6 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 |
|---|---|---|
| 41-592-59 | Ultra 21 Heat 21 | 2017–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 temporarily stopped working because it either got too hot or detected a faulty temperature sensor.
Your boiler has automatically shut down because it has detected an unusually high temperature inside the system.
Your boiler is trying to start up or keep running, but the flame keeps going out.
Your boiler has stopped working because it cannot safely detect airflow through the flue or has lost internal communication.
Your boiler has lost its memory or programming settings, meaning it cannot safely control your heating.
Your boiler is experiencing an unspecified general error indicated by flashing indicator lights, which requires a professional inspection to diagnose safely.
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BoilerFaultCodes