56 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
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The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.
| GC number | Appliance (register name) | Produced |
|---|---|---|
| 47-709-17 | NCB300 NCB300-30K | 2024–present |
| 47-709-17 | NCB300 NCB300-30K | 2024–present |
Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.
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Your boiler has detected an internal communication error and has safely shut itself down as a precaution.
Your boiler has failed to light the flame properly and has stopped attempting to heat your home or water for safety reasons.
Your boiler has detected a false flame signal, meaning the system thinks the burner is lit when it should be turned off.
Your boiler has temporarily sensed a flame when it shouldn't be there, but it has safely cleared itself so your heating should still be working normally.
Your boiler has detected that it is not receiving enough water flow to operate safely or effectively.
Your boiler has temporarily stopped working because it detected that the burner flame went out while trying to run.
Your boiler has detected an issue related to the flow of water inside the unit, which has caused it to stop working to protect itself from potential overheating.
Your boiler has temporarily shut down because a safety sensor detected that it got too hot inside.
Your boiler has failed to ignite or has lost the flame during operation because it is not receiving a consistent supply of gas.
Your boiler has detected dangerously high temperatures in the exhaust flue and safely shut itself down to prevent damage.
Your boiler has detected an issue with the air supply or exhaust ventilation that prevents it from firing up safely.
Your boiler has detected an issue with the sensors that monitor the water flow, which is preventing it from firing up correctly.
Your boiler has detected a problem with the internal fan that controls the airflow needed to operate safely.
Your boiler has detected an issue with the airflow or exhaust system, meaning it cannot operate safely and has shut itself down.
Your boiler has detected that the internal fan is not spinning at the correct speed to safely push out exhaust gases.
Your boiler has detected an issue with the air flowing through the flue system, causing it to shut down for safety.
Your boiler has detected an issue with the air flowing through the system, preventing it from starting safely.
Your boiler has detected an issue with the sensor that tracks the flow of water, which is preventing the system from operating correctly.
Your boiler has detected an internal communication failure between its main control boards, which prevents it from operating correctly.
Your boiler has detected a communication error between its internal parts, meaning it has safely shut down to prevent incorrect operation.
Your boiler has temporarily stopped working because it cannot safely ignite or maintain a flame.
Your boiler has detected an issue with the internal air or exhaust system that is preventing it from operating safely.
Your boiler is having difficulty communicating with its internal control system, which has caused it to stop working to avoid potential damage.
Your boiler has detected an issue with the water flow or circulation sensor, which is preventing it from heating your home or water correctly.
Your boiler has detected a communication error between its main computer and the internal circuit board, which effectively shuts down the system to prevent incorrect operation.
Your boiler has detected that it is getting too hot and has automatically shut down to prevent damage to its internal parts.
Your boiler has failed to ignite or keep a flame lit, meaning it has safely shut down and stopped producing heating and hot water.
Your boiler has failed to ignite or stay lit, meaning your heating and hot water have temporarily stopped working.
Your boiler has failed to ignite or lost its flame, meaning it has safely shut down and stopped producing heating and hot water.
Your boiler has temporarily stopped working because it has detected dangerously high temperatures inside the main heat exchanger.
Your boiler has detected an issue with the main heat exchanger, which usually requires a qualified engineer to inspect and resolve safely.
Your boiler has detected that it is running much hotter than it should be and has switched itself off to prevent damage.
Your boiler has temporarily stopped working because it has detected that the internal water temperature has become too hot.
Your boiler has detected an issue with its temperature sensors or main heat exchanger, so it has safely shut down to prevent overheating.
Your boiler has stopped working because the internal fan that pushes out harmful exhaust gases is not running properly.
Your boiler has stopped working because the internal fan that safely pushes waste gases outside is not spinning properly.
Your boiler is temporarily unable to accurately measure its own temperature, so it has safely shut down to prevent overheating.
Your boiler has temporarily stopped working because it is getting incorrect temperature readings from one of its internal sensors.
Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low.
Your boiler is struggling to monitor the water pressure in your heating system, so it has safely shut down to prevent potential damage.
Your boiler is struggling to accurately read the water pressure in your system, which prevents it from operating safely.
Your boiler is temporarily unable to register the correct water pressure inside the system, which stops it from running safely.
Your boiler has detected a faulty temperature sensor, which means it cannot accurately measure the heat inside the system and has safely stopped working to prevent damage.
Your boiler is getting confused about how hot the water inside it is because one of its temperature sensors has stopped working properly.
Your boiler is having trouble measuring the flow of water through the system, which typically stops it from providing heating or hot water safely.
Your boiler's main control computer is experiencing an internal electronic fault, preventing the system from operating correctly.
Your boiler’s internal computer has identified an error in how its internal configuration switches are set, meaning it cannot operate safely until these are corrected.
Your boiler's electronic control panel is experiencing a communication fault, which prevents the display from responding or controlling the unit properly.
Your boiler's computer memory has encountered a serious internal error and can no longer process instructions correctly, meaning the unit cannot operate.
Your boiler's internal clock has lost its settings, which usually means the system cannot keep time to manage your heating schedule correctly.
Your boiler's main computer control panel is failing to process instructions correctly, which has caused the system to stop operating for safety reasons.
Your boiler is struggling to read the temperature outside, which means it cannot automatically adjust your heating to compensate for the current weather.
Your boiler's main control panel is failing to communicate with the internal system, which will prevent your heating and hot water from working properly.
Your boiler is having trouble communicating with your wall-mounted thermostat or smart control system, which prevents it from knowing when to turn on your heating.
Your boiler has detected a minor internal software or communication glitch and needs to be restarted to clear the error.
Your boiler has detected that its internal settings do not match the type of gas being supplied to your home, preventing it from firing up safely.
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BoilerFaultCodes