Ideal Classic Fault codes & diagnostics

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

Gas 2005-present
Choose your boiler type

The Classic range comes in 2 types

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

24 2 codes · 1 GC number 30 2 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 →

Severity at a glance

Each cell = one fault code. Hover to identify.
22 High 1 Medium
Just want the most common Ideal Classic faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 23 documented codes

Tap any card for details

76

Your boiler has temporarily stopped working because the electricity supply coming into your home has dropped below the safe level it needs to operate properly.

High DIY-safe Shared across the Classic range

What to check first

  1. Check if other appliances in your home are experiencing power fluctuations.
  2. Turn the boiler off at the fused spur or mains switch, wait 30 seconds, and turn it back on to reset it.
  3. Check your electricity consumer unit (fuse box) to ensure no trip switches have been partially tripped.

Related codes

Full explanation for 76
77

Your boiler has detected an internal computer system error and has safely shut down to prevent further issues.

High Engineer only £200-400 Shared across the Classic range

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for 77
78

Your boiler's main electronic control unit has not been properly recognized or set up, which stops the boiler from working safely.

High Engineer only £150-300 Shared across the Classic range

Parts commonly replaced

  • Boiler Control Card (BCC)
  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for 78
79

Your boiler has lost communication with its internal memory card, meaning it cannot run safely and has temporarily locked itself out.

High Engineer only £150-300 Shared across the Classic range

Parts commonly replaced

  • Boiler Chip Card (BCC)
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 79
80

Your boiler has detected that the electricity supply coming into your home is too low to run it safely.

Medium Engineer only £90-180 Shared across the Classic range

Parts commonly replaced

  • Main PCB
  • Internal wiring connections

Related codes

Full explanation for 80
81

Your boiler is still providing hot water, but the central heating is not turning on when it should.

High Engineer only £100-£250 Shared across the Classic range

Parts commonly replaced

  • Central heating sensor
  • diverter valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 81
82

Your boiler is providing central heating to your home, but it is not currently producing hot water for your taps and showers.

High Engineer only £150-£350 Shared across the Classic range

Parts commonly replaced

  • Diverter valve
  • Flow sensor
  • Domestic hot water thermistor

Related codes

Full explanation for 82
83

Your boiler has completely lost power and the screen is blank, meaning it is not currently working.

High DIY-safe £100-£250 Shared across the Classic range

What to check first

  1. Check that the fused spur switch supplying power to the boiler is turned on.
  2. Inspect your home's fuse box or consumer unit to see if the circuit breaker for the boiler has tripped.
  3. If the breaker has tripped, try resetting it once; if it trips again immediately, stop and call an engineer.

Parts commonly replaced

  • Fuse
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 83
C0

Your boiler's internal memory chip is not communicating correctly with the main computer, preventing the boiler from starting safely.

High Engineer only £150-250 Shared across the Classic range

Parts commonly replaced

  • Boiler Control Card (BCC)
  • Wiring harness

Related codes

Full explanation for C0
C2

Your boiler has detected a missing or disconnected internal memory chip on its main circuit board, which prevents it from operating correctly.

High Engineer only £150-300 Shared across the Classic range

Parts commonly replaced

  • Boiler Control Chip (BCC)
  • Printed Circuit Board (PCB)

Related codes

Full explanation for C2
Showing 11–20 of 23
F1

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

High DIY-safe £80-120 Shared across the Classic range

What to check first

  1. Locate the internal filling loop, which is usually a small silver lever or a braided hose under the boiler.
  2. Open the filling valve slowly until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.
  3. Close the valve tightly and check that the fault code disappears.

Parts commonly replaced

  • Pressure sensor
  • Filling loop
  • Pressure relief valve

Related codes

Full explanation for F1
F2

Your boiler is trying to start but keeps failing to keep the flame lit, so it has shut down as a safety precaution.

High Engineer only £150-300 Shared across the Classic range

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Condensate trap

Related codes

Full explanation for F2
F3

Your boiler has detected an issue with the fan that safely clears exhaust gases, preventing it from starting up for your safety.

High Engineer only £250-£450 Shared across the Classic range

Parts commonly replaced

  • Fan assembly
  • PCB (Printed Circuit Board)
  • Wiring harness

Related codes

Full explanation for F3
F4

Your boiler has detected a problem with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot safely regulate heat.

High Engineer only £100-180 Shared across the Classic range

Parts commonly replaced

  • Flow thermistor (NTC sensor)
  • Wiring harness
  • Main PCB

Related codes

Full explanation for F4
F5

Your boiler has detected a sensor problem that means it cannot accurately measure the temperature of the water returning to the unit, causing it to shut down for safety.

High Engineer only £90-180 Shared across the Classic range

Parts commonly replaced

  • Return thermistor (NTC sensor)
  • Wiring harness
  • Main PCB

Related codes

Full explanation for F5
F7

Your boiler has detected that the electrical supply coming into your home is too low for it to operate safely.

High Engineer only £100-350 Shared across the Classic range

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Voltage Regulator

Related codes

Full explanation for F7
F9

Your boiler's main computer control panel is experiencing a software or internal communication error, meaning the boiler has safely shut down to prevent incorrect operation.

High Engineer only £250-450 Shared across the Classic range

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for F9
L and 1

Your boiler has temporarily shut down because the water inside it has become too hot.

High Engineer only £150-300 Shared across the Classic range

Parts commonly replaced

  • NTC thermistor
  • Pump
  • Heat exchanger

Related codes

Full explanation for L and 1
L and 2

Your boiler has failed to light its flame after a few attempts, so it has safely shut itself down to prevent a gas build-up.

High Engineer only £90-250 Shared across the Classic range

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • PCB

Related codes

Full explanation for L and 2
L1

Your boiler has switched itself off because the internal water temperature has become too hot, usually caused by a lack of water flow through the system.

High DIY-safe £120-£350 Shared across the Classic range

What to check first

  1. Check that your radiator valves are fully open
  2. Ensure your boiler pressure is between 1 and 1.5 bar on the gauge
  3. Reset the boiler by turning the control knob to 'RE' or pressing the reset button

Parts commonly replaced

  • Circulating pump
  • Thermistor (NTC sensor)
  • Main heat exchanger

Related codes

Full explanation for L1
Showing 21–23 of 23
L2

Your boiler has failed to light several times and has shut down for safety, meaning you currently have no heating or hot water.

High DIY-safe £100-£350 Shared across the Classic range

What to check first

  1. Check if your gas supply is active by testing another gas appliance like a hob.
  2. Check if your condensate pipe (the white plastic pipe outside) is frozen or blocked.
  3. Reset the boiler by turning the control knob to 'Reset' and holding for two seconds.

Parts commonly replaced

  • Gas valve
  • Ignition electrode
  • Flame sensing probe
  • Spark generator

Related codes

Full explanation for L2
L5

Your boiler has attempted to restart itself too many times in a short period and has now locked itself out for safety.

High Engineer only £120-250 Shared across the Classic range

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board (PCB)
  • Flue seal

Related codes

Full explanation for L5
L6

Your boiler thinks a flame is burning even though it shouldn't be, causing the system to shut down for safety.

High Engineer only £120-280 Shared across the Classic range

Parts commonly replaced

  • Ionisation probe
  • Flame sensing electrode
  • Printed Circuit Board (PCB)

Related codes

Full explanation for L6
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