boiler has shut down because it has detected it is getting too hot, usually caused by the water pressure being too low.
Your boiler is displaying a status message indicating that a professional diagnostic tool was recently plugged into the system's internal memory menu.
Your boiler is failing to light the gas even though it is trying to, which means it cannot provide any heating or hot water until it is fixed.
Your boiler thinks it sees a flame even though it hasn't ignited yet, which prevents it from starting up safely.
Your boiler's computer brains are not speaking the same language and need a software update or a component reset to work together correctly.
Your boiler has shut down because it cannot detect heat moving from the burner into your heating system, usually because water is not circulating properly.
Your boiler is temporarily running at a lower power setting because it has already reached its target temperature and is waiting for the system to cool down slightly before firing up again.
Your boiler is currently running a self-diagnostic check, which is usually a temporary sequence that occurs during startup or after a reset.
Your boiler is currently increasing its power to meet your heating or hot water needs, which is a normal part of its operation.
Your boiler is currently going through its normal startup sequence and is getting ready to light the burner.
Your boiler has detected an internal electrical issue or a wiring fault that is preventing it from safely managing the gas flow.
Your boiler is temporarily finishing a hot water task before it switches back to heating mode.
Your boiler is temporarily pausing the hot water production to prevent itself from overheating or cycling too frequently.
Your boiler is still detecting a flame even though the gas supply should be shut off, which is a safety fault that requires a professional inspection.
Your boiler has detected an issue with the electricity supply entering the unit, which is preventing it from running safely.
Your boiler is not receiving enough stable electricity from the mains supply to operate safely.
Your boiler's internal computer chips are not communicating correctly or do not match, preventing the system from starting up.
Your boiler’s internal computer chip is not communicating correctly with the main control board, meaning the system doesn't recognise its own settings.
Your boiler's internal temperature sensors are giving conflicting readings, likely because a sensor has failed or become dislodged.
Your boiler has lost its internal connection to the smart controls or sensors, meaning the main components are no longer talking to each other correctly.
Your boiler has detected that the water pressure is too low for it to operate safely, which usually means it needs more water added to the system.
Your boiler's hot water sensor is not working correctly or has become unplugged, meaning the system cannot safely monitor the temperature of your tap water.
Your boiler is having trouble measuring the temperature of its stored hot water, which may prevent it from heating your water correctly.
Your boiler has lost contact with the outdoor thermometer that helps it adjust to the weather, which may make your heating less efficient.
Your boiler's internal pressure monitor is either disconnected or broken, meaning the system has shut down because it cannot confirm it is safe to run.
Your boiler has lost connection to the sensor that measures the temperature outside, meaning it may not heat your home as efficiently as usual.
Your boiler has stopped working because it thinks the internal pipe temperature is dangerously high due to a faulty electrical sensor.
Your boiler has lost communication with its main heat sensor, meaning it cannot monitor water temperature and has stopped running as a safety precaution.
Your boiler has stopped working because an internal sensor that monitors heat levels has developed a fault and can no longer send an accurate reading.
Your boiler has lost communication with its internal temperature sensor, causing the system to stop working as a safety precaution.
Your boiler is failing to detect that a flame has been lit, which is causing the system to shut down for safety.
Your boiler's control system is unable to communicate with the part that regulates gas flow, which has caused the unit to shut down for safety.
Your boiler has lost communication with the internal gas control system, meaning it cannot safely regulate the fuel it needs to stay lit.
Your boiler has lost its flame while running and cannot stay lit, meaning your heating and hot water will likely stop working.
Your boiler’s internal configuration chip is incorrect or faulty, which means the main control board cannot identify which model it is supposed to be operating.
Your boiler is failing to detect a flame when it tries to start, meaning your heating and hot water will likely stop working.
Your boiler is struggling to detect a flame and is failing to stay alight during the start-up process.
Your boiler has detected an unusual temperature reading because a sensor is not communicating properly with the main control system.
Your boiler is struggling to move water through its internal heater fast enough, which is causing it to shut down to prevent overheating.
Your boiler has detected that the water inside it is getting too hot and has shut down as a safety precaution.
Your boiler is overheating because water isn't moving through the internal heat exchanger fast enough to cool it down.
Your boiler has detected that water is heating up too quickly or unevenly, causing it to shut down for safety.
Your boiler has detected that the water pressure in your heating pipes is falling much faster than normal, usually due to a significant leak.
Your boiler has detected that the water pressure in your central heating system is too low to operate correctly.
Your boiler has detected that there is not enough water circulating through the system, which could be caused by a leak or a pump that has stopped working.
Your boiler's water pump is either trapped with an air bubble or is physically jammed, preventing water from circulating properly to heat your home.
Your boiler has detected an electrical fault with the sensor that monitors exhaust gases, causing the system to shut down for safety.
Your boiler's hot water sensor is not working correctly, meaning your taps might not get hot or the temperature will be inconsistent.
Your boiler has lost its connection to the external heating controls, meaning the thermostat and the boiler are no longer talking to each other.
Your boiler is not receiving a stable or correct level of electricity, causing it to stop running to protect its internal circuits.
Your boiler has lost its identity because a small memory chip inside is either missing or has a bad connection to the main control board.
Your boiler’s internal computer has encountered a critical electronic failure and can no longer control the heating process safely.
Your boiler has detected that the air circulation needed for the flame to burn safely has been interrupted while it was running.
Your boiler's internal computer has suffered a serious electronic failure and can no longer control the heating process safely.
Your boiler has noticed an unusual airflow issue during its daily self-check, which prevents it from firing up safely.
Your boiler has detected that the internal fan, which safely clears waste gases, is spinning too slowly or has lost its electrical connection.
Your boiler has stopped working because the fan is spinning at the wrong speed, preventing the system from safely clearing exhaust fumes.
Your boiler's fan is not spinning fast enough to safely clear away waste gases, causing the system to shut down for safety.
Your boiler has detected that the fan responsible for clearing exhaust gases is not spinning, which has caused the system to shut down for safety.
Your boiler has stopped working because the internal fan isn't spinning fast enough to safely clear away exhaust gases.
Your boiler has stopped working because the fan that helps remove waste gases has unexpectedly quit while the unit was running.
Your boiler is having trouble communicating with the temperature sensor located on the outside of your house, which helps it run more efficiently based on the weather.
Your boiler has stopped working because the water pressure inside the system has dropped below the minimum level needed to operate.
Your boiler has stopped working because the central heating pump is not moving water through the system correctly.
Your boiler has lost the ability to monitor the temperature of the water returning to the unit, likely because a internal sensor has failed or gotten damp.
Your boiler has stopped working because it can no longer communicate with the internal sensor that monitors the temperature of the water returning to the unit.
An external safety device or internal safety link has triggered, causing the boiler to shut down to prevent damage.
Your boiler is shutting down because it is heating up much faster than it should, which usually means water isn't moving through the system properly.
Your boiler is overheating because water is not moving through the system quickly enough to be cooled down.
Your boiler has shut down because it thinks the internal water temperature has become dangerously overheated.
Your boiler is overheating because the water inside it is heating up much faster than it can be circulated around your home.
Your boiler's internal thermometer that measures the temperature of the water heading to your radiators has developed a fault and is providing an incorrect reading.
Your boiler's internal thermometer has developed an electrical fault and can no longer safely monitor the temperature of the water leaving the unit.
Your boiler has lost connection with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot safely regulate heat.
Your boiler has lost communication with the internal thermometer that monitors water temperature, causing the system to shut down for safety.
Your boiler has detected an electrical fault with the internal sensor that monitors water temperature, causing the system to shut down for safety.
Your boiler has stopped working because it cannot communicate with the sensor that monitors the temperature of the water leaving the unit.
Your boiler has detected that the water inside is getting too hot and has shut itself down as a safety precaution.
Your boiler has shut down because a sensor has detected that the water inside is getting too hot, or there is a problem with the circulation or pressure preventing safe cooling.
Your boiler has shut down because it detected that the exhaust gases are too hot, which is a safety mechanism to prevent damage or dangerous fumes.
Your boiler has shut down because a safety sensor has detected that the internal water temperature is too high or the sensor itself has failed.
Your boiler has shut down because a safety sensor has detected that the water inside has become dangerously hot or the sensor itself has developed a fault.
Your boiler has switched itself off because it has detected an unsafe level of heat within the internal flue system.
Your boiler has shut down because it has detected that the water inside it has become too hot.
Your boiler has shut down because its internal safety system has detected that the water inside has become dangerously hot.
Your boiler has sensed that the water returning to the unit is much too hot, causing it to shut down to prevent damage to the internal components.
Your boiler has shut down because a safety sensor has detected that it is losing connection or overheating, preventing potential damage.
Your boiler has stopped working because it cannot light the burner, which is usually caused by a problem with the gas supply or the ignition system within the unit.
Your boiler is not detecting a pilot light or flame, which means it has stopped working as a safety precaution.
Your boiler was working but the flame has unexpectedly gone out, causing the system to shut down for safety.
Your boiler has lost its connection to the gas valve, meaning it cannot light the flame to provide heating or hot water.
Your boiler has lost its flame or cannot detect it because the internal control brain has encountered a software or electrical glitch.
Your boiler is trying to light itself but the ignition burner is staying on for too long without successful combustion.
Your boiler's internal computer has encountered a memory or electrical glitch and cannot safely start the burner.
Your boiler is struggling to move water around the system properly, causing it to run at a very low power to prevent overheating.
Your boiler’s internal computer has developed a fault and can no longer communicate with the heating system, causing the boiler to shut down.
Your boiler's computer is having trouble communicating with its internal components, causing the system to shut down for safety.
Your boiler’s internal computer has encountered a critical communication error and can no longer process instructions safely.
Your boiler has detected an internal electrical fault with the gas control system, meaning it cannot safely ignite to provide heating or hot water.
Your boiler's main internal computer has developed a communication fault and cannot operate the heating or hot water safely.
Your boiler’s internal computer has developed a fault or lost connection, meaning the system cannot safely manage the heating process.
Your boiler’s internal computer has developed a fault and can no longer communicate with the heating system, causing the boiler to stop working.
Your boiler's main internal computer has developed a communication fault or an electronic failure, meaning it can no longer control the heating process safely.
Your boiler's internal computer has encountered a critical electronic failure and cannot safely operate your heating or hot water.
Your boiler's internal computer is detecting a communication error with its temperature sensors and cannot safely confirm the water temperature.
Your boiler's main internal computer has developed a serious internal error and can no longer safely operate the appliance.
Your boiler's internal computer has developed a fault or is not communicating properly with its main control unit, preventing the system from starting.
Your boiler's internal computer has encountered a critical communication error and can no longer safely control the burner.
Your boiler’s internal computer has encountered a critical error, meaning the main control system is unable to communicate with its internal components.
Your boiler's internal computer or its communication chip has suffered a technical failure and can no longer control the heating process.
Your boiler’s internal computer has developed a fault and can no longer communicate with the heating components, causing the system to shut down for safety.
Your boiler thinks a flame is present even when it should be off, causing it to lock down for safety.
Your boiler thinks a flame is present even though it hasn't actually started the ignition process yet.
Your boiler has experienced a temporary interruption to its electrical supply and needs to be reset to resume normal operation.
Your boiler is still detecting a flame even though it has tried to turn the gas supply off, which is a significant safety concern.
Your boiler thinks a flame is still burning even though it has been told to switch off, which is causing the system to shut down for safety.
Your boiler has shut down because its internal safety checks detected that a gas valve isn't closing properly, which could lead to a small amount of gas escaping into the unit.
Your boiler has detected a potential internal gas leak during its safety startup check and has shut down to keep you safe.
Your boiler is in a temporary 'wait' mode because the reset button was held down for too long or pressed by mistake.
Your boiler has lost its connection to the main electricity supply or has experienced a sudden power interruption.
Your boiler has detected that there is not enough water pressure in the system to operate properly, which is preventing it from heating your radiators or providing hot water.
Your boiler is repeatedly restarting itself due to a recurring internal fault, meaning it cannot provide reliable heating or hot water.
Your boiler is currently sitting in standby mode because it hasn't received a signal from your thermostat or programmer to start heating.
Your boiler is working normally and is currently heating your home as requested by your thermostat.
Your boiler is heating up too quickly and has shut down to prevent overheating, likely because the water isn't flowing through the system properly.
Your boiler appears to have lost all electrical power, meaning the display is blank and the unit will not respond.
Your boiler is currently resetting itself or stuck in a restart sequence, which usually happens after a fault has been detected or the reset button has been held down.
Your boiler is currently testing its ability to create a spark to light the burner.
Your boiler is having trouble starting up because it cannot confirm that the internal fan is spinning at the right speed to safely clear away exhaust fumes.
Your boiler is checking if the pump is working correctly to move water through the system, but it has not detected the required flow.
Your boiler is having trouble switching between your heating and hot water functions during its internal safety check.
Your boiler has detected an internal safety check failure related to how it monitors the flame, meaning it cannot start up safely.
BoilerFaultCodes