Main Eco Compact System Fault codes & diagnostics

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

System Natural Gas 25-30 kW 2018 onwards
GC Number 41-467-30
Download the Main Eco Compact System manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
14 High 3 Medium
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
41-467-30 ECO COMPACT 15 SYSTEM 2018–present
Just want the most common Main Eco Compact System faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 17 documented codes

Tap any card for details

09

Your boiler has detected an internal error that has caused it to stop working, and it needs to be restarted to attempt to clear the fault.

High DIY-safe £100-250

What to check first

  1. Locate the 'Reset' button on the boiler control panel.
  2. Press and hold the button for 2-3 seconds.
  3. Wait a few minutes to see if the boiler ignites and the fault code clears.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • Gas valve
Full explanation for 09
15

Your boiler has encountered a temporary error and needs a simple restart to try and get things back to normal.

Medium DIY-safe £80-150

What to check first

  1. Locate the reset button on your boiler control panel.
  2. Press and hold the button for 3 to 5 seconds.
  3. Wait a few minutes to see if the boiler restarts and the error code clears.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for 15
20

Your boiler has detected that the water pressure inside the system is too low for it to operate safely and efficiently.

High DIY-safe £0-£80

What to check first

  1. Locate the external filling loop, which is a silver braided hose with one or two small valves connecting your cold mains pipe to your heating pipes.
  2. Open the valve(s) slowly to allow water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.
  3. Close the valve(s) tightly and restart the boiler to clear the error.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Pressure sensor

Related codes

Full explanation for 20
28

Your boiler has detected an issue with the sensor that reads the temperature of the water, which prevents it from heating up correctly.

High Engineer only £150-250

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring Harness
Full explanation for 28
40

Your boiler has detected an issue with the water pressure or the flow sensor, which is preventing it from heating your home or water reliably.

High Engineer only £150-300

Parts commonly replaced

  • Flow sensor
  • Pressure sensor
  • Wiring harness

Related codes

Full explanation for 40
109

Your boiler has detected that the water pressure inside the system is far too high for it to operate safely.

Medium DIY-safe £90-180

What to check first

  1. Locate the filling loop under the boiler, which is usually a small silver braided hose with one or two valves.
  2. Ensure both ends of the filling loop are firmly closed, as a leaking valve is the most common cause of rising pressure.
  3. If the pressure remains high, vent (bleed) one of your radiators slightly to release excess water until the boiler pressure gauge drops to the green zone (typically 1.0 to 1.5 bar).

Parts commonly replaced

  • Filling loop valves
  • Pressure relief valve (PRV)
  • Expansion vessel

Related codes

Full explanation for 109
110

Your boiler has detected that the water inside the unit is getting too hot and has automatically shut itself down to prevent damage or overheating.

High Engineer only £120-250

Parts commonly replaced

  • NTC temperature sensor
  • Central heating pump
  • Plate heat exchanger

Related codes

Full explanation for 110
118

Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.

High DIY-safe £80-150

What to check first

  1. Locate the external filling loop, which is usually a flexible silver hose connected to the pipes underneath your boiler.
  2. Open the valves at both ends of the filling loop to allow cold mains water into the system.
  3. Watch the pressure gauge on the front of the boiler and close the valves once the needle reaches the green zone, typically between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Expansion vessel
Full explanation for 118
125

Your boiler is failing to detect the expected rise in temperature after the burner fires up, indicating it cannot effectively transfer heat into your system.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • Diverter valve
  • Flow sensor
  • Primary heat exchanger

Related codes

Full explanation for 125
128

Your boiler has stopped because the flame inside has gone out and it cannot get it to stay lit.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe

Related codes

Full explanation for 128
130

Your boiler has detected that the temperature of the water inside the system has risen too quickly, causing it to shut down to prevent damage.

High Engineer only £150-250

Parts commonly replaced

  • NTC sensor
  • Pump
  • Primary heat exchanger

Related codes

Full explanation for 130
133

Your boiler is currently unable to light the burner, which means it cannot produce any heat or hot water.

High DIY-safe £120-250

What to check first

  1. Check your gas meter to ensure the supply is on and you have credit if using a pre-payment meter.
  2. Ensure any other gas appliances in your home, such as a hob, are working to confirm gas is reaching the property.
  3. Press the 'Reset' button on the boiler control panel once to see if it successfully re-ignites.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB (Printed Circuit Board)

Related codes

Full explanation for 133
134

Your boiler has stopped working because it cannot light the flame required to produce heat.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for 134
135

Your boiler has stopped working because it cannot light the internal flame, which is often caused by a blocked gas supply, a power issue, or a faulty ignition component.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB (Printed Circuit Board)

Related codes

Full explanation for 135
160

Your boiler's fan system is not responding correctly, which means the unit has shut itself down to prevent unsafe operation.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 160
321

Your boiler is struggling to read its own temperature sensor, which has caused it to stop working to ensure safety.

High Engineer only £150-250

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness
  • Printed Circuit Board

Related codes

Full explanation for 321
384

Your boiler has detected an internal communication error and needs to be restarted to clear the fault.

Medium DIY-safe £100-200

What to check first

  1. Locate the 'Reset' button on the boiler control panel
  2. Press and hold the reset button for 3 to 5 seconds
  3. Wait 2 minutes to see if the boiler resumes normal operation

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for 384
Status & diagnostic codes

3 operating states & engineer diagnostics

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

18 Diagnostic Your boiler has detected an issue with the gas flow or combustion process and has shut down to ensure safety. G20 Diagnostic Your boiler has detected that the fuel type it is configured to use does not match the gas supply, meaning it will not safely ignite. IPX5D Diagnostic This code is not actually an error message, but an official label on your boiler casing indicating that the unit is built to withstand water splashes and humidity.
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