Ideal Response Fault codes & diagnostics

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

Combi Natural Gas 24-30 kW 2007-2012 Discontinued

Replaced by: Logic Combi

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 →

Severity at a glance

Each cell = one fault code. Hover to identify.
12 High 1 Medium

All 13 documented codes

Tap any card for details

CH light on PCB 40 flashing

Your boiler has detected a communication problem or a fault with the sensor that controls your central heating temperature.

High Engineer only £90-180

Parts commonly replaced

  • Central Heating (CH) thermistor/sensor
  • Wiring harness
  • Main PCB
HW light on PCB 40 flashing

Your boiler has detected a fault with the temperature sensor that controls your hot water, meaning it cannot accurately measure how hot the water is.

High Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) Thermistor
  • Wiring harness
81

Your boiler is successfully heating your radiators, but it is failing to heat the water for your taps and showers.

Medium Engineer only £180-350

Parts commonly replaced

  • Diverter Valve
  • Diverter Valve Motor
  • Plate Heat Exchanger
82

Your boiler has stopped working because the internal fan, which safely helps the system breathe, is not spinning.

High Engineer only £220-£380

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Air Pressure Switch

Related codes

83

Your boiler is receiving power but cannot ignite because it isn't detecting the correct gas pressure required to start the burner.

High Engineer only £180-450

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Fan

Related codes

84

Your boiler is trying to start up but is failing to create the spark or flame needed to heat your water.

High Engineer only £120-280

Parts commonly replaced

  • Ignition electrodes
  • Spark generator
  • Ignition lead
  • Gas valve

Related codes

85

Your boiler is struggling to light or keep a flame burning correctly because the gas and air mixture isn't balanced.

High Engineer only £120-350

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Burner
LED 2 on PCB 41 lit

Your boiler is failing to ignite or stay lit, meaning you will not have any heating or hot water until the issue is resolved.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation Probe
  • Gas Valve
  • Ignition Lead
  • Printed Circuit Board (PCB)
lockout LED 2 ON

Your boiler has tried to light several times but cannot detect a flame, causing the system to shut down for safety.

High DIY-safe £120-£350

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. If you have a pre-payment meter, ensure you have credit available
  3. Check if other gas appliances in your home, such as a hob, are working correctly
  4. Press the reset button once to see if the boiler restarts

Parts commonly replaced

  • Ignition PCB
  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Probe
Low system pressure

Your boiler has stopped working because the water level inside the system has dropped too low and needs topping up.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath the boiler.
  2. Slowly open the one or two small tap handles until you hear water running.
  3. Watch the pressure gauge and close the taps firmly once it reaches between 1 and 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • Pressure relief valve
  • Expansion vessel
Mains fuse F2 on PCB 40 blown

Your boiler has lost power because an internal fuse has blown, likely caused by an electrical fault in the pump.

High Engineer only £180-350

Parts commonly replaced

  • Central heating pump
  • Glass fuse (2A)
  • Printed Circuit Board (PCB)
Mains On neon NOT lit

Your boiler has no power and is completely unresponsive, likely due to an electrical supply issue or a blown fuse.

High DIY-safe £70-160

What to check first

  1. Check if your home's main electrical consumer unit has a tripped circuit breaker
  2. Ensure the boiler's external isolation switch (fused spur) is turned on
  3. Replace the 3-amp fuse in the external isolation switch with a new one

Parts commonly replaced

  • External 3A Fuse
  • EMC Filter
  • Internal PCB Fuse
Overheat 'stat tripped

Your boiler has shut down because it detected that the water inside has become too hot, causing a safety switch to trigger.

High Engineer only £90-180

Parts commonly replaced

  • Overheat Thermostat
  • Central Heating Thermistor
  • Water Pressure Switch