Ideal Classic FF Fault codes & diagnostics

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

Regular Natural Gas 10-24 kW 1997-2005 Discontinued
GC Number 41-349-71

Replaced by: Ideal Classic SE

Download the Ideal Classic FF manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Just want the most common Ideal Classic FF faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 4 documented codes

Tap any card for details

LED / flash-pattern codes
PCB 38 CH light flashing

Your boiler has detected a communication issue or a component failure within its central heating temperature sensing system, meaning it cannot accurately monitor the water temperature for your radiators.

Medium Engineer only £110-190

Parts commonly replaced

  • Central Heating (CH) Thermistor
  • Wiring Harness
  • Control PCB
Full explanation for PCB 38 CH light flashing
PCB 38 HW light flashing

Your boiler's hot water sensor is struggling to communicate with the main control board, meaning the system cannot accurately monitor the water temperature.

High Engineer only £120-190

Parts commonly replaced

  • Domestic Hot Water (DHW) Thermistor
  • Wiring Harness
  • Main PCB
Full explanation for PCB 38 HW light flashing
Digital codes
Low system pressure neon lit

Your boiler has detected that there is not enough water in the central heating system to operate safely, so it has shut down to protect itself.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop, which is usually a flexible silver hose with two small valves underneath the boiler.
  2. Slowly open both valve handles until you hear water entering the system.
  3. Watch the pressure gauge and close both valves tightly once the needle reaches 1.5 bar.

Parts commonly replaced

  • External filling loop
  • Expansion vessel
  • Pressure relief valve
Full explanation for Low system pressure neon lit
Mains On neon not lit

Your boiler has no power, which means it cannot turn on to provide heating or hot water.

High DIY-safe £90-180

What to check first

  1. Check if other appliances are working to rule out a general power cut
  2. Check your home fuse box for any tripped switches
  3. Ensure the boiler's power switch or fused spur next to the boiler is turned on

Parts commonly replaced

  • EMC filter
  • Internal fuse
  • Main PCB
Full explanation for Mains On neon not lit
Status & diagnostic codes

3 operating states & engineer diagnostics

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

LED2 on PCB 37 Status Your boiler is trying to light but the flame is cutting out almost immediately, which is usually caused by a dirty sensor or a problem with the gas supply. LED3 on PCB 37 Status This light is actually a positive signal showing that your boiler's internal electrical fuse is working correctly and the control board has power. Neon SG Status Your boiler is currently trying to light the gas burner with a spark, but it is failing to sense a flame and stay on.