Ideal Logic COMBI2 C30 Fault codes & diagnostics

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

Combi Natural Gas 2022-present
GC Number 47-349-94
Download the Ideal Logic COMBI2 C30 manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
11 High 1 Medium 1 Low

All 13 documented codes

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F 0C

Your boiler's hot water sensor is not working correctly, meaning your taps might not get hot or the temperature could be inconsistent.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW Thermistor (NTC sensor)
  • Wiring harness connecting to the sensor

Related codes

F 01

Your boiler has detected that there is not enough water in the system to operate safely, causing it to shut down temporarily.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.
  2. Slowly open the small tap(s) on the filling loop to allow water into the system.
  3. Watch the pressure gauge and close the taps once it reaches 1.5 bar, then restart the boiler.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

F 02

Your boiler has stopped working because the flame inside went out and could not be successfully restarted.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Condensate trap

Related codes

F 03

Your boiler has detected that the internal fan is not working correctly, which prevents it from safely venting gases, so it has shut down to protect your home.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • PCB

Related codes

F 04

Your boiler's temperature sensor is providing incorrect information, causing the system to stop working as a safety precaution since it cannot accurately regulate how hot the water is.

High Engineer only £120-200

Parts commonly replaced

  • Flow thermistor
  • Wiring harness

Related codes

F 05 OR L 05

Your boiler has stopped working because a sensor that measures the temperature of the water returning to the system is failing to send a signal, causing the boiler to shut down as a precaution.

High Engineer only £120-200

Parts commonly replaced

  • Return thermistor sensor
  • Wiring loom

Related codes

F 06

Your boiler has lost communication with the weather sensor installed outside your home, so it is temporarily running as if it were a standard system without outdoor temperature compensation.

Low Engineer only £120-200

Parts commonly replaced

  • Outside Temperature Sensor
  • Outdoor Sensor Wiring

Related codes

F0U

Your boiler has detected that the water leaving the unit is far too hot compared to the water returning to it, so it has shut down to prevent internal damage.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • System filter
  • Heat exchanger

Related codes

L 0C

Your boiler is repeatedly attempts to start up and failing, causing it to lock itself out for safety after five unsuccessful tries.

High Engineer only £120-£350

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Electrode
  • Gas Valve
  • Fan

Related codes

L 02

Your boiler is failing to light the flame needed to generate heat and has safely shut down to prevent gas buildup.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead

Related codes

L 04

Your boiler has lost the ability to read the temperature of the water flowing through it, so it has safely shut down to prevent overheating.

High Engineer only £120-200

Parts commonly replaced

  • Flow Thermistor/NTC Sensor
  • Wiring Harness

Related codes

L 06

Your boiler thinks a flame is present before the gas has even started flowing, which is a safety conflict that prevents the system from starting.

High Engineer only £120-£350

Parts commonly replaced

  • Ionisation probe
  • Gas valve
  • Main PCB

Related codes

L2

Your boiler has stopped working because it tried to light five times in a row but could not detect a flame to stay on.

High Engineer only £100-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Saturated condensate trap

Related codes

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