12 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: CB28 Plus
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 is struggling to accurately read its own internal water temperature, which means it has safely shut down to prevent overheating.
Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.
Your boiler has attempted to start several times but has been unable to successfully ignite its internal flame.
Your boiler is failing to light because it cannot detect a flame, meaning you currently have no heating or hot water.
Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.
Your boiler has detected an issue with the ventilation system that clears away exhaust gases, so it has shut itself down to keep your home safe.
Your boiler's temperature sensor is faulty, which means the system cannot accurately read how hot the water is and has stopped working as a safety precaution.
Your boiler has lost the ability to accurately measure the temperature of the hot water it produces, so it has turned off the hot tap function to prevent overheating.
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Your boiler has detected that the internal fan is not operating correctly, which prevents it from safely venting gases, so it has shut down to protect your home.
Your boiler is struggling because it detects a confusing difference in temperature between the water leaving the unit and the water returning to it, so it has shut down to prevent damage.
Your boiler has lost its digital connection to the wall-mounted thermostat or controller, preventing it from receiving instructions to start heating.
BoilerFaultCodes