Ideal Logic Max & Logic Plus Fault codes & diagnostics

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

Regular Natural GasLPG 12-30 kW 2018-present
GC Numbers 41-750-7041-750-7141-750-7241-750-7341-750-7441-750-8441-750-8541-750-8641-750-8741-750-88

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Severity at a glance

Each cell = one fault code. Hover to identify.
18 High 1 Low
Just want the most common Ideal Logic Max & Logic Plus faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 19 documented codes

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F2, FN or LN

Your boiler has lit correctly but the flame has gone out unexpectedly, meaning the system has shut down for safety.

High DIY-safe £100-350

What to check first

  1. Check if other gas appliances, like a cooker, are working to ensure gas is reaching the property
  2. Check if your gas meter has credit (if using a prepay meter)
  3. Press the Reset button on the front of the boiler

Parts commonly replaced

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

Related codes

Full explanation for F2, 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
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

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

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

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

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Voltage Regulator

Related codes

Full explanation for F7
F8

Your boiler's internal computer has lost its settings or suffered a technical failure and can no longer control the heating system.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for F8
F9

Your boiler's internal computer has lost its settings or suffered a technical failure and can no longer control the heating system.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for F9
FA

Your boiler has detected that the water is flowing in the wrong direction through the pipes or that the temperature sensors have been installed on the wrong pipes.

High Engineer only £100-250

Parts commonly replaced

  • Flow thermistor
  • Return thermistor
  • Pump

Related codes

Full explanation for FA
FD

Your boiler has stopped heating because water is not moving through the system properly.

High DIY-safe £100-£350

What to check first

  1. Check that your home's water pressure gauge is between 1 and 1.5 bar
  2. Open all radiator valves and ensure no radiators are blocked by air
  3. Restart the boiler by pressing the 'Reset' button

Parts commonly replaced

  • Circulation pump
  • Flow thermistor
  • Main PCB

Related codes

Full explanation for FD
FU

Your boiler has detected that water is heating up too quickly or not circulating properly, which usually means something is blocking the flow of water through the system.

High DIY-safe £90-250

What to check first

  1. Check that all blue-handled isolation valves underneath the boiler are fully turned to the open position
  2. Ensure all radiator valves (TRVs) are turned up to a high setting
  3. Check your central heating filter for any obvious blockages if you have one installed

Parts commonly replaced

  • Circulation pump
  • Main heat exchanger
  • Flow/Return thermistors

Related codes

Full explanation for FU
L1

Your boiler has shut down because it thinks the water inside is getting too hot or is not moving through the system properly.

High DIY-safe £100-350

What to check first

  1. Check that your radiator valves and any isolation valves are fully open
  2. Ensure your system pressure is topped up to between 1 and 1.5 bar
  3. Bleed your radiators to remove any trapped air and then reset the boiler

Parts commonly replaced

  • Circulating Pump
  • Thermistor (NTC Sensor)
  • Main Heat Exchanger (if blocked)

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

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

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

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

Parts commonly replaced

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

Related codes

Full explanation for L6
L8

Your boiler's internal computer has lost its settings or suffered a technical failure and can no longer control the heating system.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for L8
L9

Your boiler's internal computer has lost its settings or suffered a technical failure and can no longer control the heating system.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for L9
LC

Your boiler has tried to start five times in a row but failed to keep the flame alight, causing it to shut down as a safety precaution.

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 reaching the property
  2. Check if your gas meter has credit
  3. Press the 'Reset' button and wait for the boiler to restart

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Probe

Related codes

Full explanation for LC