Baxi 100/2 HE Plus Fault codes & diagnostics

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

Regular Gas 2004-2006 Discontinued
GC Number 41-075-34
Download the Baxi 100/2 HE Plus manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
16 High 1 Medium 3 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
41-075-34 100/2 HE Plus 2004–2006
Just want the most common Baxi 100/2 HE Plus 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

LED / flash-pattern codes
1 red flash

Your boiler has sensed that it is getting too hot or that water isn't moving through the system properly, causing it to shut down for safety.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure your system water pressure is between 1 and 1.5 bar
  3. Press the reset button firmly for 5 seconds

Parts commonly replaced

  • Temperature thermistor (NTC sensor)
  • Circulating pump
  • Overheat thermostat

Related codes

Full explanation for 1 red flash
2 red flashes

Your boiler has become too hot and has automatically shut down for safety.

High DIY-safe £100-350

What to check first

  1. Wait for the boiler to cool down for at least 20 minutes
  2. Press the 'Reset' button on the control panel
  3. Check that your radiator valves are open and that your pump is running

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • PCB (Printed Circuit Board)

Related codes

Full explanation for 2 red flashes
3 green flashes

Your boiler is temporarily losing its flame and is currently trying to fix the problem by restarting itself.

Medium Engineer only £120-350

Parts commonly replaced

  • Flame rectification probe
  • Ignition lead
  • PCB (Control board)
  • Gas valve

Related codes

Full explanation for 3 green flashes
3 red flashes

Your boiler is failing to light the burner after several attempts, which means your heating and hot water will not work.

High DIY-safe £120-350

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. If you have a pre-payment meter, ensure you have credit and the meter is active
  3. Press the reset button once to see if the boiler initiates a successful ignition cycle

Parts commonly replaced

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

Related codes

Full explanation for 3 red flashes
4 green flashes

Your boiler's internal computer parts are temporarily struggling to talk to each other, but the system should usually fix itself automatically.

Low DIY-safe £180-350

What to check first

  1. Wait up to 15 minutes for the boiler to self-reset
  2. Press the reset button briefly if the light continues to flash
  3. Turn the boiler power off and back on at the fused spur switch

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 4 green flashes
4 red flashes

Your boiler has stopped working because the internal component responsible for clearing waste gases safely out of the flue is not spinning correctly or has failed.

High Engineer only £250-450

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 4 red flashes
5 green flashes

Your boiler has experienced a temporary computer glitch that it is currently trying to fix itself.

Low DIY-safe £0-120

What to check first

  1. Wait for the boiler to automatically reset itself
  2. If the flashing continues for more than 10 minutes, turn the control knob to 'Reset' and then back to the desired temperature
  3. Monitor the boiler to see if the green light returns to a steady state

Parts commonly replaced

  • No parts usually required
  • Printed Circuit Board (PCB) if fault persists
Full explanation for 5 green flashes
5 red flashes

Your boiler's internal memory chip has developed a communication fault, meaning it can no longer remember how to operate correctly.

High Engineer only £180-350

Parts commonly replaced

  • Parameter storage unit (PSU)
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 5 red flashes
6 green flashes

Your boiler has experienced a brief internal glitch and is currently trying to restart itself automatically.

Low DIY-safe £0-120

What to check first

  1. Wait for the boiler to complete its self-reset process
  2. If the flashing continues for more than 15 minutes, press the 'Reset' button once
  3. Ensure your electricity supply is stable and not fluctuating

Parts commonly replaced

  • Control PCB
  • Ignition Electrode

Related codes

Full explanation for 6 green flashes
6 red flashes

Your boiler has encountered an internal technical error and has safely shut itself down to prevent damage.

High Engineer only £180-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Ignition Lead
  • Main Cable Harness
Full explanation for 6 red flashes
Showing 11–20 of 20
FLASH OFF ON

Your boiler has become too hot and has automatically shut down to protect itself.

High DIY-safe £120-350

What to check first

  1. Locate the reset button on the front control panel.
  2. Press and hold the reset button for at least 5 seconds.
  3. Ensure your radiator valves are open and your system pressure is adequate if a gauge is visible.

Parts commonly replaced

  • Circulating Pump
  • Overheat Thermostat
  • Main PCB
  • Thermistor
Full explanation for FLASH OFF ON
FLASH ON FLASH

Your boiler's internal computer has developed a fault and can no longer control the heating process safely.

High Engineer only £240-£450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • PCB Ignition Lead
Full explanation for FLASH ON FLASH
FLASH ON ON

Your boiler's internal computer has failed and can no longer control the heating process safely.

High Engineer only £280-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • PCB Ignition Lead

Related codes

Full explanation for FLASH ON ON
ON FLASH FLASH

Your boiler has detected that water isn't moving through the system properly or there isn't enough water inside, causing it to overheat quickly.

High DIY-safe £120-£350

What to check first

  1. Check if your system pressure gauge is too low and top it up if needed
  2. Ensure all radiator valves and boiler isolation valves are fully open
  3. Gently bleed your radiators to remove any trapped air pockets

Parts commonly replaced

  • Circulating Pump
  • Overheat Thermostat
  • Printed Circuit Board (PCB)

Related codes

Full explanation for ON FLASH FLASH
ON FLASH ON

Your boiler has stopped working because its internal temperature sensor is reporting an error and needs attention.

High Engineer only £90-160

Parts commonly replaced

  • Thermistor (NTC Sensor)
  • Wiring harness

Related codes

Full explanation for ON FLASH ON
ON ON FLASH

Your boiler's internal computer brain has developed a critical fault and is unable to control the heating process safely.

High Engineer only £280-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring Harness

Related codes

Full explanation for ON ON FLASH
Digital codes
110

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

High DIY-safe £100-280

What to check first

  1. Check that all radiator valves are fully open
  2. Bleed your radiators to remove trapped air using a radiator key
  3. Wait for the boiler to cool down and press the reset button

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • NTC Temperature Sensor

Related codes

Full explanation for 110
125

Your boiler has likely overheated because water isn't moving through the system properly, causing the unit to shut down for safety.

High DIY-safe £120-£350

What to check first

  1. Check that your radiator valves and isolation valves are fully open
  2. Bleed your radiators to remove trapped air from the system
  3. Gently press the reset button on the front of the boiler panel

Parts commonly replaced

  • Central heating pump
  • Overheat thermostat
  • Flow temperature sensor

Related codes

Full explanation for 125
160

Your boiler has stopped working because the internal fan, which safely exhausts gases, is not spinning at the correct speed or has failed completely.

High Engineer only £220-£380

Parts commonly replaced

  • Fan Assembly
  • PCB (Printed Circuit Board)
  • Air Pressure Switch

Related codes

Full explanation for 160
Status & diagnostic codes

2 operating states & engineer diagnostics

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

1 green flash Status Your boiler has reached the correct temperature and is simply taking a normal break until more heat is needed. CN12 Diagnostic Your boiler has lost its specific configuration settings, meaning it has forgotten how to correctly control your heating and hot water.