156 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: CDi Classic
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 critical internal communication or hardware error and has locked itself out for safety.
Your boiler has been manually set to run at its lowest power level for testing, which prevents it from heating your home normally.
Your boiler has been left in a manual testing mode, usually used by engineers during a service, which is preventing it from running normally.
Your boiler's internal computer parts do not recognise each other and are unable to communicate, preventing the heating from starting.
Your boiler’s internal computer chip is either loose or is the wrong version for this specific model, causing the system to shut down for safety.
Your boiler has developed a communication fault with its internal identity chip, meaning it no longer recognizes its own settings and cannot operate.
Your boiler is simply letting you know that it is currently operating and working to heat your home's radiators.
Your boiler is working normally and is currently running to provide heat for your radiators.
Your boiler is simply indicating that it is currently busy heating your hot water, which is a normal operating status rather than a breakdown.
Your boiler is simply letting you know that it is currently busy heating up water for your taps.
Your boiler is working normally and is simply waiting for a signal from your thermostat to start heating.
Your boiler is taking a brief programmed rest to prevent itself from switching on and off too frequently, which protects the internal components from unnecessary wear.
Your boiler is currently sitting in a normal standby mode because there is no demand for heating or hot water at the moment.
Your boiler is working correctly and is simply waiting for you to turn up the thermostat or run a hot tap to start heating.
Your boiler is temporarily pausing because it has already reached the required temperature and is waiting for the water to cool down slightly before firing up again.
Your boiler has temporarily stopped because the water inside it has become hotter than the temperature you have requested.
Your boiler is currently running in a manual testing mode used by engineers to check emissions, which overrides your normal temperature settings.
Your boiler is currently set to a manual testing mode used by engineers to check emissions and is not experiencing an actual part failure.
Your boiler has detected that the water inside is heating up too fast, causing it to shut down to prevent damage from overheating.
Your boiler has switched itself off because it has detected it is getting too hot, likely because the water pressure is too low.
Your boiler is displaying a status message indicating that a technician's diagnostic tool has recently accessed the system's error history memory.
Your boiler is trying to light, but the internal system is failing to detect a flame, causing the unit to shut down for safety.
Your boiler thinks it sees a flame even though it isn't actually firing, which is preventing it from starting up safely.
Your boiler’s internal computer and control module are not communicating correctly because their software versions do not match.
Your boiler is starting up, but it is turning itself off quickly because it cannot detect your water getting any warmer.
Your boiler is temporarily reducing its output because it has reached its target temperature and is waiting for the system to cool down before firing up fully again.
Your boiler is currently running a self-diagnostic check of its internal parts, which it usually does automatically.
Your boiler is undergoing a standard internal startup self-test as it prepares to heat up.
Your boiler is simply performing its normal startup sequence and testing internal components before the flame ignites.
Your boiler has detected an internal communication error involving the gas control components, meaning it cannot safely ignite.
Your boiler is temporarily paused because it thinks hot water is still being used elsewhere in your home.
Your boiler is temporarily pausing the hot water production to prevent the system from overheating and will restart automatically in a few minutes.
Your boiler is still detecting a flame even though it has tried to shut off the gas supply, which is a safety conflict.
Your boiler has detected an issue with the electrical power supply it is receiving, meaning the electricity frequency is unstable and the system has shut down for protection.
Your boiler has detected that the incoming electricity supply is too weak or unstable to run the system safely.
Your boiler's computer brains are having a communication problem because an incorrect or faulty internal component has been detected.
Your boiler's internal computer chip is either loose or is not the correct one designed for this specific model, preventing the system from running.
Your boiler has detected a problem with a temperature sensor that monitors how water is circulating through the system, which is preventing it from heating up correctly.
Your boiler has lost its internal connection to the smart controls or main computer system, meaning it cannot receive instructions to provide heating or hot water.
Your boiler has detected that the water pressure is too low for it to operate safely and needs to be refilled.
Your boiler is struggling to provide hot water because the internal sensor that monitors water temperature has stopped working or has come loose.
Your boiler is unable to tell how hot your water is because of a faulty or disconnected internal sensor.
Your boiler's outdoor sensor is faulty or has a loose connection, which may affect how efficiently the system manages your heating based on the weather.
Your boiler's internal pressure monitor has stopped communicating correctly with the main controls, which will prevent the heating from running.
Your boiler's outdoor weather sensor is not communicating correctly, which means the system doesn't know how hard it needs to work to heat your home.
Your boiler has detected an electrical fault with its internal thermometer, meaning it cannot safely monitor the water temperature and has stopped working as a precaution.
Your boiler has lost communication with its internal thermometer, which means it cannot tell how hot the water is getting and has stopped working for safety.
Your boiler has detected an electrical fault with an internal temperature sensor, meaning it cannot monitor heat levels safely and has shut down to prevent damage.
Your boiler has stopped working because it cannot communicate with the internal heat sensor and has shut down for safety.
Your boiler has detected an issue with the flame and has shut down as a safety precaution to ensure gas is not being supplied without being burned.
Your boiler's internal control system has lost communication with the gas supply valve, meaning the boiler cannot safely ignite to provide heating or hot water.
Your boiler is struggling to supply the correct amount of gas required to maintain a steady flame, causing the system to shut down for safety.
Your boiler has lost its flame while it was running and cannot stay lit to provide heating or hot water.
Your boiler has an internal configuration part that is either damaged or incompatible, which is preventing the system from running safely.
Your boiler is struggling to detect a flame when starting up, meaning it may fail to provide consistent heating or hot water.
Your boiler is failing to detect a flame after trying to start, which means it will not provide heating or hot water until it is reset or repaired.
Your boiler has stopped working because its internal sensors are sending conflicting information about the water temperature.
Your boiler has detected that water isn't moving through the system fast enough to safely carry heat away, so it has shut down to prevent overheating.
Your boiler has sensed that the water inside is Getting too hot and has shut itself down as a safety precaution.
Your boiler is heating up too quickly and has shut down to prevent damage, usually because water isn't moving through the system properly.
Your boiler has detected that the water temperature is changing too quickly or unevenly between different sensors, causing it to shut down for safety.
Your boiler has detected that the water pressure in your heating system is falling much too quickly, which usually means there is a significant leak or a fault with the pressure sensor.
Your boiler has detected that the water pressure in your heating system is too low to operate safely.
Your boiler has detected that there isn't enough water moving through the system, which is usually caused by a leak or a pump that has stopped working.
Your boiler's internal pump is unable to circulate water because it is either physically jammed or there is too much trapped air inside the system.
Your boiler has detected a faulty connection or a broken sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.
Your boiler's hot water sensor has failed or has a loose connection, meaning the system cannot accurately measure the temperature of the water coming out of your taps.
Your boiler has lost its connection with your external heating controls, meaning it cannot receive instructions on when to turn on or off.
Your boiler is receiving an unstable or incorrect electrical supply, which is preventing it from running safely.
Your boiler is struggling to clear exhaust fumes or draw in fresh air, so it has safely shut down to prevent any risk.
Your boiler's main control board cannot communicate with the internal configuration chip, meaning the system doesn't know which settings to use and has stopped working.
Your boiler's internal computer has encountered an electronic failure and cannot safely operate the heating or hot water.
Your boiler has failed to light the flame properly and has turned itself off for safety, meaning you currently have no heating or hot water.
Your boiler has shut down because it has detected a problem with the fan or the way air is moving through the system while it was running.
Your boiler's internal computer has suffered an electrical failure and can no longer control the heating process safely.
Your boiler has detected a small airflow issue while running its daily safety self-test, often meaning it needs a professional service or a minor part cleaned.
Your boiler has stopped working because the internal fan, which safely clears exhaust gases, isn't spinning fast enough.
Your boiler has stopped working because the fan is spinning at the wrong speed, which means the system cannot safely clear exhaust gases.
Your boiler has stopped working because the internal fan that clears away waste gases is spinning too slowly or is stuck.
Your boiler has stopped working because the fan that clears out exhaust gases is unable to start or run properly.
Your boiler has stopped working because the internal fan isn't spinning fast enough to safely clear away exhaust fumes.
Your boiler has shut down because the internal fan, which safely clears waste gases from the system, has suddenly stopped working while the boiler was running.
Your boiler has lost connection with its outdoor temperature sensor, which means it cannot adjust its settings based on the weather outside.
Your boiler has stopped working because there is not enough water pressure in the system to operate safely.
Your boiler has stopped working because it has detected that the internal pump is not moving water through the system correctly.
Your boiler has detected a problem with the sensor that monitors water returning to the unit, meaning it cannot safely track temperature levels.
Your boiler has stopped working because it has lost a connection with one of its internal heat sensors.
An external safety device or thermostat has signaled the boiler to stop running, often due to an issue like a full condensate pump or a tripped safety switch.
Your boiler is overheating because the water inside it is getting too hot much faster than it should be.
Your boiler is shutting down because it has detected a sudden rise in temperature or a lack of water flow, often caused by a blockage or air trapped in the system.
Your boiler has shut down because it thinks the water returning to the unit is dangerously hot, which usually means water isn't circulating properly.
Your boiler is overheating because the water inside it is heating up much quicker than it can be pumped away.
Your boiler's internal thermometer that measures the temperature of the water leaving the unit has stopped working correctly, causing the system to shut down for safety.
Your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the water flowing to your radiators.
Your boiler has stopped working because it has lost the connection to the internal sensor that monitors the temperature of the water leaving the unit.
Your boiler has stopped working because it can no longer communicate with the internal sensor that monitors the temperature of the water leaving the unit.
Your boiler has detected a fault with the sensor that monitors the water temperature leaving the unit, causing the system to shut down for safety.
Your boiler has lost its connection to the sensor that monitors the water temperature, meaning it cannot safely heat your home or water.
Your boiler has sensed that the water inside is getting too hot and has shut down as a safety precaution.
Your boiler has shut down because it has detected that the water inside is getting too hot or the pressure is incorrect.
Your boiler has detected that the exhaust gases are too hot or a safety sensor has broken, causing the system to shut down for your protection.
Your boiler has detected that it is getting too hot and has shut itself down to prevent damage to its internal parts.
Your boiler has shut down because it has detected an unsafe level of overheating or a serious fault with its primary temperature sensor.
Your boiler has switched itself off because it has detected that the internal gases have become too hot, which is a safety measure to prevent damage.
Your boiler has shut down because it has become too hot internally and needs to cool down for safety.
Your boiler has shut down because it has detected internal temperatures that are too high, meaning it is overheating to protect the system.
Your boiler has sensed that the water returning from your radiators is too hot, causing the system to shut down to prevent damage.
Your boiler has shut down because a safety sensor has detected that the exhaust gases are getting too hot or the sensor itself has lost its electrical connection.
Your boiler is failing to light the gas flame and has locked itself out as a safety precaution.
Your boiler has tried to light several times but cannot detect a stable flame, so it has shut down for safety.
Your boiler has lost its flame while it was running, which means it has safely shut down because it can no longer detect the heat needed to stay on.
Your boiler has lost its connection with the gas valve, meaning it cannot ignite to provide heat or hot water.
Your boiler has failed to ignite several times, likely due to a software or communication error within its internal control system.
Your boiler is trying to start but the internal lighting sequence is taking too long to detect a flame, causing the system to lock out for safety.
Your boiler’s internal computer has encountered a critical error and has stopped the heating process to ensure safety.
Your boiler is slowing itself down because water isn't moving through the system quickly enough to take the heat away.
Your boiler's electronic brains have developed a fault, meaning the system cannot communicate internally and has shut down as a safety precaution.
Your boiler has experienced an internal electrical communication error, meaning it cannot process the signals needed to start up or stay running.
Your boiler's internal computer has encountered a communication fault and can no longer control the heating or hot water safely.
Your boiler has detected an electrical communication problem with the internal gas control system, meaning it cannot safely light the flame to provide heating or hot water.
Your boiler's main internal computer has developed a fault and can no longer control the heating process safely.
Your boiler’s internal computer has encountered a critical communication error and cannot tell the system to heat up.
Your boiler’s internal computer system has detected a fatal electronic failure and can no longer control the heating process safely.
Your boiler’s internal computer brain or its memory card has developed a communication fault and can no longer control the heating process.
Your boiler’s internal computer has encountered a critical error or is not communicating properly, meaning the system cannot run.
Your boiler's internal computer has detected a problem with its electronic sensors and cannot safely confirm the temperature.
Your boiler's main internal computer has developed a serious internal fault and can no longer communicate with the parts that manage the flame.
Your boiler's internal computer brain or its memory chip has developed a fault or is not connected properly, preventing the unit from starting.
Your boiler's internal computer has developed a communication fault and cannot safely light the burner to provide heat.
Your boiler's internal computer brain is having trouble communicating or has failed, meaning the system cannot run safely.
Your boiler's computer system has detected an internal electronic failure and has shut down for safety.
Your boiler's internal computer brain or its memory module has developed a technical fault, preventing the system from operating.
Your boiler thinks it can see a flame when it shouldn't be running, which is a safety precaution that prevents the unit from starting up.
Your boiler thinks a flame is present when there shouldn't be one, so it has locked itself out as a safety precaution.
Your boiler has experienced a temporary interruption in its electric power supply and needs to be reset to resume normal operation.
Your boiler is still detecting a flame even though it should have turned off, which is a safety concern that requires an expert's attention.
Your boiler is still detecting a flame after it was supposed to have turned off, which is a safety conflict causing the system to lock out.
Your boiler has detected a potential internal gas leak or a serious safety issue within its fuel management system and has shut down to keep you safe.
Your boiler has detected a potential internal issue with the gas control system and has shut down for safety purposes.
Your boiler thinks you have accidentally bumped the reset button and is simply waiting for you to confirm the action to restart.
Your boiler has lost its connection to the electrical supply or has detected an issue with the power coming into the unit.
Your boiler has detected that the water pressure in the system is too low, which is preventing it from providing full heating or hot water.
Your boiler is experiencing a critical electronic failure that is causing it to repeatedly restart itself, which prevents it from providing heating or hot water.
Your boiler is currently sitting in standby mode because it hasn't received a signal from your thermostat or timer to turn on.
Your boiler is operating normally and is currently providing heat to your radiators or hot water tank.
Your boiler has stopped working because it cannot detect a flame, likely due to an interruption in your gas supply.
Your boiler is overheating because the water inside it is getting too hot too quickly, usually because it isn't moving through the system properly.
Your boiler has lost power completely and the display screen is blank, meaning it cannot start the heating or hot water process.
Your boiler has detected that the water inside the unit has become dangerously hot and has shut itself down to prevent damage or fire risk.
Your boiler is currently going through a reset process, which usually happens after a fault has occurred or the reset button has been pressed.
Your boiler is struggling to accurately measure the temperature of the water, which means it has stopped heating because it is unsure if it is safe to do so.
Your boiler is currently running a self-diagnostic test to check if the ignition spark is working correctly.
Your boiler is having trouble starting up because it cannot verify that the internal fan is spinning at the correct speed to safely clear exhaust fumes.
Your boiler is checking if the pump is circulating water correctly and has detected a potential blockage or pump failure.
Your boiler is having trouble switching between your heating and hot water because an internal valve is stuck or failing its startup check.
Your boiler's electronic control system is failing to carry out its internal safety checks, preventing the unit from starting safely.
BoilerFaultCodes