Ideal Logic Combi C24 C30 C35 Fault codes & diagnostics

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

Combi Natural Gas 24-35 kW 2013-present
GC Numbers 47-348-5647-348-5747-348-58

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Each cell = one fault code. Hover to identify.
30 High 1 Medium 9 Low

All 40 documented codes

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C0

Your boiler's main control chip has lost communication with the circuit board, essentially meaning the brain and body are no longer speaking to each other.

High Engineer only £100-£350

Parts commonly replaced

  • Boiler Chip Card (BCC)
  • Printed Circuit Board (PCB)

Related codes

C2

Your boiler has lost communication with its internal computer chip, meaning the main control board no longer recognizes the specific model it is supposed to be operating.

High Engineer only £100-£350

Parts commonly replaced

  • Boiler Chip Card (BCC)
  • Printed Circuit Board (PCB)

Related codes

dU

Your boiler is not broken; it is simply in a special service mode used by engineers when they are preparing to replace internal parts.

Low DIY-safe

What to check first

  1. Turn the mains power to the boiler off
  2. Wait 30 seconds
  3. Turn the power back on to reset the boiler to normal operation
F1

Your boiler has detected that the water pressure inside the system is too low to run safely and has stopped working as a result.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose with one or two blue handles underneath the boiler).
  2. Slowly open the valve or valves until you hear water flowing and watch the pressure gauge.
  3. Close the valves tightly once the pressure gauge reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop tap
  • Expansion vessel re-pressurisation
  • Pressure sensor

Related codes

F2

Your boiler is failing to stay lit or cannot detect its own flame, meaning it has shut down for safety and will not provide heating or hot water.

High DIY-safe £100-280

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure gas supply is active
  2. If it is freezing outside, check if the white plastic condensate pipe leading outdoors is frozen and thaw it with warm water
  3. Press the 'Restart' button on the front control panel to reset the boiler

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead
  • Printed Circuit Board (PCB)

Related codes

F2 or Fn or Ln

Your boiler has started an ignition process but the flame has gone out, meaning the system has shut down for safety.

High DIY-safe £100-£350

What to check first

  1. Check that your gas stop tap is fully open and that you have credit on your gas meter.
  2. Check if other gas appliances in your home, such as a hob, are working correctly.
  3. Reset the boiler by turning the primary knob to the 'RESET' position and holding for five seconds.

Parts commonly replaced

  • Flame Sensing Electrode
  • Spark Generator
  • Gas Control Valve
  • Gas Meter Regulator

Related codes

F3

Your boiler has detected an issue with the internal fan, which is preventing the system from safely clearing exhaust gases and starting the ignition process.

High Engineer only £240-£450

Parts commonly replaced

  • Fan Assembly
  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

F4

Your boiler has detected an issue with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot safely regulate heat.

High Engineer only £90-£160

Parts commonly replaced

  • Flow Thermistor (NTC Sensor)
  • Wiring Harness

Related codes

F4 Or L4

Your boiler has stopped working because it is having trouble reading the temperature of the water flowing through it, so it has safely shut down to prevent overheating.

High Engineer only £120-220

Parts commonly replaced

  • Flow Thermistor (NTC Sensor)
  • Wiring harness

Related codes

F5

Your boiler has detected an issue with the sensor that monitors the temperature of the water returning to the unit, causing it to stop working for safety.

High Engineer only £90-160

Parts commonly replaced

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

Related codes

Showing 11–20 of 40
F5 Or L5

Your boiler has lost the ability to accurately measure 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 NTC Thermistor
  • Wiring harness

Related codes

F6

Your boiler has lost connection with the sensor that monitors the outdoor temperature, making it difficult for the system to adjust its heat settings efficiently.

Low Engineer only £90-180

Parts commonly replaced

  • Weather compensation sensor
  • Wiring harness

Related codes

F7

Your boiler has detected that the electricity supply coming into your home is at a lower voltage than it needs to operate safely.

High Engineer only £0-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Electrical Supply

Related codes

F8

Your boiler's computer brain has lost its settings or is experiencing an electrical fault, preventing the system from starting up.

High Engineer only £250-£550

Parts commonly replaced

  • Main PCB
  • Gas Valve
  • Ignition Lead

Related codes

F9

Your boiler's computer memory is blank or incorrect, meaning it doesn't currently know how to operate itself.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Customer ID Chip

Related codes

F9 or L9 or F8 or L8

Your boiler's main internal computer is failing to communicate correctly with its internal control systems, preventing it from safely starting up.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring harness
  • Gas valve

Related codes

FA

Your boiler has detected that the water temperature sensors are giving conflicting readings, often caused by the flow and return pipes being switched or a sensor failing.

High Engineer only £90-180

Parts commonly replaced

  • Flow Thermistor
  • Return Thermistor
  • Main PCB

Related codes

FL

Your boiler is displaying an error code for a feature that isn't actually used on this model, which usually indicates a simple electronic glitch or a programming error.

Medium DIY-safe £0-120

What to check first

  1. Locate the reset button on the front control panel.
  2. Press and hold the reset button for 2 seconds.
  3. Wait for the boiler to restart and check if the code has cleared.

Parts commonly replaced

  • None (Software reset)
  • Main PCB

Related codes

Fn

Your boiler has lit correctly but the flame has gone out unexpectedly, often due to a temporary interruption in the gas supply or a blocked condensate pipe.

High DIY-safe £100-£250

What to check first

  1. Check that your gas meter has credit and the isolation valve is open.
  2. Inspect the white plastic pipe (condensate) leading outside for signs of freezing or blockages.
  3. Restart the boiler by pressing the 'Reset' button.

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead

Related codes

FU

Your boiler has detected that the water is heating up too quickly or isn't moving through the system properly, causing it to overheat and shut down for safety.

High DIY-safe £120-£350

What to check first

  1. Check that at least two or three radiator valves are fully open to allow water flow.
  2. Ensure the large blue and red isolation valves underneath the boiler are in the 'open' position.
  3. Try resetting the boiler by turning the control knob to 'Reset' and then back to the original setting.

Parts commonly replaced

  • Central heating pump
  • Main heat exchanger
  • Thermistor (NTC sensor)

Related codes

Showing 21–30 of 40
L1

Your boiler has shut down because the water inside it has become too hot, usually due to a lack of circulation or a blockage in the system.

High DIY-safe £100-350

What to check first

  1. Check that your radiator valves are fully open.
  2. Ensure the boiler pressure is between 1 and 1.5 bar on the gauge.
  3. Reset the boiler by turning the control knob to 'Reset' and then back to 'On'.

Parts commonly replaced

  • Pump
  • Flow Thermistor
  • Heat Exchanger

Related codes

L2

Your boiler has stopped working because it cannot light a flame, which is often caused by a lack of gas supply or a blocked pipe.

High DIY-safe £100-350

What to check first

  1. Check if your gas meter has credit and that the gas emergency control valve is open.
  2. If it is freezing outside, check if your white condensate pipe is frozen and thaw it with warm water.
  3. Press the 'Restart' button on the boiler display to try again.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • PCB
  • Spark Generator

Related codes

L4

Your boiler has detected a problem with the internal temperature sensor that monitors 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

L4 or F4

Your boiler has stopped working because it can no longer accurately read the temperature of the water inside the unit.

High Engineer only £120-220

Parts commonly replaced

  • Flow thermistor (NTC sensor)
  • Wiring harness

Related codes

L5

Your boiler has detected a problem with the sensor that monitors the temperature of the water coming back into the unit, causing it to shut down for safety.

High Engineer only £90-180

Parts commonly replaced

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

Related codes

L5 or F5

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

High Engineer only £120-200

Parts commonly replaced

  • Return Thermistor
  • Wiring harness

Related codes

L6

Your boiler thinks a flame is present even though it hasn't been safely ignited, causing the system to shut down for safety.

High Engineer only £120-£350

Parts commonly replaced

  • Flame Sensing Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

L8

Your boiler's computer brain has lost its settings or is experiencing an electrical fault, preventing the system from starting up.

High Engineer only £250-£550

Parts commonly replaced

  • Main PCB
  • Gas Valve
  • Ignition Lead

Related codes

L9

Your boiler's computer brain has lost its settings or is experiencing an electrical fault, preventing the system from starting up.

High Engineer only £250-£550

Parts commonly replaced

  • Main PCB
  • Gas Valve
  • Ignition Lead

Related codes

LC

Your boiler has tried and failed to start up five times in a short window and has now locked itself out for safety.

High Engineer only £120-350

Parts commonly replaced

  • Flame Sensing Electrode
  • Ignition Lead
  • Gas Valve
  • PCB

Related codes

Showing 31–40 of 40
Ln

Your boiler is struggling to keep its flame lit, which means it cannot heat your water or radiators reliably.

High DIY-safe £100-£350

What to check first

  1. Check that your gas emergency control valve is open and you have credit on your gas meter.
  2. Check if other gas appliances in your home, like a hob, are working correctly.
  3. Reset the boiler by turning the mode knob to 'RE' and then back to your desired setting.
  4. During freezing weather, check that the white plastic condensate pipe leading outside is not frozen.

Parts commonly replaced

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

Related codes

oF

Your boiler is in a standby or programming mode and thinks it has been told to stay switched off.

High DIY-safe £0-280

What to check first

  1. Check that the boiler mode dial is turned to 'on' or the 'Hot Water and Heating' position
  2. Press and hold the 'Reset' button for three seconds
  3. Turn the power to the boiler off at the fused spur switch, wait 30 seconds, and turn it back on

Parts commonly replaced

  • None (Software reset)
  • Main PCB

Related codes

P1

Your boiler is displaying a service setting notification rather than a breakdown, indicating the internal pump is being told to run at its maximum speed.

Low DIY-safe £0-80

What to check first

  1. Press the 'Mode' or 'Reset' button to exit the installer function menu
  2. Switch the boiler off and back on at the main fused spur switch
  3. Monitor the display to see if the code clears and returns to the temperature display
P7

Your boiler is displaying a configuration setting rather than a breakdown, indicating the internal pump is set to its standard minimum operating speed.

Low DIY-safe

What to check first

  1. Press the 'Mode' or 'Reset' button to return the screen to the standard temperature display
  2. Observe if the code disappears and the boiler operates normally
  3. No further action is required if heating and hot water are functioning

Related codes

SE

Your boiler is simply reminding you that its annual service is due soon; it is a notification rather than a breakdown.

Low Engineer only £80-£120
SH

Your boiler is not in a fault state; it is simply running in a manual test mode designed for service engineers to check its performance.

Low DIY-safe

What to check first

  1. Press and hold the 'Preheat' and 'i' buttons together for 5 seconds.
  2. Restart the boiler using the power dial or reset button to exit the test mode.
  3. The display should return to the standard temperature or 'D' / 'C' status.

Related codes

SL

Your boiler is currently running a service test at its lowest power setting and this is a status indicator rather than a functional error.

Low DIY-safe

What to check first

  1. Wait for the service or commissioning process to finish
  2. Turn the selector knob to the 'Reset' position and then back to 'On'
  3. Restart the boiler by switching the power off and on at the fused spur

Related codes

UF

Your boiler is currently set to a professional test mode for servicing and is not in its normal operating state.

Low DIY-safe

What to check first

  1. Locate the 'Mode' or 'Reset' knob/button on the front panel.
  2. Turn the selector knob away from the 'Service' or 'Spanner' icon back to 'Auto' or 'On'.
  3. Press the 'Reset' button once if the code persists after changing the mode.
uP

Your boiler is currently stuck in its startup or programming sequence and is not yet ready to provide heat or hot water.

High DIY-safe £180-450

What to check first

  1. Wait up to 15 minutes for the programming cycle to finish automatically
  2. Turn the boiler power off at the fused spur switch, wait 30 seconds, and turn it back on
  3. Press and hold the 'Reset' button for 3 seconds

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Knob / Display Interface

Related codes

VF

Your boiler is performing a routine self-cleaning process to remove air bubbles from the system and is not actually reporting a hardware fault.

Low DIY-safe

What to check first

  1. Wait 5 minutes for the automatic venting cycle to complete
  2. Ensure your radiator valves are open to help air move through the system
  3. Check if the boiler display changes to '0' or a temperature once the 5 minutes have passed

Related codes