Common problems guide

The most common Ideal RD2 problems

The faults most likely to send a Ideal RD2 into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
8 documented codes
6 most common
3 DIY-safe checks
3 engineer needed

The 6 most common faults

01
Lock-out High DIY-safe

Your boiler has safely shut itself down to prevent a potential hazard and needs to be manually reset to get working again.

What to try first

Locate the reset button or turn the mode dial on the front of your boiler to the reset position.Hold the reset button down for about 3 to 5 seconds, then release it.Wait to see if the boiler fires up normally; if the fault immediately returns, do not keep resetting it.

Parts
Ignition lead, Electrodes, Gas valve
Full guide for Lock-out
02
Fan start up High Engineer

Your boiler is failing to start up because the internal fan is not operating correctly.

Est. cost
£150-300
Parts
Fan assembly, PCB
Full guide for Fan start up
03
Sensor Faults High Engineer

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

Est. cost
£120-220
Parts
NTC Sensor, Wiring harness
Full guide for Sensor Faults
04
Reverse polarity High Engineer

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

Est. cost
£90-150
Parts
External electrical supply wiring, Fused spur
Full guide for Reverse polarity
05
Control 'stat open circuit or waiting for demand Medium DIY-safe

Your boiler is currently paused because your home thermostat is either not sending a signal to turn on or is set below the current room temperature.

What to try first

Check your main room thermostat to ensure the target temperature is set higher than the current room temperature.Replace the batteries in your wireless wall thermostat if it has a digital display.Turn the boiler off at the mains power switch, wait 30 seconds, and turn it back on to reset the system.

Est. cost
£80-150
Parts
Room thermostat, Wireless receiver
Full guide for Control 'stat open circuit or waiting for demand
06
Application of power Low DIY-safe

Your boiler is simply indicating that electrical power has just been applied to it, which is a normal startup status rather than an actual fault.

What to try first

Wait a moment to see if the boiler transitions to normal operation automatically.If the boiler remains stuck on this startup indicator, try turning the main power switch off and on again to reset it.

Full guide for Application of power
Parts most often replaced

on the Ideal RD2

Ignition leadElectrodesGas valvePrinted Circuit Board (PCB)Fan assemblyPCB

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Ideal shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
See the full 8-code list for the Ideal RD2

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →