Saunier Duval Xeon 120 FF Fault codes & diagnostics

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

Regular Natural Gas 35 kW 1997-2005 Discontinued

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29 High 1 Medium 1 Low

All 31 documented codes

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12

Your boiler is currently in a special setting mode used by engineers to calibrate the airflow, rather than experiencing a standard mechanical failure.

Low Engineer only £90-150
Does fan Hunt? (YES)

Your boiler is struggling to keep the air extraction fan running steadily, which is usually caused by an internal electronic brain failure.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
Does fan run? (NO)

Your boiler is failing to start because the internal component responsible for clearing exhaust gases is not receiving any power.

High Engineer only £200-400

Parts commonly replaced

  • Fan motor
  • Printed Circuit Board (PCB)
  • Wiring harness
Does main burner light? (NO)

Your boiler is failing to ignite because it is not receiving the necessary electrical signal to open the gas supply.

High Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Wiring harness
Does pilot light? (NO)

Your boiler is failing to ignite because the small flame that starts the system will not stay lit.

High Engineer only £150-250

Parts commonly replaced

  • Pilot assembly
  • Multifunctional gas valve
  • Ignition electrode
F1

Your boiler has stopped working because an internal electrical safety fuse has blown, meaning the system is currently unable to power its internal components.

High Engineer only £120-200

Parts commonly replaced

  • 1A Fuse
  • Printed Circuit Board (PCB)

Related codes

F2

Your boiler has stopped working because an internal safety fuse has blown, preventing the electronic control system from powering up.

High Engineer only £150-250

Parts commonly replaced

  • Internal PCB Fuse
  • Central Heating Pump
  • Main Control PCB

Related codes

Fan does not run

Your boiler is unable to safely move air for the combustion process, which means the unit cannot fire up to provide heating or hot water.

High Engineer only £200-350

Parts commonly replaced

  • Fan unit
  • Wiring harness
  • PCB

Related codes

Fan Hunt

Your boiler's air extraction system is struggling to maintain a steady speed, which prevents the unit from starting or running reliably.

High Engineer only £250-450

Parts commonly replaced

  • Printed circuit board
  • Fan assembly
Main burner does not light

Your boiler is failing to ignite because an internal electrical component responsible for releasing gas is not receiving a signal.

High Engineer only £180-350

Parts commonly replaced

  • Main solenoid
  • Multi-functional gas control valve

Related codes

Showing 11–20 of 31
Main burner not operating

Your boiler is failing to ignite the main flame because of a problem with the internal electronics or wiring that controls the fuel supply.

High Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

Neon 1

Your boiler has no electricity flowing to it, meaning it cannot start up to provide heating or hot water.

High DIY-safe £80-150

What to check first

  1. Check the main fuse spur switch next to the boiler is turned on
  2. Check your household consumer unit to ensure the boiler circuit breaker has not tripped
  3. Check that the plug, if present, is pushed firmly into the socket

Parts commonly replaced

  • Fused spur
  • PCB
  • Wiring harness
Neon 1 lit

Your boiler is failing to detect an electrical power supply, meaning it cannot switch on or operate your heating and hot water.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External fuse or spur
  • Wiring harness
Neon 1 lit (NO)

Your boiler is failing to detect a proper power connection, which prevents it from firing up safely.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board
  • Wiring Harness
  • Fused Spur

Related codes

Neon 1 NOT lit

Your boiler is not receiving any power, meaning it is completely turned off and cannot provide heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • PCB fuse
  • Main Printed Circuit Board (PCB)
  • Power cable
Neon 2

Your boiler has stopped working because a safety sensor has triggered a shutdown to prevent it from getting too hot.

High Engineer only £120-220

Parts commonly replaced

  • Overheat thermostat
  • Limit switch
Neon 2 lit

Your boiler has stopped heating because it has detected a heat safety issue and automatically shut down to prevent damage.

High Engineer only £120-220

Parts commonly replaced

  • Overheat thermostat
  • Limit switch

Related codes

Neon 2 lit (NO)

Your boiler has shut down because it thinks it is overheating, meaning you currently do not have heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Limit switch
Neon 2 NOT lit

Your boiler has automatically shut itself down because it detected that it is getting too hot, likely due to a flow restriction or a failing safety sensor.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • NTC sensor
  • Pump

Related codes

Neon 3

Your boiler has detected an issue with its internal air supply system, which is preventing it from igniting or staying lit.

High Engineer only £150-300

Parts commonly replaced

  • Air pressure switch
  • Printed circuit board (PCB)
  • Air pressure sensing tube

Related codes

Showing 21–30 of 31
Neon 3 lit

Your boiler is failing to confirm that the flue system is clear, which is preventing it from igniting for your safety.

High Engineer only £150-300

Parts commonly replaced

  • Printed circuit board
  • Air pressure switch
Neon 3 lit (NO)

Your boiler has stopped working because it cannot confirm that air is flowing correctly through the system to burn fuel safely.

High Engineer only £180-350

Parts commonly replaced

  • Printed circuit board
  • Air pressure switch
Neon 3 NOT lit

Your boiler is failing to clear combustion gases properly, so it has safely shut itself down to prevent any risk.

High Engineer only £150-300

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Venturi
Neon 4

Your boiler has stopped working because the main control panel is failing to send electrical power to the internal gas valve to start the heating process.

High Engineer only £200-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Neon 4 lit

Your boiler has stopped working because the internal control board is failing to send electrical power to the gas valve.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness
Neon 4 lit (NO)

Your boiler has detected an internal electrical communication error on its main control system that prevents it from starting safely.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Neon 4 NOT lit

Your boiler is failing to light the burner, meaning it cannot produce heat or hot water because it has detected an issue with the ignition process.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Pilot does not light

Your boiler is failing to ignite because the small flame that acts as a match to start the main burner will not stay lit.

High Engineer only £120-250

Parts commonly replaced

  • Pilot injector
  • Ignition electrode
  • Pilot solenoid valve

Related codes

Pump does not run

Your boiler is not circulating water because the part responsible for pushing it around is failing to start even when the boiler is asking for heat.

High Engineer only £250-450

Parts commonly replaced

  • Central Heating Pump
  • Printed Circuit Board (PCB)
Pump does not stop

Your boiler's water pump is failing to switch off after the heating has finished, which will gradually wear out the pump and may indicate an internal electrical fault.

Medium Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)
Showing 31–31 of 31
Spark does not stop

Your boiler is struggling to confirm that the pilot light has successfully ignited, causing it to keep clicking as if trying to start repeatedly.

High Engineer only £200-450

Parts commonly replaced

  • Ignition electrode
  • Printed Circuit Board (PCB)
  • Ignition lead