Ideal Logic Max System 2 Fault codes & diagnostics

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

System Natural Gas 2022-present
GC Numbers 41-796-9741-796-9841-796-9941-860-01
Download the Ideal Logic Max System 2 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.
1 Emergency 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
41-796-97 LOGIC MAX SYSTEM2 S15 2022–present
41-796-98 LOGIC MAX SYSTEM2 S18 2022–present
41-796-99 LOGIC MAX SYSTEM2 S24 2022–present
41-860-01 LOGIC MAX SYSTEM2 S30 2022–present
Just want the most common Ideal Logic Max System 2 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 20 documented codes

Tap any card for details

Blocked Flue/Condensate

Your boiler has shut down because smoke cannot exit the flue pipe or waste water cannot drain away through the condensate pipe.

High DIY-safe £80-220

What to check first

  1. Check if the white plastic pipe exiting your wall into an outside drain is frozen or blocked by debris.
  2. If frozen, gently pour warm (not boiling) water over the outdoor section of the pipe to melt the ice.
  3. Check the external flue terminal on your wall to ensure it isn't obstructed by leaves, bird nests, or snow.
  4. Hold the 'Reset' button for 3 seconds once any visible blockages are cleared.

Parts commonly replaced

  • Condensate trap
  • Pressure switch
  • Fan assembly
  • Flue seals

Related codes

Full explanation for Blocked Flue/Condensate
Fan Fault

Your boiler has detected an issue with its internal fan, which means it cannot safely blow away waste gases and has shut down to protect you.

High Engineer only £250-£450

Parts commonly replaced

  • Fan Assembly
  • Main PCB
  • Wiring Harness

Related codes

Full explanation for Fan Fault
Flame Loss

Your boiler started to heat up but the flame went out unexpectedly, causing the system to stop working for safety.

High DIY-safe £120-350

What to check first

  1. Check that your gas emergency control valve is open and other gas appliances are working.
  2. If you have a prepaid gas meter, ensure you have sufficient credit available.
  3. Restart the boiler by pressing the 'Reset' button on the front display.

Parts commonly replaced

  • Flame Sensing Electrode
  • Gas Valve
  • Spark Generator

Related codes

Full explanation for Flame Loss
Flame On Before Gas On

Your boiler thinks it sees a flame before any gas has even been released, which usually means a sensor is confused or there is a small internal leak.

Emergency Engineer only £120-350

Parts commonly replaced

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

Related codes

Full explanation for Flame On Before Gas On
Flow Thermistor Fault

Your boiler has stopped working because the internal sensor that monitors the temperature of the water leaving the unit has failed or is disconnected.

High Engineer only £120-£190

Parts commonly replaced

  • Flow Thermistor
  • Wiring Harness

Related codes

Full explanation for Flow Thermistor Fault
Gas Valve Fault

Your boiler has detected an issue with the valve that regulates the fuel supply, meaning it has safely shut itself down to prevent any risk.

High Engineer only £180-350

Parts commonly replaced

  • Gas Valve
  • Wiring Harness

Related codes

Full explanation for Gas Valve Fault
Ignition Lockout

Your boiler has failed to light, which means it cannot provide any heating or hot water until the gas supply or ignition system is restored.

High DIY-safe £90-280

What to check first

  1. Check if other gas appliances, such as a hob, are working to confirm gas is reaching the property
  2. Ensure your gas meter has credit and the emergency control valve is in the 'on' position
  3. Press the 'Restart' button on the front of the display panel

Parts commonly replaced

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

Related codes

Full explanation for Ignition Lockout
Low Mains Voltage

Your boiler has stopped working because the electricity supply coming into your home is not at a high enough voltage to power the internal components safely.

High Engineer only £100-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Voltage Stabiliser

Related codes

Full explanation for Low Mains Voltage
Low Water Pressure

Your boiler has stopped working because the water level inside the heating system has dropped too low and needs to be topped up.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop, which is usually a flexible silver hose with two small valves underneath the boiler.
  2. Slowly open both valve handles until you hear water running and watch the pressure gauge.
  3. Close both valves tightly once the pressure gauge reaches 1.5 bar.

Parts commonly replaced

  • External filling loop
  • Auto air vent
  • Expansion vessel

Related codes

Full explanation for Low Water Pressure
No Water Flow

Your boiler has stopped working because it cannot detect any water moving through the system to keep it running safely.

High DIY-safe £120-£350

What to check first

  1. Check that your boiler pressure gauge is between 1 and 1.5 bar
  2. If the pressure is too low, use the filling loop handles underneath the boiler to top it up
  3. Ensure all radiator valves and any isolation valves under the boiler are fully open

Parts commonly replaced

  • Circulation Pump
  • Water Pressure Sensor
  • Flow Turbine

Related codes

Full explanation for No Water Flow
Showing 11–20 of 20
Outside Sensor Fault

Your boiler has lost communication with the sensor that monitors the temperature outside, which may cause your heating to be less efficient or run at the wrong temperature.

Low Engineer only £90-180

Parts commonly replaced

  • Outside weather compensation sensor
  • External sensor wiring

Related codes

Full explanation for Outside Sensor Fault
Overheat Lockout

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

High DIY-safe £120-£450

What to check first

  1. Check that your central heating valves and radiator valves are fully open
  2. Ensure your system pressure is between 1.0 and 1.5 bar on the pressure gauge
  3. Press the 'Reset' button on the front of the boiler control panel

Parts commonly replaced

  • External Circulating Pump
  • Flow Thermistor
  • Overheat Thermostat
  • Diverter Valve

Related codes

Full explanation for Overheat Lockout
PCB Fault

The main computer board inside your boiler has malfunctioned, meaning the system can no longer control itself safely and has shut down.

High Engineer only £280-£450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring harness

Related codes

Full explanation for PCB Fault
Pump Dry Run

Your boiler has sensed that there isn't enough water circulating inside the system to operate safely, which stops it from over-heating.

High DIY-safe £0-180

What to check first

  1. Check the pressure gauge on the front of the boiler or under the casing.
  2. If the pressure is below 1.0 bar, use the filling loop handles to top the system up to 1.5 bar.
  3. Ensure all radiator valves are open and not stuck shut.
  4. Restart the boiler by pressing the 'Reset' button.

Parts commonly replaced

  • External Filling Loop
  • System Pump
  • Low Water Pressure Switch

Related codes

Full explanation for Pump Dry Run
Pump Fault

Your boiler has stopped circulating water around your heating system, meaning your radiators will not get warm.

High Engineer only £220-450

Parts commonly replaced

  • Central heating pump
  • Internal pump head
  • Main PCB

Related codes

Full explanation for Pump Fault
Pump Rotor Blocked

The main pump that moves hot water around your radiators and pipes has become stuck or seized.

High Engineer only £180-350

Parts commonly replaced

  • Circulating Pump
  • Pump Head
  • Magnetic Filter (Clean)

Related codes

Full explanation for Pump Rotor Blocked
Return Thermistor Fault

Your boiler has stopped working because it can no longer accurately monitor the temperature of the water returning from your radiators.

High Engineer only £120-£200

Parts commonly replaced

  • Return Thermistor (NTC Sensor)
  • Thermistor Wiring Harness

Related codes

Full explanation for Return Thermistor Fault
Room Thermostat Fault

Your heating controls cannot communicate with the boiler, which usually means the batteries in your wall thermostat have run out of power.

High DIY-safe £5-120

What to check first

  1. Locate your wall-mounted room thermostat or handheld controller.
  2. Remove the battery compartment cover or detach the unit from its backplate.
  3. Replace the old batteries with a fresh set of high-quality alkaline batteries (typically AA or AAA).
  4. Check the boiler display to see if the fault code has cleared and test the heating.

Parts commonly replaced

  • Batteries
  • Wireless Room Thermostat
  • Receiver Unit

Related codes

Full explanation for Room Thermostat Fault
Spare PCB Not Set

Your boiler's internal electronic control board has been replaced or reset but hasn't been programmed with the correct identity for this specific model.

High Engineer only £90-160

Parts commonly replaced

  • Main PCB

Related codes

Full explanation for Spare PCB Not Set
Too Many Restarts

Your boiler is repeatedly trying and failing to stay alight, so it has locked itself out to prevent further damage.

High Engineer only £100-280

Parts commonly replaced

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

Related codes

Full explanation for Too Many Restarts
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