Ideal British Gas RD Fault codes & diagnostics

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

Regular Natural Gas 9-30 kW 2003 onwards Discontinued

Replaced by: Ideal Mexico

Choose your boiler type

The British Gas RD range comes in 6 types

Pick the one you have. The fault codes, GC numbers and manual differ by type.

RD112 3 codes · 1 GC number RD115 3 codes · 1 GC number RD118 3 codes · 1 GC number RD121 3 codes · 1 GC number RD124 3 codes · 1 GC number RD130 3 codes · 1 GC number
Each model has its own manual A family spans several manuals, one per model or generation. Pick your model above and its page has the manual its fault codes were read from.

The fault code is already on your display

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

Just want the most common Ideal British Gas RD 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 physically reset to try and start again.

High DIY-safe £120-250 Shared across the British / Scottish range

What to check first

  1. Turn the selector knob to the Reset position for 5 seconds
  2. Turn the knob back to your preferred setting
  3. Wait to see if the burner ignites and the light stops flashing

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board

Related codes

Full explanation for Lockout
Reverse polarity

Your boiler is failing to start because the electrical supply wires have been connected in the wrong order, preventing the system from safely powering up.

High Engineer only £90-150 Shared across the British / Scottish range

Parts commonly replaced

  • Main PCB
  • Electrical wiring loom
Full explanation for Reverse polarity
Sensor Faults

Your boiler has detected that a temperature monitoring sensor is providing incorrect readings or has stopped working, meaning the unit cannot safely manage its heat output.

High Engineer only £120-220 Shared across the British / Scottish range

Parts commonly replaced

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

8 operating states & engineer diagnostics

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

F2A Diagnostic Your boiler has detected an electrical problem with an internal safety fuse, which is preventing it from turning on to protect its delicate electronic components. Fan start up Status Your boiler is failing to start because it cannot properly clear away exhaust gases before igniting. LED 1 Diagnostic Your boiler has failed to ignite because it cannot detect a flame, meaning it has safely shut down to prevent gas from escaping. LED 2 Diagnostic Your boiler is simply indicating that it has successfully detected an electrical supply and is currently booting up. LED 3 Diagnostic Your boiler is currently undergoing a routine internal startup sequence as it receives power, and this light pattern simply confirms it is initializing its control system. LED 4 Diagnostic Your boiler is currently performing a routine startup check as it receives power, which is a normal part of the ignition process. Pump overrun Status Your boiler is currently running its internal pump to safely move leftover heat after the burner has turned off, which is a normal protective process. Run Status Your boiler is currently operating normally and is in its active heating mode.