17 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Replaced by: Logic HE
The fault code is already on your display
Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →
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 |
|---|---|---|
| 47-348-29 | isar HE35 | 2003–2011 |
| 47-348-30 | isar HE30 | 2003–2011 |
| 47-348-31 | isar HE24 | 2003–2011 |
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Your boiler has lost the ability to accurately measure the temperature of the water returning to it, so it has shut down to prevent potential overheating.
Your boiler is having trouble 'reading' the temperature of your hot water supply, which means it has stopped heating water to prevent the system from getting too hot.
Your boiler has detected that a temperature sensor is not reading correctly, which prevents it from safely igniting or heating your water.
Your boiler is struggling because the electrical supply wires have been connected the wrong way round, preventing the system from detecting a safe flame.
Your boiler has detected an issue with a safety sensor that monitors water levels and temperature within the unit, causing it to shut down to prevent damage.
Your boiler is trying to start but cannot detect that the burner has successfully lit, so it has shut itself down to keep you safe.
Your boiler is failing to start because it is not sensing the correct electrical connection path from your home's power supply.
Your boiler has stopped working because it has detected a specific internal problem, which is indicated by the number or letter flashing after the F symbol.
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Your boiler's internal computer is experiencing a communication fault and cannot control the system correctly.
Your boiler has detected that it is getting dangerously hot and has shut itself down to prevent damage.
Your boiler has detected that it is running much hotter than it should be and has shut itself down to prevent any internal damage.
Your boiler has detected that it is running much hotter than it should be and has switched itself off to prevent internal damage.
Your boiler's internal computer is experiencing a communication error and cannot safely manage the heating process, causing the system to shut down.
Your boiler has switched itself off for safety and is displaying this code alongside another digit to point to a specific problem.
Your boiler has detected that it is becoming dangerously hot and has shut itself down to prevent any internal damage.
Your boiler has become too hot and has shut itself down as a safety precaution to prevent internal damage.
Not faults — these are normal operating states. Tap to expand.
BoilerFaultCodes