Main Eco Compact Fault codes & diagnostics

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

Combi Natural Gas 25-30 kW 2018 onwards
GC Number 47-467-14
Download the Main Eco Compact 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.
17 High 1 Medium 2 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
47-467-14 ECO COMPACT 25 COMBI 2018–present
Just want the most common Main Eco Compact 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

09

Your boiler has detected a minor internal communication glitch and has temporarily stopped working as a safety precaution, but it should return to normal once you reset it.

Low DIY-safe

What to check first

  1. Locate the Reset button on the front control panel.
  2. Press and hold the Reset button for approximately 3 to 5 seconds.
  3. Wait for the boiler to restart and check if the display shows normal operation.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for 09
15

Your boiler has detected a minor internal communication hiccup and requires a simple manual reset to get back up and running.

Low DIY-safe

What to check first

  1. Locate the reset button on the front control panel
  2. Press and hold the button for 3 to 5 seconds
  3. Wait for the boiler to restart and the fault code to clear from the display

Related codes

Full explanation for 15
20

Your boiler has detected an internal issue with its safety controls, causing it to stop operating to ensure your home remains safe.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • Gas valve
Full explanation for 20
28

Your boiler has detected an issue with the sensor that reads the temperature of the water flowing out of the unit, meaning it has safely shut down to prevent damage.

High Engineer only £150-250

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness
Full explanation for 28
40

Your boiler has detected an internal issue with its electrical controls or sensors, causing the system to stop working reliably.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • Temperature sensor
Full explanation for 40
103

Your boiler is struggling to communicate with an optional safety monitoring device, which is causing it to suspend operation as a precaution.

High Engineer only £120-250

Parts commonly replaced

  • Safety Assist module
  • PCB interface cable

Related codes

Full explanation for 103
104

Your boiler is having trouble communicating with an optional safety device, which is causing it to stop operating for your protection.

High Engineer only £120-250

Parts commonly replaced

  • Safety Assist module
  • Wiring harness
  • PCB

Related codes

Full explanation for 104
107

Your boiler is having trouble communicating with an optional safety device installed on your system, which is causing it to temporarily halt for protection.

Medium Engineer only £120-250

Parts commonly replaced

  • Safety Assist module
  • Wiring harness
  • Main PCB

Related codes

Full explanation for 107
109

Your boiler has detected an internal system error that is preventing it from operating correctly.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

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 down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • NTC sensor
  • Primary heat exchanger
  • Pump
  • PCB

Related codes

Full explanation for 110
Showing 11–20 of 20
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 a flexible braided hose under the boiler connected to two valves.
  2. Open the valves slowly to allow water into the system until the pressure gauge on the front of the boiler reaches between 1.0 and 1.5 bar.
  3. Ensure both valves are fully closed and check the pressure gauge to confirm it is stable.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Pressure sensor

Related codes

Full explanation for 118
125

Your boiler has detected that the water inside the unit is not circulating properly or is overheating, so it has safely shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Circulation pump
  • Flow sensor
  • Primary heat exchanger
Full explanation for 125
128

Your boiler has stopped working because it cannot maintain a stable flame to heat your water.

High Engineer only £120-250

Parts commonly replaced

  • Gas valve
  • Ignition electrode
  • Flame sensor
  • Printed Circuit Board

Related codes

Full explanation for 128
130

Your boiler has detected an issue with the temperature of the exhaust gases, which has caused it to shut down for safety.

High Engineer only £150-250

Parts commonly replaced

  • Flue gas sensor
  • NTC sensor
  • Wiring harness

Related codes

Full explanation for 130
133

Your boiler is failing to light because it cannot detect a flame, which means your heating and hot water have stopped working.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for 133
134

Your boiler has stopped working because it cannot light its internal flame or is not receiving a consistent supply of gas.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe

Related codes

Full explanation for 134
135

Your boiler is failing to light because it cannot detect a flame, meaning you currently have no heating or hot water.

High Engineer only £120-250

Parts commonly replaced

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

Related codes

Full explanation for 135
160

Your boiler is struggling to operate the internal fan component, which is preventing it from safely starting up the combustion process.

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 has detected an issue with the sensor that monitors the air or exhaust flow, causing the system to stop working as a safety precaution.

High Engineer only £150-250

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Wiring harness

Related codes

Full explanation for 321
384

Your boiler has lost communication with its internal control system, causing it to shut down for safety reasons.

High Engineer only £150-£300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 384
Status & diagnostic codes

3 operating states & engineer diagnostics

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

100 Status Your boiler is currently running at its absolute maximum heat output, likely because it is performing a diagnostic test or an initial start-up process. 304 Diagnostic Your boiler is currently running an internal software adjustment process, which usually happens after maintenance or a power reset. 312 Status Your boiler is currently running a self-cleaning process to remove trapped air from the system.
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