Ideal Isar M30 / M100 Fault codes & diagnostics

25 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas 30 kW 2006-2010 Discontinued

Replaced by: Logic Combi

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25 High

All 25 documented codes

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65 L....8.....

Your boiler has detected a problem with the fan that safely removes exhaust gases, meaning it will not fire up for heating or hot water until it is repaired.

High Engineer only £280-450

Parts commonly replaced

  • Fan Assembly
  • Main PCB
  • Wiring Harness

Related codes

66 H.....1.....

Your boiler has detected a problem with the sensor that monitors the temperature of the water leaving the unit, causing it to shut down as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • Flow Thermistor (NTC Sensor)
  • Wiring Harness
  • Main PCB

Related codes

67 H......F........

Your boiler has detected an electrical fault within the ignition system, preventing it from safely lighting the flame.

High Engineer only £120-350

Parts commonly replaced

  • Flame Sensing Electrode
  • Ignition Lead
  • Printed Circuit Board (PCB)

Related codes

68 H......4.......

Your boiler has detected that a sensor monitoring the temperature of the exhaust gases is not working correctly, causing the system to shut down for safety.

High Engineer only £90-180

Parts commonly replaced

  • Flue Thermistor (NTC Sensor)
  • Wiring harness connecting to the sensor

Related codes

69 H......n........

Your boiler has detected an electrical wiring issue where the live and neutral connections are reversed, preventing it from starting for safety reasons.

High Engineer only £80-160

Parts commonly replaced

  • External electrical wiring
  • Printed Circuit Board (PCB)

Related codes

84 L....8.....

Your boiler is unable to safely move air through its system, so it has shut down to prevent any unsafe conditions.

High Engineer only £200-350

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • PCB

Related codes

85 H.....1.....

Your boiler has lost the ability to accurately measure the water temperature, so it has shut down to prevent overheating.

High Engineer only £150-250

Parts commonly replaced

  • NTC thermistor
  • Wiring harness
86 H.....2.....

Your boiler is having trouble measuring the temperature of the water returning to it, which causes it to stop working as a safety precaution.

High Engineer only £150-250

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness

Related codes

87 H.....3.....

Your boiler is struggling to accurately measure the temperature of the water used for your taps and shower, which will likely prevent you from getting hot water.

High Engineer only £120-200

Parts commonly replaced

  • DHW NTC Sensor
  • Wiring harness

Related codes

88 H......4.......

Your boiler has detected that the temperature monitoring system for the exhaust gases is not reading correctly, which means the boiler will stop working to ensure safety.

High Engineer only £150-250

Parts commonly replaced

  • Flue temperature sensor
  • Wiring harness
Showing 11–20 of 25
89 H......F........

Your boiler has detected an issue with the flame during operation, causing it to shut down for safety.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Flame rectification probe
  • Printed Circuit Board

Related codes

90 H......n........

Your boiler's electrical power supply has been connected with the live and neutral wires swapped, which is preventing the system from detecting the flame safely.

High Engineer only £100-200

Parts commonly replaced

  • Electrical spur wiring
  • PCB
H 1

Your boiler's temperature sensor is reporting an inconsistent or faulty reading, causing the system to stop working as a safety precaution.

High Engineer only £120-220

Parts commonly replaced

  • NTC Thermistor
  • Wiring Harness

Related codes

H 2

Your boiler has detected a serious internal system error that requires a professional engineer to investigate.

High Engineer only £150-300

Parts commonly replaced

  • Main printed circuit board (PCB)
  • Wiring harness
H 3

Your boiler has detected an internal communication error and has safely shut itself down as a precaution.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (Main PCB)
  • Wiring Harness

Related codes

H 4

Your boiler has detected a critical internal error that prevents it from starting until a qualified heating engineer resets or repairs the system.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
H E

Your boiler's main control unit has identified an internal electronic error and has shut down for safety to prevent unpredictable system behaviour.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

H F

Your boiler has detected a communication breakdown between its internal computer and the main control board, preventing it from functioning correctly.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

H n

Your boiler has detected a serious communication error between its internal parts and has automatically shut down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Main control PCB
  • Wiring harness

Related codes

L 8

Your boiler has detected an issue with the internal air circulation system, meaning it cannot safely clear waste gases and has shut down to prevent risk.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Wiring harness
  • Printed Circuit Board
Showing 21–25 of 25
L A

Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage or safety issues.

High Engineer only £120-250

Parts commonly replaced

  • Overheat Thermostat
  • NTC Sensor
  • Pump
  • Heat Exchanger

Related codes

L E

Your boiler's main computer control panel has detected an internal error, which means the system has safely shut down to prevent damage.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

L F

Your boiler is failing to light the flame or keep it running, which means it has safely shut itself down to prevent gas from building up.

High Engineer only £150-300

Parts commonly replaced

  • Ignition Electrode
  • Flame Rectification Probe
  • Gas Valve

Related codes

L-A

Your boiler has safety-shut itself down because it detected that the water inside has become dangerously hot.

High Engineer only £120-250

Parts commonly replaced

  • Pump
  • Heat exchanger
  • Overheat thermostat

Related codes

L-F

Your boiler is failing to ignite the internal flame, which means it cannot produce any hot water or heating.

High Engineer only £150-300

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe

Related codes