Ferroli iBoiler 28 Fault codes & diagnostics

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

Combi Natural Gas 28 kW 2019-present

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Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 49 High 1 Medium 1 Low
Just want the most common Ferroli iBoiler 28 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 52 documented codes

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A01

Your boiler has failed to light, which means you currently have no heating or hot water because the system cannot create a flame.

High DIY-safe £90-280

What to check first

  1. Check that your gas supply is turned on and that other gas appliances in your home are working.
  2. If you have a prepaid gas meter, ensure you have active credit.
  3. Press the Reset button on the boiler control panel for 3-5 seconds to see if the system restarts.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead

Related codes

Full explanation for A01
A02

Your boiler is trying to start up but cannot detect a flame, which is likely caused by a faulty internal sensor or a control board error.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation electrode
  • Ignition cable
  • Printed Circuit Board (PCB)

Related codes

Full explanation for A02
A03

Your boiler has stopped working because it is overheating, often due to trapped air or a lack of water moving through the system.

High DIY-safe £100-£250

What to check first

  1. Check the pressure gauge and top up to 1.5 bar if it is too low
  2. Bleed all radiators to remove trapped air from the system
  3. Ensure the central heating valves under the boiler are fully open
  4. Turn the boiler off and on again to reset the fault

Parts commonly replaced

  • Heating temperature sensor (NTC)
  • Circulation pump
  • Automatic air vent

Related codes

Full explanation for A03
A04

Your boiler has shut down because it has detected a recurring issue with how it clears exhaust gases, which has happened several times in the last day.

High Engineer only £120-350

Parts commonly replaced

  • Fan
  • Air pressure switch
  • Flue seals
  • Venting pipes

Related codes

Full explanation for A04
A05

Your boiler has detected a problem with the fan that safely removes exhaust gases, meaning it has shut down for safety.

High Engineer only £180-£350

Parts commonly replaced

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

Related codes

Full explanation for A05
A06

Your boiler is struggling to keep a flame lit because it isn't receiving enough gas or the gas pressure is too low.

High Engineer only £100-250

Parts commonly replaced

  • Gas valve
  • Gas pressure regulator
  • Ignition electrode

Related codes

Full explanation for A06
A09

Your boiler has detected a problem with how it controls the gas flow, meaning it cannot light safely and has shut down to protect your home.

High Engineer only £180-£350

Parts commonly replaced

  • Gas Valve
  • Control PCB
  • Wiring Harness

Related codes

Full explanation for A09
A14

Your boiler has shut down because it has detected a problem with how exhaust gases are being removed from the flue.

Emergency Engineer only £120-350

Parts commonly replaced

  • Flue pressure switch
  • Fan
  • Venturi tube
  • Flue seals

Related codes

Full explanation for A14
A15

Your boiler has stopped working because it has detected a recurring issue with how it clears exhaust fumes, leading it to shut down for safety.

High Engineer only £120-£280

Parts commonly replaced

  • Air pressure switch
  • Venturi tube
  • Fan assembly

Related codes

Full explanation for A15
A16

Your boiler has detected a problem with how it controls the gas supply, meaning it cannot safely ignite to provide heating or hot water.

High Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Control PCB
  • Wiring harness

Related codes

Full explanation for A16
Showing 11–20 of 52
A23

Your boiler's internal computer has become confused or has been programmed with the wrong settings, preventing it from operating correctly.

High Engineer only £90-180

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Control Card

Related codes

Full explanation for A23
A24

Your boiler's internal computer has become confused by its own settings and needs to be reconfigured by a professional to talk to the components correctly.

High Engineer only £90-180

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Display PCB

Related codes

Full explanation for A24
A41

Your boiler has stopped working because it cannot communicate with the internal sensor that monitor water temperature as it flows through the system.

High Engineer only £100-220

Parts commonly replaced

  • Flow temperature sensor (NTC)
  • Sensor wiring harness
  • Control board

Related codes

Full explanation for A41
A42

Your boiler has detected a problem with the internal sensor that monitors water temperature moving through the system, meaning it cannot safely manage your heating or hot water.

High Engineer only £120-£190

Parts commonly replaced

  • NTC Flow Sensor
  • Wiring harness

Related codes

Full explanation for A42
A54 – A55 – A63

Your boiler’s internal control computer has developed a technical error and can no longer communicate with the rest of the unit, causing the system to shut down.

High Engineer only £250-£450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for A54 – A55 – A63
A61

Your boiler's main internal computer has developed a serious electronic fault and is unable to manage the system correctly.

High Engineer only £280-450

Parts commonly replaced

  • ABM03B Main PCB
  • Control Board

Related codes

Full explanation for A61
A62

Your boiler has lost the internal connection between its main computer and the gas control unit, meaning it cannot safely light the flame.

High Engineer only £180-450

Parts commonly replaced

  • Gas valve
  • Main PCB
  • Wiring harness

Related codes

Full explanation for A62
A63 / A64 / F66

Your boiler's internal computer has developed a technical fault and can no longer communicate with the rest of the system, causing it to shut down for safety.

High Engineer only £250-£450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • ABM03B Controller Unit

Related codes

Full explanation for A63 / A64 / F66
A64

Your boiler has been manually reset too many times in a short period and has permanently locked itself out for safety.

High Engineer only £100-250

Parts commonly replaced

  • Main Control PCB
  • Ignition Electrode
  • Gas Valve

Related codes

Full explanation for A64
Boilers

Your boiler has failed to ignite or stay lit, meaning your heating and hot water have stopped working.

High DIY-safe £120-350

What to check first

  1. Check if your gas supply is active by testing another gas appliance like a hob.
  2. Press the Reset button on the control panel for five seconds.
  3. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB (Main Circuit Board)

Related codes

Full explanation for Boilers
Showing 21–30 of 52
DOMIcondens HE 26 C

Your boiler has stopped working because its internal temperature has become too high, causing it to shut down for safety.

High DIY-safe £120-280

What to check first

  1. Locate the reset button on the boiler control panel.
  2. Press and hold the reset button for at least 5 seconds.
  3. Wait for the boiler to restart; if the code persists, ensure all radiator valves are open and the system pressure is between 1 and 1.5 bar.

Parts commonly replaced

  • High limit thermostat
  • Circulation pump
  • Heat exchanger (cleaning or replacement)

Related codes

Full explanation for DOMIcondens HE 26 C
F04

Your boiler's internal computer has been set up with the wrong configuration details and cannot operate correctly.

High Engineer only £90-180

Parts commonly replaced

  • Main PCB (Control Board)
  • Parameter Key

Related codes

Full explanation for F04
F05

Your boiler has detected an issue with how it is venting waste gases, preventing it from starting up safely.

High Engineer only £100-£280

Parts commonly replaced

  • Air pressure switch
  • Venturi tube
  • Flue baffle
  • Fan

Related codes

Full explanation for F05
F07

Your boiler has detected that a internal air sensor is stuck in the wrong position, preventing the fan from starting safely to clear exhaust fumes.

High Engineer only £120-£240

Parts commonly replaced

  • Air Pressure Switch
  • Venturi Tube
  • Fan Assembly

Related codes

Full explanation for F07
F07 – F14 – A07

Your boiler has detected that the exhaust gases are getting too hot, which has caused the system to shut down for safety.

High Engineer only £120-£350

Parts commonly replaced

  • Flue gas sensor
  • Main heat exchanger
  • Primary thermistor

Related codes

Full explanation for F07 – F14 – A07
F08 – A08

Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.

High DIY-safe £120-£350

What to check first

  1. Check that your radiator valves are fully open to allow water to flow
  2. Ensure there is enough water pressure in the system by checking the gauge
  3. Press the Reset button on the control panel to see if the fault clears

Parts commonly replaced

  • Overheat Thermostat
  • Central Heating Temperature Sensor (NTC)
  • Circulation Pump

Related codes

Full explanation for F08 – A08
F09 – A09

Your boiler has shut down because it has detected that the water inside has become dangerously hot.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open to allow water to flow
  2. Ensure there is enough pressure in the system by checking the gauge
  3. Press the Reset button on the control panel to see if the fault clears

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Heat Exchanger

Related codes

Full explanation for F09 – A09
F10

Your boiler has lost its connection to the temperature sensor that monitors the water being sent to your radiators, meaning it cannot heat your home or hot water safely.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Delivery Sensor (NTC)
  • Sensor Wiring Harness

Related codes

Full explanation for F10
F10 – A10

Your boiler's internal sensor that detects water flow has stopped working properly, meaning the system doesn't know when to turn the heat on or off.

High Engineer only £120-190

Parts commonly replaced

  • NTC flow sensor
  • Wiring harness
  • Main circuit board

Related codes

Full explanation for F10 – A10
F11

Your boiler is struggling to accurately measure the temperature of your hot water, which usually means your taps will only run cold.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW Temperature Sensor (NTC)
  • Sensor Wiring Harness

Related codes

Full explanation for F11
Showing 31–40 of 52
F11 – A11

Your boiler has detected an issue with the sensor that monitors the temperature of the water coming back into the system, causing the boiler to stop working for safety.

High Engineer only £90-160

Parts commonly replaced

  • Return NTC Temperature Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for F11 – A11
F12

Your boiler is having trouble measuring the temperature of your hot water, which usually means your taps will only run cold.

High Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) thermistor
  • NTC sensor wiring harness

Related codes

Full explanation for F12
F13

Your boiler has detected a problem with a temperature sensor that monitors the main heat exchanger, preventing it from heating your water safely.

High Engineer only £90-160

Parts commonly replaced

  • NTC Temperature Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for F13
F13 – A13

Your boiler has detected an issue with the sensor that monitors exhaust gases, and it has shut down as a safety precaution.

High Engineer only £120-220

Parts commonly replaced

  • Flue gas NTC sensor
  • Wiring harness
  • Electronic Control Board (PCB)

Related codes

Full explanation for F13 – A13
F14

Your boiler's internal temperature sensor is failing to communicate correctly, preventing the system from gauging how hot the water is.

High Engineer only £90-160

Parts commonly replaced

  • Flow temperature NTC sensor
  • Wiring harness connectors

Related codes

Full explanation for F14
F15

Your boiler has stopped working because the fan that removes waste gases is either blocked by debris or is having some electrical difficulty communicating with the main system.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Fan wiring harness
  • PCB

Related codes

Full explanation for F15
F34

Your boiler is not receiving enough electrical power from the property's mains supply to operate safely and has shut down to protect its internal electronics.

High Engineer only £90-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Voltage Regulator
  • In-line Transformer

Related codes

Full explanation for F34
F35

Your boiler has detected an issue with the quality of your home's electrical supply, meaning the power entering the unit is unstable.

High Engineer only £120-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Mains Filter

Related codes

Full explanation for F35
F37

Your boiler has stopped working because the water pressure is too low and needs to be topped up.

High DIY-safe £0-150

What to check first

  1. Locate the filling loop (usually a silver braided hose with small valves) underneath the boiler.
  2. Slowly open both valves until you hear water entering the system.
  3. Watch the pressure gauge and close the valves tightly once it reaches between 1 and 1.5 bar.

Parts commonly replaced

  • Water pressure switch
  • Filling loop valve

Related codes

Full explanation for F37
F39

Your boiler has lost connection with its outdoor temperature sensor, which helps it run more efficiently based on the weather.

Low DIY-safe £70-130

What to check first

  1. Check if the boiler operates normally for heating and hot water despite the code
  2. Press the Reset button on the control panel to clear the temporary error
  3. If the code persists, contact a professional to check the external sensor wiring

Parts commonly replaced

  • External temperature probe
  • Sensor wiring

Related codes

Full explanation for F39
Showing 41–50 of 52
F41

Your boiler has shut down because the water is heating up far too quickly, often meaning it isn't flowing through the system properly.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the external system valves (isolation valves) under the boiler are in the open position
  3. Check if the central heating pump is making unusual noises or feels excessively hot

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger (if blocked with sludge)
  • NTC Temperature Sensors

Related codes

Full explanation for F41
F42 – A42

Your boiler has detected an inconsistent temperature reading between its internal sensors and has shut down to prevent overheating.

High Engineer only £120-240

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Connecting wiring loom

Related codes

Full explanation for F42 – A42
F43

Your boiler has stopped itself from overheating because the water isn't moving around the system properly or there is an air pocket trapped inside.

High DIY-safe £100-£350

What to check first

  1. Check that your system pressure is between 1 and 1.5 bar on the gauge
  2. Bleed your radiators to remove any trapped air
  3. Ensure all radiator valves and external isolation valves are fully open
  4. Reset the boiler using the 'R' button

Parts commonly replaced

  • Circulating Pump
  • Main Heat Exchanger
  • Automatic Air Vent

Related codes

Full explanation for F43
F50

Your boiler's main internal computer has developed a fault and can no longer communicate with the rest of the system.

High Engineer only £250-£400

Parts commonly replaced

  • DBM23B Circuit Board (PCB)
  • Wiring harness connectors

Related codes

Full explanation for F50
F51

Your boiler's main internal computer has developed a fault and can no longer control the heating or hot water safely.

High Engineer only £250-£450

Parts commonly replaced

  • Main Control Board (PCB)
  • DBM23B Controller

Related codes

Full explanation for F51
F52

Your boiler has lost its ability to accurately measure the temperature of the water leaving the unit, meaning it will likely shut down to prevent overheating.

High Engineer only £95-170

Parts commonly replaced

  • NTC Flow Temperature Sensor
  • Sensor wiring harness

Related codes

Full explanation for F52
F56 – A56

Your boiler is struggling to set its burner to the correct efficiency and has failed its internal setup process.

High DIY-safe £90-280

What to check first

  1. Press the Reset button on the control panel to prompt a new calibration cycle
  2. Ensure your gas supply is active and hasn't been interrupted
  3. Check that the condensate pipe is not frozen if it is currently cold outside

Parts commonly replaced

  • Gas Valve
  • Spark Electrode
  • Control PCB

Related codes

Full explanation for F56 – A56
F61 – A61

Your boiler's main internal computer has developed a communication fault and can no longer control the heating process safely.

High Engineer only £280-450

Parts commonly replaced

  • Main PCB (AGC01)
  • Wiring Harness

Related codes

Full explanation for F61 – A61
F66

Your boiler’s main control board has detected an internal electronic error and can no longer communicate with its own components properly.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for F66
F67

Your boiler's main control board has detected an internal electronic error, which is preventing the system from operating safely.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for F67
Showing 51–52 of 52
F68 – A68

Your boiler has lost communication with its internal ID chip, which acts like its brain, causing the unit to stop working for safety reasons.

High Engineer only £120-250

Parts commonly replaced

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

Related codes

Full explanation for F68 – A68
OPTIMAX HE PLUS 38C

Your boiler has failed to ignite, meaning it tried to start but couldn't light the gas flame to provide heating or hot water.

High DIY-safe £120-300

What to check first

  1. Check if your gas supply is turned on at the meter
  2. If you have a prepaid gas meter, check that you have sufficient credit
  3. Press the 'Reset' button on the boiler control panel for 3 seconds

Parts commonly replaced

  • Ignition electrode
  • Flame sensing electrode
  • Gas valve

Related codes

Full explanation for OPTIMAX HE PLUS 38C