Ideal Compact Fault codes & diagnostics

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

Combi Natural Gas 24-28 kW 2006-2010 Discontinued

Replaced by: Logic Combi

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31 High 2 Low

All 33 documented codes

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C0

Your boiler has failed to recognize its internal memory chip, meaning it has forgotten its specific settings and cannot operate for your safety.

High Engineer only £120-£350

Parts commonly replaced

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

Related codes

C2

Your boiler's electronic memory card has developed a communication fault or is missing, preventing the system from operating.

High Engineer only £120-280

Parts commonly replaced

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

Related codes

F1

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

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath your boiler.
  2. Open the one or two taps on the hose until you hear water flowing and the pressure gauge reaches 1.5 bar.
  3. Close the taps tightly and press the restart button on the front of the boiler.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

F2

Your boiler has started to fire up 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 open and other gas appliances are working
  2. If you have a pre-payment meter, ensure you have credit available
  3. Reset the boiler by turning the mode dial to 'reset' and then back to your desired setting

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead

Related codes

F2, FN or LN

Your boiler is failing to stay lit or cannot detect its own flame, meaning it has stopped providing heating and hot water for safety.

High DIY-safe £100-350

What to check first

  1. Check if other gas appliances, like a hob, are working to confirm gas supply.
  2. If it is freezing outside, check if the white plastic condensate pipe is frozen and thaw it with warm water.
  3. Press the 'Reset' button on the front of the boiler once.

Parts commonly replaced

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

Related codes

F3

Your boiler has detected an issue with the electrical fan, meaning it cannot safely clear exhaust fumes and has stopped running for safety.

High Engineer only £250-£450

Parts commonly replaced

  • Fan assembly
  • Air Pressure Switch
  • Main PCB

Related codes

F4

Your boiler has lost its ability to accurately measure the temperature of the water leaving the unit, meaning it cannot operate safely and has shut down as a precaution.

High Engineer only £90-160

Parts commonly replaced

  • Flow thermistor (NTC sensor)
  • Connecting wiring harness

Related codes

F5

Your boiler has lost its ability to accurately measure the temperature of the water coming back from your radiators, which prevents it from running smoothly.

High Engineer only £100-£180

Parts commonly replaced

  • Return thermistor (NTC sensor)
  • Wiring harness

Related codes

F6

Your boiler's external temperature sensor has stopped communicating correctly, which means the system may struggle to adjust your heating efficiency based on the weather outside.

Low Engineer only £90-160

Parts commonly replaced

  • Outside weather compensation sensor
  • Sensor wiring harness

Related codes

F7

Your boiler has detected that the incoming electricity supply is not at the correct voltage, meaning it cannot operate safely or effectively.

High Engineer only £0-250

Parts commonly replaced

  • Main PCB
  • External Voltage Regulator

Related codes

Showing 11–20 of 33
F9

Your boiler’s internal computer has not been set up correctly to tell it which model it is, meaning it doesn't know how to operate safely.

High Engineer only £100-£350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Configuration Chip

Related codes

F9, L9, F8 or L8

Your boiler's internal computer has lost its settings or suffered an electrical failure, meaning it can no longer communicate with the rest of the unit.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • PCB Configuration Chip

Related codes

FA

Your boiler has detected that the water pipes connected to the unit are likely installed in the wrong positions, or a sensor is misreading the temperature direction.

High Engineer only £90-250

Parts commonly replaced

  • Flow thermistor
  • Return thermistor
  • Main PCB

Related codes

FD

Your boiler has stopped working because there is not enough water pressure or flow to safely circulate around the system.

High DIY-safe £100-280

What to check first

  1. Check the pressure gauge on the front of the boiler is between 1 and 1.5 bar
  2. If pressure is low, use the filling loop handles underneath to top up the water
  3. Ensure all radiator valves and boiler isolation valves are fully open

Parts commonly replaced

  • Circulating Pump
  • Water Pressure Sensor
  • Filling Loop

Related codes

Flow return reversed

Your boiler has detected that the temperature sensors on the main pipes are confused, likely because a internal sensor has come loose or failed.

High Engineer only £90-160

Parts commonly replaced

  • Flow Thermistor
  • Return Thermistor
  • Wiring Harness

Related codes

Flow/Return reversed

Your boiler has sensed that the water temperatures are the wrong way around, likely because a sensor has come loose or stopped working correctly.

High Engineer only £90-180

Parts commonly replaced

  • Flow Thermistor
  • Return Thermistor

Related codes

FU

Your boiler has detected that the water is heating up too quickly or not circulating properly, which usually means the water flow is blocked.

High DIY-safe £80-250

What to check first

  1. Check that the stop taps (isolation valves) underneath the boiler are in the open position.
  2. Ensure all radiator valves are turned on and not stuck closed.
  3. Reset the boiler by turning the mode dial to 'reset' for two seconds and then back to your desired setting.

Parts commonly replaced

  • Pump
  • Flow/Return Thermistor
  • Main Heat Exchanger (if blocked)

Related codes

Ignition lockout

Your boiler has tried to light several times but cannot establish a stable flame, meaning your heating and hot water will not work.

High DIY-safe £100-350

What to check first

  1. Check if other gas appliances, like a cooker or hob, are working to ensure gas is reaching your home.
  2. If you have a prepaid gas meter, ensure it has credit.
  3. Press the Reset button on the boiler display for 3 seconds to attempt a restart.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • PCB (Printed Circuit Board)

Related codes

L1

Your boiler has stopped working because it has detected it is getting too hot too quickly or there is not enough water moving through the system.

High DIY-safe £120-£350

What to check first

  1. Check that your system pressure is between 1 and 1.5 bar on the pressure gauge
  2. Ensure all radiator valves are fully open to allow water to flow
  3. Check for any visible leaks around the boiler and pipework
  4. Press the reset button to see if the fault clears

Parts commonly replaced

  • Circulating pump
  • Thermistor (NTC sensor)
  • Diverter valve

Related codes

L2

Your boiler has tried to light several times but cannot establish a flame, meaning it has shut down for safety.

High DIY-safe £100-£350

What to check first

  1. Check that your gas emergency control valve is open and other gas appliances like your hob are working.
  2. If you have a prepaid meter, ensure you have sufficient credit available.
  3. Press and hold the reset button for three seconds to attempt a restart.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensing probe
  • PCB

Related codes

Showing 21–30 of 33
L4 or F4

Your boiler has detected that water is either not moving through the system or a temperature sensor has failed, causing it to shut down to prevent overheating.

High Engineer only £90-180

Parts commonly replaced

  • Flow Thermistor
  • Return Thermistor
  • Thermistor Clip

Related codes

L5

Your boiler has been manually reset too many times in a short window and has now locked itself out for safety.

High DIY-safe £0-120

What to check first

  1. Turn the power to the boiler off at the fused spur switch
  2. Wait for at least 30 seconds
  3. Turn the power back on and wait for the boiler to reboot

Parts commonly replaced

  • No parts usually required
  • Printed Circuit Board (PCB)

Related codes

L5 or 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 running for safety.

High Engineer only £90-160

Parts commonly replaced

  • Return thermistor (NTC sensor)
  • Wiring harness / connector
  • Printed Circuit Board (PCB)

Related codes

L6

Your boiler thinks it sees a flame even though it hasn't started yet, which is causing it to shut down for safety.

High Engineer only £120-350

Parts commonly replaced

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

Related codes

LC

Your boiler has likely experienced a temporary communication error or a small software glitch during startup.

Low DIY-safe £0-120

What to check first

  1. Switch off the electrical power supply to the boiler at the fused spur switch.
  2. Wait for approximately 30 seconds.
  3. Switch the power back on and see if the boiler restarts normally.

Parts commonly replaced

  • None (usually resolved by reset)
  • Printed Circuit Board (PCB) if fault recurs

Related codes

Low mains voltage

Your boiler is not receiving enough electrical power to operate correctly, which is often caused by a general power issue or a faulty internal component.

High Engineer only £180-350

Parts commonly replaced

  • Water Pump
  • Printed Circuit Board (PCB)

Related codes

Low water pressure

Your boiler has detected that the water level inside the system is too low to operate safely, which is usually caused by a small leak or air being bled from radiators.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually two silver braided hoses under the boiler).
  2. Open the small taps on the filling loop until you hear water flowing.
  3. Watch the pressure gauge until it reaches 1.5 bar, then close the taps tightly.

Parts commonly replaced

  • Filling loop valves
  • Pressure sensor
  • Automatic air vent

Related codes

Overheat lockout

Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.

High DIY-safe £100-280

What to check first

  1. Check that all radiator valves and boiler service valves are fully open
  2. Bleed all radiators to remove trapped air from the system
  3. Repressurise the system to 1.0 bar using the filling loop
  4. Press the reset button on the boiler control panel

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger (if blocked)

Related codes

Pump rotor blocked

Your boiler's internal water circulator has stopped spinning, which prevents heat from moving through your home and can cause the system to shut down.

High Engineer only £180-£350

Parts commonly replaced

  • Central heating pump
  • Internal bypass valve

Related codes

Thermal fuse lockout

Your boiler has overheated and shut itself down as a safety precaution to prevent damage.

High DIY-safe £0-120

What to check first

  1. Check that all radiator valves are open and there is water in the system
  2. Locate the reset button on the boiler control panel
  3. Press the reset button and wait for the boiler to restart

Parts commonly replaced

  • Overheat Thermostat
  • Thermal Fuse
  • Main Heat Exchanger

Related codes

Showing 31–33 of 33
Too many resets

Your boiler has been manually reset too many times in a short window and has temporarily locked itself to prevent potential damage or mask an underlying fault.

High DIY-safe £80-£350

What to check first

  1. Turn the power to the boiler off at the fused spur switch
  2. Wait for at least 15 to 30 minutes without touching any buttons
  3. Turn the power back on and check if the lockout has cleared

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Control Valve
  • PCB

Related codes

Too many restarts

Your boiler is trying to fire up too many times in a short window because it is struggling to stay lit, causing it to lock itself out for safety.

High DIY-safe £100-280

What to check first

  1. Locate the boiler's power switch (usually a fused spur on the wall near the unit).
  2. Turn the power off, wait for 30 seconds, and turn it back on to reset the electronics.
  3. Check that your gas supply is active and that any external valves are open.

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve

Related codes

Water pressure

Your boiler has lost the water pressure it needs to push heat around your home, likely due to a small leak or air in the system.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (the flexible silver hose) underneath or near the boiler
  2. Slowly open the valve(s) until you hear water flowing and the pressure gauge reaches 1.0 to 1.5 bar
  3. Close the valve(s) tightly and reset the boiler if required

Parts commonly replaced

  • Filling loop
  • Expansion vessel re-pressurisation
  • Automatic air vent

Related codes