Ideal I2 Combi 24 Fault codes & diagnostics

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

Combi Natural Gas 2019-present
GC Number 47-349-74
Download the Ideal I2 Combi 24 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.
16 High 1 Medium 1 Low
Fault codes

All 18 documented codes

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F1

Your boiler has stopped working because the water pressure inside the heating system has dropped too low.

High DIY-safe £80-120

What to check first

  1. Locate the internal filling loop, which is usually a small silver lever or a braided hose under the boiler.
  2. Open the filling valve slowly until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.
  3. Close the valve tightly and check that the fault code disappears.

Parts commonly replaced

  • Pressure sensor
  • Filling loop
  • Pressure relief valve

Related codes

Full explanation for F1
F2

Your boiler is trying to start but keeps failing to keep the flame lit, so it has shut down as a safety precaution.

High Engineer only £150-300

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Condensate trap

Related codes

Full explanation for F2
F2 Or Fn Or Ln

Your boiler is failing to stay lit, which means it has safely shut itself down because it cannot consistently produce or hold a flame.

High Engineer only £150-350

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Rectification Probe

Related codes

Full explanation for F2 Or Fn Or Ln
F3

Your boiler has detected an issue with the fan that safely clears exhaust gases, preventing it from starting up for your safety.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for F3
F6

Your boiler is having trouble reading the outdoor temperature, which it uses to help run your heating more efficiently.

Low DIY-safe £90-180

What to check first

  1. Check the external sensor on the outside of your house for any obvious damage or loose wires
  2. Turn the boiler power off and back on to see if the fault clears
  3. Ensure there is no debris or ice covering the outdoor sensor

Parts commonly replaced

  • Outdoor weather compensation sensor
  • External sensor wiring
Full explanation for F6
F7

Your boiler is struggling to operate because the electricity supply from your home is too weak or unstable.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for F7
F8/ L8

Your boiler has detected a software or configuration error in its internal computer, which has caused it to shut down for safety reasons.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Interface Module

Related codes

Full explanation for F8/ L8
F8/L8

Your boiler has detected a software or configuration error in its internal computer, which has caused it to shut down for safety reasons.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Interface Module

Related codes

Full explanation for F8/L8
F9/ L9

Your boiler's main control computer is experiencing a critical error and is unable to communicate properly, meaning your heating and hot water will not work.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for F9/ L9
F9/L9

Your boiler's main control computer is experiencing a critical error and is unable to communicate properly, meaning your heating and hot water will not work.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for F9/L9
FN

Your boiler has lost its flame while trying to run, which means it cannot heat your water or your radiators.

High DIY-safe £120-350

What to check first

  1. Check that your gas supply is turned on at the meter
  2. If you have a prepay meter, check that you have enough credit
  3. Press the Reset button on the boiler display
  4. Ensure your external condensate pipe hasn't frozen in very cold weather

Parts commonly replaced

  • Gas Valve
  • Ignition Electrode
  • Flame Sensing Probe
  • Spark Lead

Related codes

Full explanation for FN
L1

Your boiler has switched itself off because the internal water temperature has become too hot, usually caused by a lack of water flow through the system.

High DIY-safe £120-£350

What to check first

  1. Check that your radiator valves are fully open
  2. Ensure your boiler pressure is between 1 and 1.5 bar on the gauge
  3. Reset the boiler by turning the control knob to 'RE' or pressing the reset button

Parts commonly replaced

  • Circulating pump
  • Thermistor (NTC sensor)
  • Main heat exchanger

Related codes

Full explanation for L1
L2

Your boiler has failed to light several times and has shut down for safety, meaning you currently have no heating or hot water.

High DIY-safe £100-£350

What to check first

  1. Check if your gas supply is active by testing another gas appliance like a hob.
  2. Check if your condensate pipe (the white plastic pipe outside) is frozen or blocked.
  3. Reset the boiler by turning the control knob to 'Reset' and holding for two seconds.

Parts commonly replaced

  • Gas valve
  • Ignition electrode
  • Flame sensing probe
  • Spark generator

Related codes

Full explanation for L2
L4 Or F4

Your boiler's temperature-sensing component is malfunctioning, which prevents it from safely controlling the heat, so it has turned itself off to prevent overheating.

High Engineer only £150-250

Parts commonly replaced

  • Flow NTC Thermistor
  • Wiring harness

Related codes

Full explanation for L4 Or F4
L5 Or F5

Your boiler is struggling because it cannot accurately read the temperature of the water returning to it, so it has safely shut down to prevent overheating.

High Engineer only £120-200

Parts commonly replaced

  • Return thermistor
  • Wiring harness

Related codes

Full explanation for L5 Or F5
L6

Your boiler thinks a flame is burning even though it shouldn't be, causing the system to shut down for safety.

High Engineer only £120-280

Parts commonly replaced

  • Ionisation probe
  • Flame sensing electrode
  • Printed Circuit Board (PCB)

Related codes

Full explanation for L6
LC

Your boiler has temporarily locked itself out for safety because it had to restart five times in a short space of time.

Medium DIY-safe

What to check first

  1. Wait 15 minutes to see if the lockout clears automatically.
  2. Turn the boiler off and on again using the main power switch or reset button to clear the lock.
  3. Check that your home's gas supply is working properly by testing another gas appliance like a hob.

Related codes

Full explanation for LC
LN

Your boiler has lost its flame while running, meaning it is not getting enough gas or the spark is failing to keep the burner lit.

High DIY-safe £100-350

What to check first

  1. Check if your gas meter has credit (if on a prepayment meter)
  2. Check if other gas appliances, like a hob, are working to confirm gas supply
  3. Reset the boiler by turning the mode knob to 'RE' and then back to the desired setting
  4. Ensure the external condensate pipe has not frozen if it is winter

Parts commonly replaced

  • Flame Sensing Electrode
  • Gas Valve
  • Ignition Lead
  • Spark Generator

Related codes

Full explanation for LN
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