Ideal Boxer Fault codes & diagnostics

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

Combi Natural Gas 24-28 kW 1994-2005 Discontinued

Replaced by: Icos

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.
5 High 1 Medium
Just want the most common Ideal Boxer faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 6 documented codes

Tap any card for details

CH LED

Your boiler is struggling to receive the signal to start your central heating, possibly because it is not being told to turn on by your timer or thermostat.

Medium DIY-safe £100-250

What to check first

  1. Check that your heating timer or programmer is set to 'On' and the current time is correct.
  2. Ensure your room thermostat is turned up high enough to demand heat.
  3. Check your boiler's control dial is set to the heating position.

Parts commonly replaced

  • Room thermostat
  • Programmer
  • NTC Thermistor
Full explanation for CH LED
Fault led (B) illuminated

Your boiler is failing to ignite the flame it needs to heat your water or radiators due to a persistent ignition issue.

High Engineer only £150-300

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead
  • Printed Circuit Board
Full explanation for Fault led (B) illuminated
FLAME FAILURE LED

Your boiler has tried to start but could not get the fire going or keep it lit, so it has safely shut itself down.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe
Full explanation for FLAME FAILURE LED
LOW WATER SWITCH

Your boiler has stopped working because the water pressure inside the heating system has dropped too low.

High DIY-safe £0-£120

What to check first

  1. Locate the filling loop (usually a silver braided hose with valves beneath the boiler).
  2. Open the valves slowly to allow mains water into the system until the gauge reads between 1.0 and 1.5 bar.
  3. Close the valves tightly and restart the boiler.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor switch
  • Expansion vessel
Full explanation for LOW WATER SWITCH
POWER LED

Your boiler has lost all power and is currently completely turned off.

High DIY-safe £90-250

What to check first

  1. Check your home's fuse box or consumer unit to ensure the boiler circuit breaker has not tripped.
  2. Verify that the boiler's fused spur switch, usually located on the wall nearby, is switched to the on position.
  3. Ensure the boiler's internal on/off button or dial is set correctly.

Parts commonly replaced

  • Main PCB
  • On/Off switch
  • Internal fuse
Full explanation for POWER LED
RED lockout led

Your boiler has failed to start up or stay burning, so it has safely turned itself off to prevent a build-up of unburnt gas.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead
Full explanation for RED lockout led