21 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 |
|---|---|---|
| 47-920-47 | SD Isotwin Condens F35 E | 2005–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 is failing to light the internal flame needed to produce heat or hot water.
Your boiler is struggling to clear exhaust gases safely, so it has shut down to prevent any risk of fumes entering your home.
Your boiler has detected a problem with the internal airflow or exhaust, so it has safely shut down to prevent harmful gases from building up.
Your boiler is failing to light its burner, which means it cannot produce any heating or hot water for your home.
Your boiler has switched itself off because it has reached an unsafe temperature to protect the internal components from damage.
Your boiler has temporarily stopped working because it cannot accurately measure the temperature of the water flowing through your heating system.
Your boiler has detected a problem with the sensor that monitors hot water temperature, which typically means you will have little or no hot water.
Your boiler's temperature sensor for the hot water storage tank has developed a fault, meaning the system cannot safely monitor or heat your hot water.
Your boiler is struggling to accurately measure the water pressure inside the system, which causes it to shut down to prevent potential damage.
Your boiler has temporarily stopped working because it cannot accurately measure the temperature of the water returning from your radiators.
Your boiler has lost its connection to the control panel or thermostat, meaning it cannot properly receive instructions to heat your home.
Your boiler's internal computer has lost communication with the control panel or display, preventing the system from operating.
Your boiler has temporarily lost communication between its internal control boards, meaning it has safely shut down to prevent incorrect operation.
Your boiler has shut down because the water inside the central heating system has reached an unsafely high temperature.
Your boiler is temporarily locked out because it still senses a flame burning even after the heating has switched off.
Your boiler has stopped working because the electrical power coming from your home's mains supply is too low for it to run safely.
Your boiler's digital display or control panel is having communication issues, which means the machine cannot receive your instructions on how to run.
Your boiler has temporarily stopped working because it has lost the electronic signal from the sensor that monitors the temperature of the water used for your radiators.
Your boiler has stopped working because the internal computer system has detected a software communication error between its main parts.
Your boiler has detected that water isn't flowing through the system properly, which has caused it to shut down to prevent overheating.
Your boiler has detected that the water is heating up or cooling down much faster than it should, indicating a problem with the internal circulation of water.
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BoilerFaultCodes