Ideal INDEPENDENT SYSTEM Fault codes & diagnostics

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

System Gas 2016-present
Choose your boiler type

The INDEPENDENT range comes in 3 types

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

S18 23 codes · 1 GC number s24 23 codes · 1 GC number s30 23 codes · 1 GC number
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.
19 High 1 Low
Just want the most common Ideal INDEPENDENT SYSTEM faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 20 documented codes

Tap any card for details

F1

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

High DIY-safe £80-120 Shared across the INDEPENDENT System range

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 Shared across the INDEPENDENT System range

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Condensate trap

Related codes

Full explanation for F2
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 Shared across the INDEPENDENT System range

Parts commonly replaced

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

Related codes

Full explanation for F3
F4

Your boiler has sensed a problem with its internal temperature sensors or a lack of water movement, causing it to shut down for safety.

High Engineer only £100-£220 Shared across the INDEPENDENT System range

Parts commonly replaced

  • Flow thermistor
  • Return thermistor
  • Main PCB

Related codes

Full explanation for F4
F5

Your boiler has detected a sensor problem that means it cannot accurately measure the temperature of the water returning to the unit, causing it to shut down for safety.

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

Parts commonly replaced

  • Return thermistor (NTC sensor)
  • Wiring harness
  • Main PCB

Related codes

Full explanation for F5
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 Shared across the INDEPENDENT System range

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 not receiving enough electrical power from the grid to operate safely and has shut down as a precaution.

High Engineer only £0-350 Shared across the INDEPENDENT System range

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Voltage Regulator

Related codes

Full explanation for F7
F8

Your boiler's main control board has lost its memory or settings, meaning it no longer knows how to run your specific model of boiler.

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

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Display PCB

Related codes

Full explanation for F8
F9

Your boiler's main electronic brain has lost its programming settings and needs to be reconfigured or replaced.

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

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for F9
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 Shared across the INDEPENDENT System range

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
Showing 11–20 of 20
FU

Your boiler has detected that heat is building up too quickly and cannot circulate around your home, likely due to a blockage or a pump failure.

High DIY-safe £150-£350 Shared across the INDEPENDENT System range

What to check first

  1. Check that the main isolation valves underneath the boiler are fully open
  2. Ensure at least two or three radiators have their valves turned to the maximum setting
  3. Check that the boiler pressure is between 1.0 and 1.5 bar on the gauge

Parts commonly replaced

  • Central heating pump
  • Main heat exchanger
  • Return thermistor

Related codes

Full explanation for FU
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 Shared across the INDEPENDENT System range

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 Shared across the INDEPENDENT System range

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

Your boiler has sensed a problem with its internal temperature sensors or a lack of water movement, causing it to shut down for safety.

High Engineer only £100-£220 Shared across the INDEPENDENT System range

Parts commonly replaced

  • Flow thermistor
  • Return thermistor
  • Main PCB

Related codes

Full explanation for L4
L5

Your boiler has detected a sensor problem that means it cannot accurately measure the temperature of the water returning to the unit, causing it to shut down for safety.

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

Parts commonly replaced

  • Return thermistor (NTC sensor)
  • Wiring harness
  • Main PCB

Related codes

Full explanation for L5
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 Shared across the INDEPENDENT System range

Parts commonly replaced

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

Related codes

Full explanation for L6
L8

Your boiler's main control board has lost its memory or settings, meaning it doesn't know how to operate correctly.

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

Parts commonly replaced

  • PCB
  • Wiring harness

Related codes

Full explanation for L8
L9

Your boiler's main control board has lost its memory or settings and needs to be reconfigured by a professional.

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

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for L9
LC

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

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

Parts commonly replaced

  • Main PCB
  • Gas valve
  • Electrodes

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 Shared across the INDEPENDENT System range

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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