Main MainEco Fault codes & diagnostics

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

CombiSystem Natural GasLPG 15-35 kW 2006 onwards Discontinued
GC Numbers 41-467-2441-467-2541-467-2641-467-27

Replaced by: Baxi 600 or 800 Series

Download the Main MainEco 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.
6 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
41-467-24 15 Heat ErP 2006–present
41-467-25 18 Heat ErP 2006–present
41-467-26 24 Heat ErP 2006–present
41-467-27 30 Heat ErP 2006–present
Just want the most common Main MainEco faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 10 documented codes

Tap any card for details

1 Red Flash

Your boiler is experiencing a temporary temperature reading issue and is currently trying to fix itself automatically.

Low DIY-safe £90-180

What to check first

  1. Wait 5-10 minutes to see if the boiler automatically resets itself
  2. Check that your radiators are bled and there is no trapped air in the system
  3. Ensure your boiler pressure is between 1.0 and 1.5 bar on the pressure gauge

Parts commonly replaced

  • NTC Thermistor (Temperature Sensor)
  • Flow Pipe Sensor

Related codes

Full explanation for 1 Red Flash
2 Red Flashes

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

High DIY-safe £100-£280

What to check first

  1. Check that your radiator valves are open and not turned to off or zero
  2. Ensure your system water pressure is between 1 and 1.5 bar on the pressure gauge
  3. Turn the selector switch to the reset position for five seconds and then back to your desired setting

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • NTC Temperature Sensor

Related codes

Full explanation for 2 Red Flashes
3 Green Flashes

Your boiler has briefly lost its flame and is attempting to restart itself automatically.

Medium DIY-safe £0-120

What to check first

  1. Wait for the boiler to complete its automatic restart cycle
  2. Check that other gas appliances in the home are working correctly
  3. Monitor the boiler to see if the issue persists or clears
  4. Press the reset button if the boiler enters a permanent lockout state

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve

Related codes

Full explanation for 3 Green Flashes
3 Red Flashes

Your boiler has tried to light itself several times but cannot create a flame, meaning you will not have any heating or hot water until it is reset or repaired.

High DIY-safe £90-280

What to check first

  1. Check that your gas emergency control valve is open and you have credit on your gas meter
  2. Turn the selector switch to the 'R' (Reset) position for at least five seconds
  3. Release the switch and see if the boiler initiates a successful ignition sequence

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Probe
  • Ignition Lead

Related codes

Full explanation for 3 Red Flashes
4 Green Flashes

Your boiler is temporarily struggling to talk to its internal control parts and is trying to reconnect itself.

Low DIY-safe £0-280

What to check first

  1. Wait up to 10 minutes to see if the error clears itself as designed
  2. Turn the selector switch to 'Reset' for 5 seconds and then back to its original position
  3. Switch the main electrical power to the boiler off and back on again

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Interface

Related codes

Full explanation for 4 Green Flashes
4 Red Flashes

Your boiler has detected an issue with the ventilation fan, which means it cannot safely clear exhaust fumes and will not ignite.

High Engineer only £220-450

Parts commonly replaced

  • Extractor Fan
  • Fan Wiring Harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 4 Red Flashes
5 Green Flashes

Your boiler has experienced a temporary electronic communication glitch and is attempting to sort itself out automatically.

Low DIY-safe £0-280

What to check first

  1. Wait for the boiler to complete its automatic reset process
  2. If the flashing continues for more than 15 minutes, turn the selector switch to 'Reset' for five seconds
  3. Monitor the boiler to see if the lights return to a steady green

Parts commonly replaced

  • Parameter Storage Unit (PSU)
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 5 Green Flashes
5 Red Flashes

Your boiler's internal memory chip has developed a software or connection error, meaning it can no longer remember its correct settings to operate.

High Engineer only £120-350

Parts commonly replaced

  • Parameter Storage Unit (PSU) chip
  • Printed Circuit Board (PCB)
Full explanation for 5 Red Flashes
6 Green Flashes

Your boiler is experiencing a communication error or internal electronic fault that is preventing it from running properly.

High DIY-safe £100-£350

What to check first

  1. Locate the selector switch on the front of the boiler.
  2. Turn the switch to the 'Reset' position and hold it for five seconds.
  3. Turn the switch back to the 'On' position and wait for the boiler to restart.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 6 Green Flashes
6 Red Flashes

Your boiler has detected a general internal error, often linked to a small electronic glitch or a sensor that is failing to communicate correctly with the main controls.

High DIY-safe £100-280

What to check first

  1. Locate the reset knob on the front control panel
  2. Turn the knob to the 'R' (Reset) position and hold for 5 seconds
  3. Release the knob and wait to see if the error light clears and the boiler restarts

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • Temperature sensors

Related codes

Full explanation for 6 Red Flashes
Status & diagnostic codes

1 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 break until it needs to heat up again.