Ideal Classic RS Fault codes & diagnostics

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

Regular Natural Gas 1994-2002 Discontinued

Replaced by: Ideal Classic SE

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Severity at a glance

Each cell = one fault code. Hover to identify.
12 High 4 Low
Just want the most common Ideal Classic RS faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 16 documented codes

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1 PILOT WILL NOT LIGHT

Your boiler's small starter flame is failing to ignite, which prevents the main heating system from starting up.

High Engineer only £90-180

Parts commonly replaced

  • Pilot injector
  • Ignition electrode
  • HT lead
  • Gas control valve
Full explanation for 1 PILOT WILL NOT LIGHT
3 PILOT LIT, BUT NO MAINS GAS

Your boiler's small pilot flame is lit, but the main burner is failing to ignite to provide heat or hot water.

High DIY-safe £120-350

What to check first

  1. Check that your room thermostat and hot water cylinder thermostat are turned up high enough to call for heat.
  2. Ensure your heating programmer or timer is set to 'On' or 'Continuous' mode.
  3. Check your property's fuse box and the boiler's power switch to ensure there is an electrical supply.

Parts commonly replaced

  • Gas Control Valve
  • Boiler Control Box
  • Internal Thermostats
Full explanation for 3 PILOT LIT, BUT NO MAINS GAS
25

Your boiler is unable to start because the small ignition flame is not lighting, which is preventing the main burner from firing up.

High Engineer only £90-210

Parts commonly replaced

  • Pilot Injector
  • Thermocouple
  • Gas Valve
  • Ignition Electrode
Full explanation for 25
26

Your boiler's pilot light is going out as soon as you let go of the ignition button, meaning the main burner cannot start.

High Engineer only £90-180

Parts commonly replaced

  • Thermocouple
  • Gas Valve
  • Pilot injector
Full explanation for 26
27

Your boiler has started an initial pilot flame, but the main burner is failing to ignite to provide heat.

High Engineer only £120-280

Parts commonly replaced

  • Gas control valve
  • Main burner injector
  • Thermocouple
Full explanation for 27
28

Your boiler has switched itself off because it has become too hot inside, likely due to a circulation problem or a component failure.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the system water pressure is at roughly 1.5 bar
  3. Once the boiler has cooled down, press the overheat reset button located on the controls

Parts commonly replaced

  • Overheat Thermostat
  • Central Heating Pump
  • Thermistor
Full explanation for 28
52

Your boiler's small pilot flame is failing to stay on, which prevents the system from firing up to provide heating or hot water.

High Engineer only £90-180

Parts commonly replaced

  • Thermocouple
  • Gas Valve
  • Pilot injector
Full explanation for 52
53

Your boiler's small pilot light is working, but the main burner is failing to ignite to provide heat or hot water.

High Engineer only £120-280

Parts commonly replaced

  • Gas Valve
  • Solenoid
  • Control PCB
Full explanation for 53
BOILER OVERHEAT THERMOSTAT

Your boiler has switched itself off completely because it has gotten too hot, which is a safety feature designed to prevent damage.

High DIY-safe £90-180

What to check first

  1. Check that all radiator valves are fully open to allow water to flow.
  2. Wait 30 minutes for the boiler to cool down completely.
  3. Press the small reset button located on the overheat thermostat (usually found behind the front bottom panel).

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Thermistor
Full explanation for BOILER OVERHEAT THERMOSTAT
Loss of system water pressure

Your boiler is losing the water pressure it needs to work properly, which usually means there is a leak somewhere in your radiators, pipes, or the boiler itself.

High DIY-safe £100-350

What to check first

  1. Check all visible radiator valves and pipework for signs of dampness or drips
  2. Locate your filling loop (usually a silver flexible hose) and carefully turn the valves to top up the pressure back to 1.5 bar
  3. Monitor the pressure gauge over the next 24 hours to see if the needle drops again

Parts commonly replaced

  • Automatic Air Vent
  • Expansion Vessel
  • Pressure Relief Valve
  • Radiator Valve Tails
Full explanation for Loss of system water pressure
Neon 1

Your boiler has detected that the internal fan system is already running or the air sensor is stuck before it should be, preventing the boiler from starting its ignition sequence safely.

High Engineer only £120-240

Parts commonly replaced

  • Air pressure switch
  • Fan assembly
  • Venturi tube

Related codes

Full explanation for Neon 1
Neon 2

Your boiler is receiving a signal from your thermostat to provide heating, so this light simply indicates it is currently in operation.

Low DIY-safe

What to check first

  1. Check your room thermostat to see if it is set higher than the current room temperature
  2. Ensure the boiler's temperature control knob is turned up
  3. Wait for the boiler to reach temperature; the light is part of normal operation

Related codes

Full explanation for Neon 2
Neon 3

Your boiler is receiving power and is currently on standby or operating normally.

Low DIY-safe

What to check first

  1. Check that your room thermostat is turned up
  2. Ensure your programmer or timer is set to an 'on' period
  3. Verify that the boiler thermostat knob is not set to the 'off' position

Related codes

Full explanation for Neon 3
Neon I3

Your boiler is receiving power and is ready to operate, as the 'I3' light simply indicates that the mains electricity is switched on.

Low DIY-safe

What to check first

  1. Check that your room thermostat is turned up to see if the boiler fires.
  2. Ensure the programmer/timer is set to 'On' or 'Auto'.
  3. No action is required if the boiler is working correctly, as this is a status indicator rather than a fault.
Full explanation for Neon I3
Neon SG1

This light simply shows that your boiler is currently trying to light its flame and should turn off once it succeeds.

Low DIY-safe

What to check first

  1. Check if your gas supply is turned on at the meter
  2. Ensure the thermostat is turned up high enough to call for heat
  3. Wait up to 30 seconds for the light to turn off once the flame is established
Full explanation for Neon SG1
Overheat thermostat lockout

Your boiler has switched itself off completely to prevent it from getting too hot and causing damage.

High DIY-safe £90-180

What to check first

  1. Wait for the boiler to cool down completely (at least 15-20 minutes).
  2. Locate the reset button on the overheat thermostat, often found on the underside or behind the front panel controls.
  3. Press the reset button and relight the pilot light following the instructions on the boiler's drop-down door.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Thermocouple
Full explanation for Overheat thermostat lockout