Ideal RD2 Fault codes & diagnostics

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

Regular Natural Gas 11-23 kW 2001 onwards Discontinued
GC Numbers 41-392-7241-392-7341-397-56

Replaced by: Classic

Download the Ideal RD2 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
41-392-72 RD2 4100 2001–present
41-392-73 RD2 4125 2001–present
41-397-56 RD109 2003–present
Just want the most common Ideal RD2 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 3 documented codes

Tap any card for details

Lockout

Your boiler has stopped working for safety reasons and needs to be restarted, but if the issue keeps happening, a professional will need to investigate.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB
Full explanation for Lockout
Reverse polarity

Your boiler is failing to start because the electrical supply wires have been connected the wrong way around.

High Engineer only £90-150

Parts commonly replaced

  • External electrical supply wiring
  • Fused spur
Full explanation for Reverse polarity
Sensor Faults

Your boiler has detected an issue with one of its internal heat sensors and has stopped working to ensure safety.

High Engineer only £120-220

Parts commonly replaced

  • NTC Sensor
  • Wiring harness
Full explanation for Sensor Faults
Status & diagnostic codes

2 operating states & engineer diagnostics

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

LED 3 Diagnostic Your boiler is currently experiencing a sensor error or electrical fault that is preventing it from operating correctly. LED 4 Diagnostic Your boiler is signalling an electrical wiring issue or a faulty thermostat connection, which is preventing it from communicating correctly to start your heating or hot water.