20 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: CSI / CSX Primary range
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Your boiler is struggling to move water around the system, which is causing it to shut down to prevent overheating.
The boiler's internal sensor that monitors water temperature or flow has failed, meaning the system cannot safely regulate heat.
Your boiler's hot water sensor has failed, which means the system cannot accurately heat water for your taps and showers.
Your boiler has detected a problem with the fan that clears exhaust gases, preventing it from starting safely for heating or hot water.
Your boiler is getting too hot inside, which has triggered a safety shutdown to prevent damage to the system.
Your boiler has detected that there is not enough water in the system to operate safely.
Your boiler has shut down because it has detected that the water inside is getting too hot, usually due to a circulation blockage or a pump failure.
Your boiler has too much water in the system, which causes it to shut down for safety.
Your boiler's computer system has encountered a processing glitch and has stopped working to protect itself.
Your boiler has detected that the water returning from your radiators is too hot, which has caused it to shut down for safety.
Your boiler has detected that the exhaust gases are becoming too hot and has shut down as a safety precaution.
Your boiler has detected a problem with the sensor that monitors exhaust gases, and it has shut down as a safety precaution.
Your boiler has detected a problem with the sensor that monitors the temperature of the water returning from your radiators, meaning it may not be able to heat your home effectively.
Your boiler has detected that the water inside the main heating unit has frozen, which is preventing the system from operating to avoid damage.
Your hot water system is getting too hot and has shut down as a safety precaution.
Your boiler is having trouble 'talking' to your smart thermostat or external heater controls, meaning it may not receive instructions to turn on or off.
Your boiler has detected that the water isn't moving through the system correctly, causing a large temperature gap between the pipes.
Your boiler has shut down because there is a confusing difference between the temperatures recorded at its internal sensors, often caused by poor water flow or a sensors reading incorrectly.
Your boiler has detected an unusual temperature difference between the pipes, causing it to shut down to prevent overheating.
Your boiler has detected a problem with the sensor that monitors internal water pressure, meaning it cannot confirm if there is enough water to operate safely.
BoilerFaultCodes