Ideal Logic+ Heat H Fault codes & diagnostics

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

Heat Natural Gas 2016-present
GC Numbers 41-750-8241-750-8341-750-8441-750-8541-750-86
Download the Ideal Logic+ Heat H manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
18 High 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
41-750-82 LOGIC+ HEAT H12 2016–present
41-750-83 LOGIC+ HEAT H15 2016–present
41-750-84 LOGIC+ HEAT H18 2016–present
41-750-85 LOGIC+ HEAT H24 2016–present
41-750-86 LOGIC+ HEAT H30 2016–present
Just want the most common Ideal Logic+ Heat H faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 19 documented codes

Tap any card for details

F2

Your boiler has started to light but the flame has gone out unexpectedly, causing the system to shut down for safety.

High DIY-safe £120-£350

What to check first

  1. Check that your gas stopcock is fully open and other gas appliances like a hob are working.
  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 of the boiler control panel.

Parts commonly replaced

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

Related codes

Full explanation for F2
F3

Your boiler has stopped working because the fan that safely removes exhaust gases isn't spinning or communicating correctly with the system.

High Engineer only £250-£450

Parts commonly replaced

  • Fan assembly
  • PCB (Main circuit board)
  • Wiring harness

Related codes

Full explanation for F3
F4

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

High Engineer only £90-160

Parts commonly replaced

  • Flow thermistor (NTC sensor)
  • Wiring harness connectors

Related codes

Full explanation for F4
F5

Your boiler has detected a problem with the sensor that monitors the temperature of the water returning to it, which may cause the system to stop working correctly.

High Engineer only £90-180

Parts commonly replaced

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

Related codes

Full explanation for F5
F6

Your boiler has lost connection with its outdoor thermometer, which helps it adjust the heating based on the weather outside.

Low Engineer only £90-160

Parts commonly replaced

  • Outdoor weather compensation sensor
  • Sensor wiring

Related codes

Full explanation for F6
F7

Your boiler has detected that the electrical power coming from your mains supply is too low for it to operate safely.

High DIY-safe £100-350

What to check first

  1. Check if other appliances in your home are struggling or if lights are flickering
  2. Turn the boiler off and back on again to see if the voltage has stabilised
  3. Contact your electricity network provider to see if there is a known power issue in your local area

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Voltage Stabiliser

Related codes

Full explanation for F7
F8

Your boiler has detected an internal communication error or a electrical fault in its main control system, meaning it has safely shut down to prevent damage.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Gas Valve
  • Wiring Harness

Related codes

Full explanation for F8
F9

Your boiler's internal computer brain hasn't been set up correctly or there is an electrical issue with the part that controls the gas flow.

High Engineer only £180-450

Parts commonly replaced

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

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

  • Temperature thermistors
  • Flow and return sensors
  • Pump (if installed incorrectly)

Related codes

Full explanation for FA
FU

Your boiler has sensed that the water is heating up too quickly or isn't moving through the system properly, causing a large temperature difference that has forced the unit to shut down for safety.

High DIY-safe £120-350

What to check first

  1. Ensure all radiator valves (TRVs) are turned to their highest setting to allow water to flow.
  2. Check that any external zone valves are opening correctly.
  3. Verify that the system pump is running and hasn't become stuck.
  4. Bleed all radiators to remove trapped air that could be blocking circulation.

Parts commonly replaced

  • Central heating pump
  • Flow and return thermistors
  • Heat exchanger (if blocked by sludge)

Related codes

Full explanation for FU
L1

Your boiler has become too hot or water is not moving through the system properly, causing it to shut down for safety.

High DIY-safe £100-350

What to check first

  1. Check that your radiator valves are open and not turned to zero.
  2. Ensure your external heating pump is running if you have one.
  3. Reset the boiler by turning the control knob to the 'RESET' position and then back to 'ON'.

Parts commonly replaced

  • Circulation Pump
  • Thermistor (NTC Sensor)
  • Main Heat Exchanger

Related codes

Full explanation for L1
L2

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

High DIY-safe £100-£350

What to check first

  1. Check that your gas prepayment meter has credit (if applicable).
  2. Ensure your gas stopcock is fully open and other gas appliances like your hob are working.
  3. If it is freezing outside, check that your condensate pipe (the plastic pipe leading outside) isn't frozen and thaw it with warm water.
  4. Push the reset button on the front of the boiler once to restart the ignition sequence.

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Electrode
  • Gas Valve
  • Spark Leads

Related codes

Full explanation for L2
L4

Your boiler has stopped working because it cannot accurately measure the temperature of the water leaving the unit.

High Engineer only £90-160

Parts commonly replaced

  • Flow thermistor (NTC sensor)
  • Wiring harness

Related codes

Full explanation for L4
L5

Your boiler has stopped working because it cannot correctly measure the temperature of the water returning to the unit.

High Engineer only £90-160

Parts commonly replaced

  • Return Thermistor (NTC Sensor)
  • Wiring Harness

Related codes

Full explanation for L5
L6

Your boiler thinks it sees a flame even though it hasn't finished its startup sequence yet, so it has locked itself for safety.

High Engineer only £120-300

Parts commonly replaced

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

Related codes

Full explanation for L6
L7

Your boiler is failing to heat the water inside it properly, so it has shut itself down to protect its internal parts from damage.

High Engineer only £150-300

Parts commonly replaced

  • Circulation pump
  • Diverter valve
  • Heat exchanger
  • System filter

Related codes

Full explanation for L7
L8

Your boiler's electronic control system has lost its settings or is failing to communicate properly, which means the boiler cannot safely start up.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Gas Valve
  • Wiring Harness

Related codes

Full explanation for L8
L9

Your boiler has shut down because its internal computer and gas supply system are not communicating correctly or haven't been set up.

High Engineer only £180-450

Parts commonly replaced

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

Related codes

Full explanation for L9
LC

Your boiler has locked itself out because it has been reset too many times in a short period to protect its internal components.

High DIY-safe £0-120

What to check first

  1. Turn the boiler power off at the fused spur switch (the wall switch).
  2. Wait for at least 30 seconds.
  3. Turn the power back on to clear the lockout memory.

Parts commonly replaced

  • No parts usually required
  • Ignition Electrode
  • PCB

Related codes

Full explanation for LC
Status & diagnostic codes

1 operating states & engineer diagnostics

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

00 Status Your boiler is working perfectly and is currently in standby mode because it has reached the temperature set on your thermostat or programmer.
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