Ideal INDEPENDENT COMBI2 Fault codes & diagnostics

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

Gas 2022-present

The INDEPENDENT COMBI2 range comes in 2 types

Pick the one you have. The fault codes, GC numbers and manual differ by type.

Each model has its own manual A family spans several manuals, one per model or generation. Pick your model above and its page has the manual its fault codes were read from.

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 26 High 1 Medium 1 Low

All 29 documented codes

Tap any card for details

dU

Your boiler is confused about whether to send hot water to your taps or your radiators because an internal valve is stuck in the middle.

High Engineer only £150-300 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Diverter valve cartridge
  • Diverter valve motor
F 0C

Your boiler has detected a problem with the sensor that monitors the temperature of your hot water, which may prevent it from heating up correctly.

High Engineer only £90-160 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • DHW Thermistor (NTC Sensor)
  • Wiring harness / Connector

Related codes

F 0t

Your boiler is failing to communicate with your wall-mounted thermostat, which is preventing it from knowing when to turn the heating on.

Medium DIY-safe £90-200 Shared across the INDEPENDENT COMBI2 range

What to check first

  1. Check if your thermostat requires new batteries and replace them if necessary
  2. Ensure your thermostat is switched on and within signal range of the boiler receiver
  3. Turn the boiler off at the fused spur for 60 seconds and then back on to reset the connection

Parts commonly replaced

  • Room Thermostat
  • Wireless Receiver Unit

Related codes

F 02

Your boiler has lit up but the flame has unexpectedly gone out, causing the system to stop working as a safety precaution.

High Engineer only £150-300 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Ignition electrode
  • Flame rectification probe
  • Gas valve

Related codes

F 03

Your boiler has detected an issue with its internal air extraction system, which is preventing it from safely lighting and operating.

High Engineer only £180-350 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Printed Circuit Board (PCB)
F 04

Your boiler's temperature sensor is providing incorrect readings or has disconnected, so the system has safely shut down to prevent overheating.

High Engineer only £120-220 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Flow Thermistor/NTC Sensor
  • Wiring Harness

Related codes

F 04 or L 04

Your boiler has stopped working because a sensor that measures the water temperature is failing to send a signal, meaning the system cannot safely regulate your heating.

High Engineer only £120-220 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Flow Thermistor
  • Wiring Loom

Related codes

F 05

Your boiler has lost the ability to accurately measure the temperature of the water returning to it, so it has shut down as a precaution to prevent overheating.

High Engineer only £120-220 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Return thermistor sensor
  • 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 it has stopped sending a reliable signal.

High Engineer only £120-200 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Return NTC Sensor
  • Wiring harness

Related codes

F 06

Your boiler is currently unable to communicate with its outdoor weather sensor, which means it cannot automatically adjust your heating based on the outside temperature.

Low Engineer only £100-200 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Outside Air Temperature Sensor
  • Wiring harness

Related codes

Showing 11–20 of 29
F 07

Your boiler has detected that the electricity coming into your home is weaker than it should be, preventing the boiler from functioning reliably.

High Engineer only Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • None - issue is typically external power supply
  • Printed Circuit Board (PCB)
F 09

Your boiler's internal computer is experiencing a critical error and can no longer safely control the system, meaning the boiler will not function until the unit is serviced.

High Engineer only £250-400 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Main PCB

Related codes

F 10

Your boiler is failing to ignite the flame needed to produce heat and hot water because of an internal electrical connection or component issue.

High Engineer only £150-250 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Ignition lead
  • Ignition transformer
  • Ignition electrode

Related codes

F 12

Your boiler has detected that the water pump is stuck and cannot move the water around your heating system properly, which has caused the boiler to switch itself off.

High Engineer only £120-250 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Central Heating Pump
  • Pump Head

Related codes

F 13

Your boiler has detected that the internal mechanism responsible for circulating hot water around your home's radiators and taps has stopped working correctly.

High Engineer only £250-450 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Central heating pump
  • Pump wiring harness
  • Printed Circuit Board (PCB)

Related codes

F 14

Your boiler has detected that the electricity coming into your home is outside the safe operating range, which requires a check from your local power supplier.

High Engineer only Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • PCB
  • Wiring harness

Related codes

F 15

Your boiler has detected that the water pump responsible for circulating heat around your home has stopped working correctly.

High Engineer only £250-450 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Central heating pump
  • Wiring harness

Related codes

F 16

Your boiler has detected an issue with the component that controls the gas supply, meaning it has safely shut down to prevent any unsafe operation.

High Engineer only £180-300 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Gas valve
  • Wiring harness

Related codes

F 17

Your boiler is unable to move hot water around your home because the central pump responsible for circulation has stopped working.

High Engineer only £250-£450 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Circulating pump
  • Pump wiring harness
F0U

Your boiler has detected that the water inside is getting much too hot compared to the water returning, which usually points to a blockage in the system or a circulation problem.

High Engineer only £150-350 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Circulating pump
  • Automatic bypass valve
  • Plate heat exchanger

Related codes

Showing 21–29 of 29
F01

Your boiler has locked out due to low water pressure in the system, meaning it has temporarily stopped working to protect itself.

High DIY-safe Shared across the INDEPENDENT COMBI2 range

What to check first

  1. Locate the filling loop underneath your boiler.
  2. Open the valves slowly until the pressure gauge on the front of the boiler rises to between 1.0 and 1.5 bar.
  3. Close the valves firmly and press the reset button on the boiler.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
  • Automatic air vent

Related codes

L 0C

Your boiler has temporarily locked itself out for safety after failing to start up five times in a row.

High Engineer only £150-350 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board (PCB)

Related codes

L 0d

Your boiler has stopped working because it cannot safely get rid of its exhaust gases or clear its wastewater.

High Engineer only £90-180 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Condensate trap
  • Air pressure switch
  • Flue terminal

Related codes

L 02

Your boiler has failed to light the flame, so it has safely shut itself down to prevent any unburned gas from building up.

High Engineer only £120-250 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Ignition Lead

Related codes

L 04

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

High Engineer only £150-250 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Flow Thermistor/NTC Sensor
  • Wiring Harness

Related codes

L 05

Your boiler is currently unable to read the temperature of the water returning to it, so it has shut down to prevent potential damage.

High Engineer only £120-200 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Return thermistor
  • Wiring harness

Related codes

L 06

Your boiler has detected a flame signal when it shouldn't have, which indicates an internal safety sensor issue that prevents the boiler from starting.

Emergency Engineer only £150-300 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Flame rectification probe
  • Printed circuit board (PCB)
  • Gas valve

Related codes

L01

Your boiler has stopped working safely and is locked out, but the specific reason is shown by the number following the letter 'L' on your display.

High Engineer only £100-250 Shared across the INDEPENDENT COMBI2 range

Parts commonly replaced

  • Ignition Lead
  • Gas Valve
  • Printed Circuit Board

Related codes

L2

Your boiler has tried to light five times in a row and failed, so it has safely locked itself off to prevent a build-up of gas.

High DIY-safe £100-250 Shared across the INDEPENDENT COMBI2 range

What to check first

  1. Check if your gas supply is working by testing another gas appliance like a cooker.
  2. Check your gas prepayment meter to ensure you have credit if applicable.
  3. Press the reset button on your boiler for up to 5 seconds to try restarting the ignition process.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

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