Main Combi 30 HE Fault codes & diagnostics

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

Combi Natural Gas 30 kW 2005-2012 Discontinued
GC Number 47-474-03

Replaced by: Main Eco Elite

Download the Main Combi 30 HE 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 →

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
47-474-03 Combi 30 HE 2005–2012
Fault codes

All 2 documented codes

Tap any card for details

10

Your boiler has lost the ability to accurately measure the temperature of the hot water, so it has shut down to prevent overheating.

High Engineer only £120-180

Parts commonly replaced

  • DHW NTC Sensor
Full explanation for 10
E66

Your boiler is struggling to direct heat correctly between your radiators and your hot water taps, likely due to a stuck internal component or a sensor reading error.

High Engineer only £180-350

Parts commonly replaced

  • 3-Way Diverter Valve
  • Safety Thermostat
  • Pressure Gauge
Full explanation for E66
Status & diagnostic codes

10 operating states & engineer diagnostics

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

24 Status Your boiler has stopped working because it cannot light its burner properly, which is often due to a blockage in the internal waste pipe that clears away water created during heating. 25 Status Your boiler has detected that it is overheating and has automatically shut down to prevent damage or dangerous conditions. 26 Status Your boiler is struggling to clear air properly, meaning it has safely shut itself down to prevent any harmful combustion gases from lingering. 27 Status Your boiler is struggling because it either cannot circulate water correctly or there is not enough water pressure inside the system to operate safely. 28 Status Your boiler is struggling to detect the temperature of the water it is trying to heat for your taps and shower. 29 Status Your boiler has stopped working because it is unable to accurately measure the temperature of the water used for your radiators. 30 Status Your boiler is simply performing its normal startup routine and is currently initializing its internal systems. 31 Status Your boiler is struggling to detect or regulate the flow of hot water, which may result in your taps running cold. 32 Status Your boiler has detected an issue with the central heating system, which is currently preventing your radiators from heating up. 33 Status Your boiler is operating normally and is currently firing the burner to provide heating or hot water.