Ferroli Domi Compact Fault codes & diagnostics

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

Combi Natural Gas 24-30 kW 2006-2012 Discontinued

Replaced by: DomiCondens

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.
4 Emergency 23 High 3 Medium 10 Low
Just want the most common Ferroli Domi Compact faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 40 documented codes

Tap any card for details

LED / flash-pattern codes
4 (Flashing Light)

Your boiler is perfectly healthy and is simply waiting for a signal from your thermostat to turn on the heating.

Low DIY-safe

What to check first

  1. Check your room thermostat is turned up to a temperature higher than the current room temperature
  2. Ensure your heating timer or programmer is set to 'On'
  3. Wait for the boiler to detect a request for heat and the indicator light to stabilise
Full explanation for 4 (Flashing Light)
5 (Flashing Light)

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

High DIY-safe £0-£80

What to check first

  1. Locate the filling loop (a silver flexible hose with one or two valves) underneath the boiler.
  2. Open the valve(s) slowly to allow cold mains water into the system while watching the pressure gauge.
  3. Close the valve(s) tightly once the needle reaches 1.5 bar, then turn the boiler off and on again to clear the fault.

Parts commonly replaced

  • External filling loop
  • Pressure relief valve
  • Pressure sensor

Related codes

Full explanation for 5 (Flashing Light)
LED4 Flashing

Your boiler is currently in standby mode and is simply waiting for a signal from your heating controls or hot water tap to turn on.

Low DIY-safe

What to check first

  1. Check your room thermostat is set to a higher temperature than the current room temperature.
  2. Ensure your heating timer or programmer is currently in an 'ON' period.
  3. Turn on a hot water tap to see if the boiler initiates the burner cycle.
Full explanation for LED4 Flashing
LED5 Flashing

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

High DIY-safe £0-£120

What to check first

  1. Locate the external filling loop, which is a silver braided hose connecting two pipes near the boiler.
  2. Open the small valves at both ends of the hose to allow mains water to enter the system.
  3. Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (between 1 and 1.5 bar), then close both valves tightly.

Parts commonly replaced

  • Filling loop
  • Pressure gauge
  • Pressure sensor
Full explanation for LED5 Flashing
Digital codes
5 (Permanent Light)

Your boiler is operating normally and is receiving power as expected.

Low DIY-safe

What to check first

  1. No action is required as this simply confirms the boiler is powered on and functioning correctly.
Full explanation for 5 (Permanent Light)
DOMIcondens HE 26 C

Your boiler has detected that the exhaust gases are getting too hot, causing it to shut down for safety.

High Engineer only £120-350

Parts commonly replaced

  • Main Heat Exchanger
  • Flue NTC Sensor
  • Heat Exchanger Scale Descaler

Related codes

Full explanation for DOMIcondens HE 26 C
E01

Your boiler has stopped working because it cannot light its burner, which could be due to a blocked flue or a lack of gas supply.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB
  • Flame sensor

Related codes

Full explanation for E01
E04

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

High DIY-safe

What to check first

  1. Locate the external filling loop, which is usually a silver braided hose connected between two valves under the boiler.
  2. Open the valves slowly to allow water to enter the system until the pressure gauge on the front of the boiler reads between 1 and 1.5 bar.
  3. Close both valves tightly and check the display to ensure the error code has cleared.

Parts commonly replaced

  • Filling loop
  • Pressure gauge
  • Pressure relief valve

Related codes

Full explanation for E04
F01

Your boiler has stopped working because it has failed to light the burner, meaning you currently have no heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for F01
Showing 11–20 of 40
F1

Your boiler has stopped working because it failed to ignite the gas flame required to heat your water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB
Full explanation for F1
F2

Your boiler has detected that the burner failed to light or stay lit, so it has safely shut itself down to prevent gas from escaping.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Flame sensor
  • Gas valve
  • Control board

Related codes

Full explanation for F2
F02

Your boiler is detecting a flame even though it has tried to switch itself off, which indicates a safety concern that prevents it from restarting.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flame rectification electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for F02
F3

Your boiler has detected an issue with the airflow system or flue, causing it to shut down for safety reasons.

High Engineer only £120-250

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Venturi

Related codes

Full explanation for F3
F03

Your boiler has detected that it is running much hotter than it should be and has automatically switched itself off to prevent internal damage.

High Engineer only £120-250

Parts commonly replaced

  • Pump
  • NTC thermistor
  • Heat exchanger
  • Central heating filter

Related codes

Full explanation for F03
F04

Your boiler has detected that the exhaust gases are becoming too hot, so it has safely shut itself down to prevent damage.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flue gas thermostat
  • Primary heat exchanger
  • Fan assembly

Related codes

Full explanation for F04
F5

Your boiler has detected a temporary issue with the air vent or exhaust system and is pausing itself to stay safe, but it should restart on its own once the condition clears.

Low Engineer only £100-250

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Venturi

Related codes

Full explanation for F5
F05

Your boiler is failing to detect the airflow needed for safe operation, so it has shut down to prevent the burner from lighting.

High Engineer only £120-250

Parts commonly replaced

  • Air pressure switch
  • Flue fan unit
  • Venturi tube

Related codes

Full explanation for F05
F06

Your boiler has repeatedly failed to keep its pilot light lit and has now shut itself down as a safety precaution.

High Engineer only £150-300

Parts commonly replaced

  • Flame rectification electrode
  • Gas valve
  • Ignition lead

Related codes

Full explanation for F06
F7

Your boiler has lost the ability to accurately measure the temperature of the water flowing through the system, so it has shut down to prevent damage.

High Engineer only £120-200

Parts commonly replaced

  • NTC temperature sensor
  • Wiring loom
Full explanation for F7
Showing 21–30 of 40
F07

Your boiler has detected that the exhaust gases leaving the system are getting dangerously hot, so it has shut itself down to prevent damage or fire risk.

Emergency Engineer only £150-300

Parts commonly replaced

  • Heat exchanger
  • Flue gas sensor
  • NTC probe

Related codes

Full explanation for F07
F9

Your boiler has lost the ability to detect when you turn on the hot tap, meaning your hot water will currently not fire up when needed.

Medium Engineer only £120-180

Parts commonly replaced

  • DHW NTC sensor
  • Wiring harness

Related codes

Full explanation for F9
F10

Your boiler is unable to read the temperature of the water flowing through the system, so it has turned itself off to prevent overheating.

High Engineer only £120-200

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

Full explanation for F10
F11

Your boiler is having trouble sensing the temperature of your hot water tap supply, which means it cannot provide hot water to your taps.

Medium Engineer only £120-180

Parts commonly replaced

  • DHW NTC sensor
  • Wiring harness

Related codes

Full explanation for F11
F13

Your boiler's temperature sensor is providing incorrect readings or has lost its connection, causing the system to stop working as a safety precaution.

High Engineer only £120-200

Parts commonly replaced

  • Domestic hot water temperature sensor

Related codes

Full explanation for F13
F14

Your boiler has lost the ability to detect the temperature of the water flowing through your heating system, so it has shut itself down to prevent damage.

High Engineer only £120-220

Parts commonly replaced

  • Central heating flow sensor / NTC sensor
  • Wiring harness

Related codes

Full explanation for F14
F34

Your boiler has detected that the electrical power supply is too weak to operate safely, causing it to shut down.

High Engineer only £120-250

Parts commonly replaced

  • Main PCB
  • Power supply wiring

Related codes

Full explanation for F34
F35

Your boiler has detected an issue with the electricity supply frequency, which prevents it from operating correctly.

High Engineer only £150-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for F35
F37

Your boiler has detected that the water pressure inside the system is too low, so it has temporarily turned itself off to prevent any damage.

High DIY-safe £80-120

What to check first

  1. Locate the filling loop (a silver flexi-hose with one or two valves) underneath your boiler.
  2. Open the valve(s) slowly to let water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.
  3. Ensure both valves are fully closed again to stop the water flow.

Parts commonly replaced

  • Pressure gauge
  • Filling loop
  • Pressure relief valve

Related codes

Full explanation for F37
F39

Your boiler is having trouble communicating with the outdoor weather sensor, which means it cannot automatically adjust your heating based on the outside temperature.

Low Engineer only £90-180

Parts commonly replaced

  • External temperature sensor
  • Wiring loom

Related codes

Full explanation for F39
Showing 31–40 of 40
F40

Your boiler has detected that the water pressure inside the system is currently higher than the recommended safety limit.

Medium DIY-safe £80-150

What to check first

  1. Locate a radiator in your home with a bleed valve
  2. Open the bleed valve slowly using a radiator key to let air and water escape into a container
  3. Close the valve once the internal pressure gauge on your boiler drops to the green zone (typically 1.0 to 1.5 bar)

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor/transducer
  • Filling loop

Related codes

Full explanation for F40
F41

Your boiler has detected that hot water isn't moving around your system properly, so it has shut down to prevent itself from overheating.

High Engineer only £120-250

Parts commonly replaced

  • Central Heating Pump
  • Flow switch
  • System filter

Related codes

Full explanation for F41
F43

Your boiler has detected that the water inside the system is getting too hot too fast, so it has shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • System pump
  • Temperature sensor
  • Heat exchanger

Related codes

Full explanation for F43
F47

Your boiler has lost the ability to detect your system's water pressure, so it has safely shut down to prevent potential damage.

High Engineer only £120-200

Parts commonly replaced

  • Water pressure transducer
  • Wiring harness

Related codes

Full explanation for F47
F50

Your boiler has lost its connection to the gas control component, preventing it from safely starting up to provide heat or hot water.

Emergency Engineer only £120-250

Parts commonly replaced

  • Gas valve wiring harness
  • Gas valve assembly
  • PCB

Related codes

Full explanation for F50
LED2

Your boiler has detected a safety issue and has shut itself down to prevent damage, meaning you currently have no heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PC B (Printed Circuit Board)
  • Flame sensor

Related codes

Full explanation for LED2