151 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Greenstar Highflow
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 error with its electronic brain or air flow system and has locked itself for safety.
Your boiler has been left in a testing mode used by engineers and needs to be switched back to its normal operating setting.
Your boiler has been left in a manual testing mode after a recent service, preventing it from operating at its normal settings.
Your boiler's internal computer parts do not recognise each other and cannot communicate correctly, causing the system to stop working.
Your boiler's internal computer module does not match the main control board, preventing the system from starting up.
Your boiler has lost its connection to its internal memory chip, meaning it cannot properly identify itself or control the heating process.
Your boiler is working correctly and is simply letting you know that it is currently busy heating your radiators.
Your boiler is not currently experiencing a fault; it is simply indicating that it is firing up to provide central heating to your home.
Your boiler is simply notifying you that it is currently busy heating your hot water.
Your boiler is currently busy heating your hot water tank and is operating exactly as it should.
Your boiler is working correctly and is simply waiting for a signal from your thermostat to start heating up.
Your boiler is taking a short, temporary break to prevent the burner from turning on and off too frequently, which protects the internal components and saves energy.
Your boiler is currently in a waiting state because there is no immediate demand for heating or hot water.
Your boiler is working correctly but is currently resting because it hasn't been told to turn on by your thermostat or timer.
Your boiler is temporarily pausing because the water inside it is currently hotter than the temperature you have requested.
Your boiler is pausing because the water inside it has become hotter than the temperature you have requested.
Your boiler is currently running at full power for a manual testing sequence and needs to be returned to its normal operating mode.
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 is overheating because the water inside is heating up too fast, often due to a pump failure or a blockage preventing water from moving through the system.
Your boiler has switched itself off because it has detected it is getting too hot, likely due to low water pressure in the system.
Your boiler has recorded that a technician's diagnostic tool was recently plugged in to check the system's error history.
Your boiler is failing to light properly even though it is trying to ignite, which means it cannot provide any heating or hot water until it is repaired.
Your boiler thinks a flame is burning even though it hasn't actually started, which is preventing it from running for safety reasons.
Your boiler's internal computer parts are talking to each other using different languages and need a software update or a compatible replacement part to work together properly.
Your boiler has fired up, but it cannot detect the water getting any warmer, so it has shut down to prevent overheating.
Your boiler has temporarily reduced its power output because it has reached the required temperature and is waiting for the heating system to catch up.
Your boiler is currently running through its internal safety and component checks, which is a normal part of its startup sequence.
Your boiler is simply working hard to increase its power output to meet the heating or hot water demand, which is a normal operation rather than a functional error.
Your boiler is simply performing its normal startup sequence and checking that safety components are ready before lighting the flame.
Your boiler has detected an internal communication error between the control board and the gas valve, causing it to shut down for safety.
Your boiler is busy prioritising your hot water and is waiting for that cycle to finish before it can provide heating for your radiators.
Your boiler is taking a short, programmed break to prevent it from switching on and off too frequently while heating your water.
Your boiler is still detecting a flame even after it has been told to shut off the gas, which is a safety conflict requiring professional attention.
Your boiler has detected an unstable electrical supply or an internal fault with its control board, meaning it cannot operate safely.
Your boiler is not receiving a steady or strong enough supply of electricity from your home to operate safely.
Your boiler's internal computer chips are not communicating correctly because the replacement part fitted is incompatible with the main control board.
Your boiler’s internal computer chip is not communicating correctly with the main control board, meaning the system cannot identify which model it is meant to be.
Your boiler's temperature sensors are detecting an inconsistency, likely due to a faulty sensor or a wiring issue, which is preventing the system from heating effectively.
Your boiler's internal computer system has lost communication with its smart controls or sensors due to a wiring issue or a blown fuse.
Your boiler has detected that the water pressure is too low for it to operate safely and simply needs more water added to the system.
Your boiler's hot water sensor isn't communicating with the system, which means it cannot safely or accurately heat your water.
Your boiler has lost connection with the sensor that monitors your hot water tank, meaning it cannot tell how hot your water is.
Your boiler is having trouble reading the temperature outside, which means it might not adjust its heating levels correctly to match the weather.
Your boiler's internal computer has lost contact with the sensor that monitors water pressure, meaning it cannot safely tell if there is enough water in the system to operate.
Your boiler's outdoor thermometer is not communicating properly, which may cause the heating to run at the wrong temperature for the current weather.
Your boiler has detected an electrical fault with the internal sensor that monitors water temperature, causing the system to shut down as a safety precaution.
Your boiler has lost communication with its internal thermometer, meaning it cannot safely tell how hot the water is getting and has shut down as a precaution.
Your boiler has detected an electrical fault with its main temperature sensor, which has caused the system to shut down for safety.
Your boiler has lost communication with its internal temperature sensor, preventing it from knowing how hot it is and causing the system to shut down for safety.
Your boiler has detected an issue where it cannot confirm if the gas flame is burning correctly, causing the system to shut down for safety.
Your boiler has stopped working because its internal computer has lost communication with the valve that controls the gas supply.
Your boiler has stopped working because the internal control board has lost communication with the gas valve that manages the flame.
Your boiler was running but the flame went out unexpectedly, causing the system to shut down for safety.
Your boiler's internal computer memory chip is missing, broken, or doesn't match the model, preventing the system from starting up.
Your boiler is struggling to light or maintain its burner flame and may require an internal adjustment to the gas mixture.
Your boiler is failing to detect a flame when it tries to start, which is preventing it from heating your home safely.
Your boiler has detected an unusual temperature reading because a sensor wire is faulty or has come loose, causing the system to shut down for safety.
Your boiler is struggling to push water through the heating system quickly enough to prevent it from overheating.
Your boiler has shut down because the water inside has become too hot, which is usually caused by a blockage or a pump failure preventing heat from moving away from the unit.
Your boiler's water is getting too hot too quickly, causing the system to shut down to prevent damage.
Your boiler has sensed an unusual temperature difference between internal sensors, suggesting that water isn't flowing through the system correctly.
Your boiler has detected that the water pressure in your pipes is dropping much faster than it should, often because of a leak or an issue with the expansion tank.
Your heating system has lost water pressure and likely needs to be topped up to continue working.
Your boiler has detected that there is not enough water circulating, which could be due to a leak or a mechanical issue with the pump.
Your boiler's internal pump is either jammed or struggling to move water because there is air trapped inside the pipes.
Your boiler has detected an electrical fault with the sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.
Your boiler is struggling to accurately measure the temperature of your hot water, which usually means it can't provide reliable heat for your taps and showers.
Your boiler has lost its connection to the external heating controls, meaning it cannot receive the signal to turn on properly.
Your boiler is struggling to operate because it isn't receiving a steady or correct supply of electricity from your home's mains or its internal control chip.
Your boiler's internal computer chip is missing or has lost its connection, meaning the system doesn't know which model it is and cannot operate.
Your boiler's computer brain has encountered an internal software or hardware error and is struggling to communicate with the rest of the system.
Your boiler has switched itself off because it detected that the fan or the air supply has stopped working while it was running.
Your boiler's internal computer has suffered an electrical failure and can no longer control the heating process.
Your boiler has detected that the fan was running or air was moving through the system when it should have been off during its daily safety check.
Your boiler has shut down because a built-in safety fan is not spinning fast enough to clear away exhaust fumes.
Your boiler has detected that the internal fan is spinning at the wrong speed, which means it cannot safely clear exhaust gases and will shut down as a precaution.
Your boiler has stopped working because the internal fan isn't spinning fast enough to safely clear away exhaust fumes.
Your boiler has stopped working because the internal fan, which safely exhausts fumes, is not spinning.
Your boiler's fan is not spinning fast enough to safely clear waste gases, which has caused the system to shut down for safety.
Your boiler has shut down because the internal fan, which safely exhausts gases, has stopped spinning while the unit was running.
Your boiler has lost communication with the outdoor temperature sensor, which means the system cannot automatically adjust its efficiency 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 detected that the internal pump is not moving water correctly through the system.
Your boiler has detected a problem with the sensor that monitors water returning to the unit, likely due to moisture or a component failure, causing the system to stop working.
Your boiler has lost its connection to the sensor that monitors water returning from your radiators, causing the system to stop working as a safety precaution.
An external safety device or thermostat has disconnected, telling the boiler to stop running for protection.
Your boiler is shutting down because it is heating up much faster than it should, which usually means the water isn't moving through the system properly.
Your boiler has detected that the water is heating up too quickly or isn't circulating properly, causing it to shut down to prevent overheating.
Your boiler has detected that the water returning to the unit is dangerously hot, causing it to shut down for safety.
Your boiler is heating up too quickly and has shut down to prevent overheating, likely because water isn't moving through the system properly.
Your boiler has detected a fault with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot safely regulate heat.
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 the internal connection to its main temperature sensor has been lost or broken.
Your boiler has lost its connection to the sensor that monitors water temperature, causing the system to stop working 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 lost its connection to the sensor that measures the temperature of the water leaving the unit, so it has stopped heating to prevent damage.
Your boiler has shut down because the internal water temperature has become dangerously hot, likely due to a circulation problem.
Your boiler has sensed that it is becoming dangerously hot and has shut itself down for safety.
Your boiler has shut down because it detected that the exhaust gases are getting too hot, which is a safety measure to prevent damage or dangerous fumes.
Your boiler has shut down because it has detected an unsafe internal temperature or a faulty sensor, preventing the system from overheating.
Your boiler has shut down because it has detected an unsafe level of overheating or a critical electrical fault within its internal safety sensors.
Your boiler has shut down because a safety sensor detected that the internal gases have become too hot.
Your boiler has shut down because the water inside it has become too hot and reached an unsafe temperature.
Your boiler has shut down because it has detected internal temperatures that are too high, often caused by poor water circulation or a blockage.
Your boiler has sensed that the water returning to the unit is much too hot and has shut itself down as a safety precaution.
Your boiler has shut down because a temperature sensor in the exhaust pipe has lost its electrical connection.
Your boiler has tried to light several times but has failed to detect a flame, meaning it has locked itself out for safety.
Your boiler is failing to light or is losing its flame while running, which means your heating and hot water have stopped working.
Your boiler was running but the flame went out unexpectedly, causing the system to shut down for safety.
Your boiler has lost its connection to the gas valve, meaning it cannot light the burner to provide heat or hot water.
Your boiler's computer module has encountered an internal error and has stopped the heating to protect the system.
Your boiler is trying to light itself but failing to sense a flame, causing the ignition system to run for too long before shutting down for safety.
Your boiler's internal computer has encountered a critical error and can no longer safely control the flame, causing the system to shut down.
Your boiler is struggling to move water through the system efficiently, causing it to slow down to prevent overheating.
Your boiler's internal computer or control unit has suffered an electrical failure and can no longer manage the heating process.
Your boiler's internal computer is having trouble communicating with its electrical components, meaning it cannot safely start the ignition process.
Your boiler has experienced a computer software error or a temporary electrical glitch in its main control board.
Your boiler has detected an internal communication failure between the control system and the gas valve, meaning it cannot ignite safely to provide heat.
Your boiler's main internal computer has developed a serious fault and cannot communicate with the system to start the heating.
Your boiler’s internal computer has developed a fault and can no longer communicate with the heating system, meaning it will not fire up.
Your boiler's internal computer or its memory chip has developed a fault and can no longer communicate correctly with the system.
Your boiler's internal computer has developed a fault and can no longer communicate with the heating system.
Your boiler’s internal computer has developed a fault or is not communicating properly with the sensors, meaning it cannot safely command the boiler to fire up.
Your boiler's internal computer has detected a problem with its electronic sensors and cannot safely confirm if it is working correctly.
Your boiler's internal computer has developed a serious communication error and cannot safely operate the burner.
Your boiler's internal computer has developed a fault or is disconnected, meaning the system cannot safely manage the heating process.
Your boiler's internal computer has developed a communication fault and cannot safely light the burner.
Your boiler's internal computer brain is failing to communicate properly, meaning the system cannot start or run safely.
Your boiler's internal computer has developed a fault and can no longer control the heating process safely.
Your boiler's internal computer or its connection has developed a fault, preventing the system from starting or running safely.
Your boiler thinks it sees a flame even though it should be turned off, which is a safety conflict that prevents it from starting up.
Your boiler thinks a flame is present even though it hasn't actually started the ignition process yet, which is a safety conflict that prevents it from running.
Your boiler has detected a temporary loss of electricity and simply needs to be restarted into its normal routine.
Your boiler is still detecting a flame even though it has tried to turn the gas off, which is a serious safety concern.
Your boiler thinks it still sees a flame even though it has commanded the burner to turn off.
Your boiler has detected a potential internal gas leak or a fault with the safety valve that controls the fuel supply.
Your boiler has detected a potential internal gas leak during its safety startup checks and has shut down to keep you safe.
Your boiler has stopped because the reset button was pressed accidentally or for too long, and it just needs a quick restart to clear the error.
Your boiler has experienced a sudden loss of electrical power or a significant voltage drop, causing it to shut down for safety.
Your boiler has detected that the water pressure is too low, preventing it from heating your radiators or providing hot water effectively.
Your boiler has encountered a system error that is causing it to restart itself repeatedly to try and clear the fault.
Your boiler is currently idle because it hasn't received a signal from your thermostat or programmer to start heating.
Your boiler is working normally and is currently heating up to meet the temperature set on your thermostat.
Your boiler is heating up too quickly and has shut itself down to prevent damage, likely because water isn't flowing through the pipes fast enough.
Your boiler appears to have no electrical power, meaning it won't respond or show any signs of life.
Your boiler is currently going through a restart process, which is often its way of trying to clear a temporary error.
Your boiler is currently attempting to light the burner but is stuck checking the spark that starts the flame.
Your boiler is unable to start because it cannot confirm the fan is spinning correctly to clear waste gases.
Your boiler is checking that the pump is moving water through the system correctly, but it has hit a snag during this test.
Your boiler is struggling to direct heat between your radiators and your hot water tank because a motorized internal valve has failed an automatic test.
Your boiler has failed a safety check related to how it detects the flame, meaning it cannot start up for heating or hot water.
BoilerFaultCodes