Ideal Instinct2 24 Fault codes & diagnostics

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

Combi Natural Gas 24 kW 2015 onwards Discontinued
GC Number 47-349-09
Download the Ideal Instinct2 24 manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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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.
43 High 2 Medium 1 Low
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
47-349-09 INSTINCT 24 2015–present
Just want the most common Ideal Instinct2 24 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 46 documented codes

Tap any card for details

F 1

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

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose with small taps) underneath the boiler.
  2. Slowly open both taps one at a time until you hear water entering the system.
  3. Watch the pressure gauge and close both taps tightly once the needle reaches 1.5 bar.
  4. Press the 'Restart' button on the boiler control panel to clear the fault code.

Parts commonly replaced

  • Filling loop valve
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for F 1
F 2

Your boiler has lost its gas supply or cannot detect a flame, meaning it cannot stay alight to provide heating or hot water.

High DIY-safe £80-250

What to check first

  1. Check if other gas appliances in your home, like a hob, are working correctly.
  2. Verify that your gas emergency control valve is in the 'on' position.
  3. Check your gas meter to ensure you have credit if you use a top-up or pre-payment system.
  4. Reset the boiler by pressing the reset button to see if it clears a temporary glitch.

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead

Related codes

Full explanation for F 2
F 3

Your boiler has stopped working because the fan that clears away waste gases is not spinning correctly or communicating with the system.

High Engineer only £280-£450

Parts commonly replaced

  • Fan Assembly
  • Main PCB
  • Wiring Harness

Related codes

Full explanation for F 3
F 4 L 4

Your boiler has detected a problem with the internal sensor that monitors the temperature of the water as it leaves the unit, causing it to shut down as a precaution.

High Engineer only £90-160

Parts commonly replaced

  • Flow Thermistor (NTC Sensor)
  • Wiring harness
  • Main PCB

Related codes

Full explanation for F 4 L 4
F 5 L 5

Your boiler has detected a problem with the sensor that monitors the temperature of the water returning from your radiators, preventing it from heating your home correctly.

High Engineer only £90-180

Parts commonly replaced

  • Return Thermistor (NTC sensor)
  • Connecting wiring harness

Related codes

Full explanation for F 5 L 5
F 6

Your boiler is having trouble reading the temperature outside, which helps it decide how hard it needs to work to heat your home.

Medium Engineer only £90-180

Parts commonly replaced

  • Weather compensation sensor
  • Sensor wiring
  • PCB

Related codes

Full explanation for F 6
F 7

Your boiler has detected that the electricity supply from the mains is too low for it to operate safely and has shut down to protect its internal components.

High Engineer only £100-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Voltage Regulator/Transformer

Related codes

Full explanation for F 7
F 9 L 9

Your boiler's internal computer brain hasn't 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)
  • Code Chip

Related codes

Full explanation for F 9 L 9
F A

Your boiler has detected an unusual temperature difference between the water leaving and returning to the unit, suggesting a sensor or circulation internal error.

High Engineer only £120-£240

Parts commonly replaced

  • Flow Thermistor
  • Return Thermistor
  • Main PCB

Related codes

Full explanation for F A
F H

Your boiler has detected that water is not moving through the system properly, which has caused it to stop working to prevent overheating.

High DIY-safe £120-£350

What to check first

  1. Check the pressure gauge and top it up to 1.5 bar if it is low
  2. Ensure all radiator valves and isolation valves under the boiler are fully open
  3. Check for any visible leaks around the pipework or radiators
  4. Reset the boiler by turning the dial to 'reset' for a few seconds

Parts commonly replaced

  • Central heating pump
  • Flow thermistor
  • Flow switch

Related codes

Full explanation for F H
Showing 11–20 of 46
F L

Your boiler has detected that there is not enough water circulating through the system to operate safely, which is usually caused by low water pressure or an air lock.

High DIY-safe £0-220

What to check first

  1. Check the pressure gauge on the front of the boiler; if it is below 1 bar, use the filling loop to top it up to 1.5 bar.
  2. Ensure all radiator valves and boiler isolation valves are fully open.
  3. Restart the boiler by pressing the reset button once the pressure is corrected.

Parts commonly replaced

  • Circulation Pump
  • Water Pressure Sensor
  • Automatic Air Vent

Related codes

Full explanation for F L
F P

Your boiler's internal pump has stopped spinning, preventing heated water from moving around your radiators and taps.

High Engineer only £220-£450

Parts commonly replaced

  • Circulating Pump
  • Pump Head
  • Central Heating Filter

Related codes

Full explanation for F P
F U

Your boiler has detected that the water is not flowing through the pipes quickly enough, causing a large temperature gap between the outgoing and incoming pipes.

High DIY-safe £90-250

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar on the gauge
  3. Check for any visible leaks around the radiators or pipework
  4. Bleed all radiators to remove trapped air

Parts commonly replaced

  • Circulation Pump
  • System Filter (Cleaned)
  • Main Heat Exchanger (De-sludge)

Related codes

Full explanation for F U
F[-]

Your boiler has detected an internal fault that needs technical attention, but it has not specified exactly which component is failing yet.

High Engineer only £100-280

Parts commonly replaced

  • Main PCB
  • Internal Wiring Harness
  • Control Display

Related codes

Full explanation for F[-]
F1

Your boiler has detected that there is not enough water in the system to operate safely, causing it to shut down temporarily.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose with one or two small black taps) underneath the boiler.
  2. Slowly open the tap(s) until you hear water entering the system.
  3. Watch the pressure gauge and close the taps firmly once the needle reaches between 1 and 1.5 bar.
  4. Reset the boiler by pressing the 'Restart' button.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for F1
F2

Your boiler has started to ignite but the flame has gone out, meaning the system has shut down for safety and you will not have any heating or hot water.

High DIY-safe £120-£350

What to check first

  1. Check if other gas appliances in your home (like a hob) are working to ensure gas is being supplied
  2. Check that your gas pre-payment meter (if you have one) has sufficient credit
  3. Press the Reset button on the front of the boiler display panel

Parts commonly replaced

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

Related codes

Full explanation for F2
F2 or Fn or Ln

Your boiler has started an ignition sequence but the flame has either failed to light or gone out unexpectedly, meaning it cannot provide heat or hot water.

High DIY-safe £100-350

What to check first

  1. Check if other gas appliances in your home, like a gas hob, are working to ensure gas is reaching the property
  2. Ensure your gas pre-payment meter (if applicable) has credit
  3. Press and hold the 'RESTART' button for two seconds to see if the boiler resets successfully

Parts commonly replaced

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

Related codes

Full explanation for F2 or Fn or Ln
F3

Your boiler has detected an issue with the electrical fan which is preventing it from safely starting up to provide heating or hot water.

High Engineer only £220-£450

Parts commonly replaced

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

Related codes

Full explanation for F3
F4

Your boiler's internal thermometer that monitors the water temperature leaving the unit has stopped working correctly, causing the system to shut down for safety.

High Engineer only £90-160

Parts commonly replaced

  • Flow Thermistor (NTC Sensor)
  • Wiring Harness

Related codes

Full explanation for F4
F5

Your boiler has detected a problem with the sensor that monitors the temperature of the water coming back into the unit, causing it to stop working as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

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

Related codes

Full explanation for F5
Showing 21–30 of 46
F6

Your boiler is having trouble communicating with the heat sensor located on the outside of your house, which helps it decide how hard to work based on the weather.

Low DIY-safe £90-160

What to check first

  1. Turn the boiler power switch off and back on again to see if the error clears.
  2. Check if the sensor on your outside wall has been knocked or damaged by garden work.
  3. Ensure there is no heavy snow or debris covering the outside sensor box.

Parts commonly replaced

  • External weather compensation kit
  • Sensor wiring

Related codes

Full explanation for F6
F7

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

High DIY-safe £0-120

What to check first

  1. Check if there is a regional power cut or brownout in your local area
  2. Ensure your boiler is plugged directly into a wall socket and not into a low-quality extension lead
  3. Turn the boiler off and back on again once the local grid power has stabilised

Parts commonly replaced

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

Related codes

Full explanation for F7
F8

Your boiler's internal computer brain is confused or has lost its settings, causing it to stop working for safety reasons.

High DIY-safe £100-£350

What to check first

  1. Press the Reset button once and wait for the boiler to restart
  2. Switch off the power supply to the boiler at the fuse spur for 30 seconds, then switch it back on
  3. If the code persists after resetting twice, call a Gas Safe registered engineer

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring harness

Related codes

Full explanation for F8
F8 or L8

Your boiler's internal computer has lost its settings or there is an electrical fault, meaning the system has shut down for safety.

High Engineer only £250-£550

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Gas Valve Wiring Harness
  • Gas Valve

Related codes

Full explanation for F8 or L8
F9

Your boiler's internal computer has encountered a critical error and can no longer control the heating system safely.

High Engineer only £250-£450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for F9
F9 or L9

Your boiler's internal computer has suffered a critical error and can no longer control the heating or hot water safely.

High Engineer only £280-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for F9 or L9
FA

Your boiler has stopped working because it has detected an unusual temperature difference between the water leaving and returning to the unit, suggesting a sensor error or a flow issue.

High Engineer only £90-180

Parts commonly replaced

  • Flow thermistor
  • Return thermistor
  • Wiring harness

Related codes

Full explanation for FA
Fn

Your boiler is failing to stay lit, which means the system cannot get the heat it needs to provide you with hot water or warming for your radiators.

High DIY-safe £120-350

What to check first

  1. Check if other gas appliances, like a cooker, are working to ensure gas is reaching the property
  2. If it is freezing outside, check that the white plastic condensate pipe leading outdoors is not frozen
  3. Press and hold the 'Restart' button for two seconds to attempt a reset

Parts commonly replaced

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

Related codes

Full explanation for Fn
FP

Your boiler's water pump is struggling to circulate water because it is stuck or jammed, which means the system cannot heat your radiators or tap water.

High Engineer only £120-250

Parts commonly replaced

  • Central heating pump
  • Pump head

Related codes

Full explanation for FP
FU

Your boiler is overheating because the water isn't moving through the system quickly enough to be cooled down.

High DIY-safe £120-280

What to check first

  1. Check that the two blue or black isolation valves underneath the boiler are fully open.
  2. Ensure at least two or three radiators have their valves turned to the highest setting.
  3. Check if the boiler pressure gauge is between 1 and 1.5 bar; top up if it is too low.

Parts commonly replaced

  • Circulation Pump
  • Pump Head
  • Main Heat Exchanger (if blocked)

Related codes

Full explanation for FU
Showing 31–40 of 46
L 1

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

High DIY-safe £100-350

What to check first

  1. Check the pressure gauge on the front of the boiler is between 1 and 1.5 bar
  2. Open all radiator valves to ensure water can flow freely
  3. Switch the boiler off and back on at the mains to reset the system

Parts commonly replaced

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

Related codes

Full explanation for L 1
L 2

Your boiler is failing to light the gas to start the heating or hot water process, and has locked itself for safety after 5 attempts.

High DIY-safe £100-£350

What to check first

  1. Check that your gas prepayment meter has credit (if applicable)
  2. Check that other gas appliances, like a cooker hob, are working to confirm gas supply
  3. Press and hold the 'Restart' button for two seconds to see if the boiler resets
  4. In freezing weather, check that the white plastic condensate pipe outside is not frozen

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Spark generator
  • Ionisation probe

Related codes

Full explanation for L 2
L 6

Your boiler thinks a flame is present when there shouldn't be one, so it has locked itself for safety.

High Engineer only £120-280

Parts commonly replaced

  • Ionisation Probe
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for L 6
L C

Your boiler has stopped working because it has tried to reset itself five times in a short period due to a persistent underlying fault.

High Engineer only £100-350

Parts commonly replaced

  • Spark Electrode
  • Ionisation Probe
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for L C
L[-]

Your boiler has stopped working and locked itself for safety because it has detected a specific internal fault or failed to fire correctly multiple times.

High DIY-safe £90-£350

What to check first

  1. Check that your gas pre-payment meter (if applicable) has credit and the gas valve is open.
  2. Rotate the 'Mode' knob to the 'Reset' position and hold it for 2 seconds, then turn it back to your desired setting.
  3. Ensure your condensate pipe has not frozen if it is currently cold outside.

Parts commonly replaced

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

Related codes

Full explanation for L[-]
L1

Your boiler has sensed it is getting too hot and has shut itself down as a safety precaution.

High DIY-safe £100-350

What to check first

  1. Check that all radiator valves (TRVs) are fully open to allow water to flow.
  2. Ensure there is enough water pressure in the system by checking the gauge is between 1 and 1.5 bar.
  3. Reset the boiler by turning the control knob to the 'Reset' position and holding for 2 seconds.

Parts commonly replaced

  • Circulating Pump
  • Thermistor (NTC Sensor)
  • Main Heat Exchanger (Descaling)

Related codes

Full explanation for L1
L2

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

High DIY-safe £100-£350

What to check first

  1. Check if your gas supply is active (e.g., check if a gas hob lights or if your prepay meter has credit).
  2. Check if the condensate pipe (the plastic pipe running outside) is frozen or blocked.
  3. Reset the boiler by pressing the 'RE' button or turning the dial to reset for 2 seconds.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Spark Lead
  • Ionisation Probe

Related codes

Full explanation for L2
L4

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

High Engineer only £90-160

Parts commonly replaced

  • Flow Thermistor (NTC sensor)
  • Connecting wiring harness

Related codes

Full explanation for L4
L4 or F4

Your boiler has detected an issue with the sensor that monitors the temperature of the water leaving the unit, causing it to shut down for safety.

High Engineer only £90-160

Parts commonly replaced

  • Flow Thermistor (NTC Sensor)
  • Wiring Harness

Related codes

Full explanation for L4 or F4
L5

Your boiler has detected an issue with a temperature sensor that monitors 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 connecting the sensor

Related codes

Full explanation for L5
Showing 41–46 of 46
L5 or F5

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

High Engineer only £90-160

Parts commonly replaced

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

Related codes

Full explanation for L5 or F5
L6

Your boiler has sensed a flame inside the unit when there shouldn't be one, causing it to shut down for safety purposes.

High Engineer only £120-£350

Parts commonly replaced

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

Related codes

Full explanation for L6
L8

Your boiler's internal computer is having trouble reading its own settings and has shut down as a precaution.

High Engineer only £120-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • User Interface/Display Board

Related codes

Full explanation for L8
L9

Your boiler's main internal computer has developed a malfunction and is no longer able to control the system.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for L9
LC

Your boiler has been manually reset too many times in a short window and has temporarily locked itself to prevent further strain or damage.

Medium DIY-safe £0-120

What to check first

  1. Turn off the power supply to the boiler at the fused spur switch (the wall switch near the boiler).
  2. Wait for at least 5 minutes to allow the internal timer to clear.
  3. Turn the power back on and wait for the boiler to finish its startup sequence without pressing the reset button.

Parts commonly replaced

  • No parts usually required for LC code itself
  • Ignition Electrode (if original fault persists)
  • PCB (if software reflects permanent lock)

Related codes

Full explanation for LC
Ln

Your boiler is struggling to keep its flame lit, which means the system has safely shut down to prevent unburnt gas from building up.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances, like a cooker, are working to confirm your gas supply is active.
  2. If you have a prepaid gas meter, check that you have sufficient credit.
  3. Press the Reset button once to see if the boiler restarts normally.

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve
  • Condensate Trap

Related codes

Full explanation for Ln
Status & diagnostic codes

11 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

00 Status Your boiler is working perfectly fine and is simply waiting for you to turn up the thermostat or use the hot water. CH Status Your boiler is working normally and is currently providing heat to your radiators. CH 80 Status Your boiler has reached the required temperature and is temporarily pausing the burner while the pump continues to circulate heat around your radiators. FP 1 0 Status Your boiler has detected that the water temperature has dropped too low and is automatically running to prevent the pipes from freezing. H Status Your boiler is working normally and simply indicating that it is currently heating up water for your taps. H 60 Status Your boiler has reached its maximum temperature for hot water and is temporarily pausing to prevent overheating, which often occurs if the water flow is too slow or a sensor is drifting. oF Diagnostic Your boiler is currently stuck in a setup mode used for programming its internal computer chip and needs to be properly configured by a professional. PH Status Your boiler is notifying you that the function which keeps hot water ready for instant use is currently active. PH 60 Status Your boiler is currently heating up a small amount of water internally so that your hot water arrives at the taps more quickly. U Diagnostic Your boiler is currently set to a professional maintenance mode used for draining or servicing the internal system. uP Diagnostic Your boiler is waiting for its new control board to be configured to the correct model number after being switched on.