Saunier Duval Furnaces Error Codes

F0

Furnace is locked out, no heating demand is served, the display shows F0, and the burner does not attempt to ignite.

Safety Lockout / Internal Control Fault

F1

The furnace displays F1 and will not start. The fan may run briefly then stop, and there is no ignition sequence.

Flow Temperature Sensor Fault (NTC Open/Short)

F10

Furnace shows F10; there is no heating, and the pump may run briefly then stop.

Flow Sensor / Flow Switch Fault

F11

Furnace displays F11; heating stops, and this may be associated with domestic hot water priority models.

DHW Flow Sensor Fault (on combi-type furnace/boiler units)

F12

Furnace shows F12; the unit may not respond to user interface commands.

User Interface / Display Board Communication Fault

F13

Furnace displays F13; heating may work intermittently, and temperature readings appear incorrect.

Outdoor Sensor Fault (if fitted) / Auxiliary NTC Fault

F14

Furnace shows F14; the burner does not start, and this may be associated with gas valve control.

Gas Valve Control Fault

F15

Furnace displays F15; the unit may shut down unexpectedly, sometimes after long operation.

Flue Gas Temperature Sensor Fault / Overtemperature

F16

Furnace shows F16, no heating; this may occur after power interruptions.

Internal EEPROM / Configuration Fault

F2

The furnace displays F2, and the burner shuts down shortly after starting or does not start. It may cycle on/off rapidly.

Return Temperature Sensor Fault (NTC Open/Short)

F20

Furnace displays F20, heating stops; the pump may continue running.

Primary Circuit Overtemperature / Flow Overheat

F22

Furnace shows F22, no heating; this may occur after draining or bleeding the system.

Dry Fire / Low Water Content Protection

F23

Furnace displays F23, heating stops; this may be accompanied by noisy operation.

Flow/Return Temperature Differential Too High

F24

Furnace shows F24; a rapid temperature rise is detected, and the unit shuts down quickly after start.

Pump Blocked / No Circulation

F25

Furnace displays F25, the burner shuts down; this may be associated with flue gas recirculation.

Flue Gas Recirculation / CO Protection

F26

Furnace shows F26, no ignition; this may occur after gas valve replacement.

Gas Valve Regulation Fault

F27

Furnace displays F27, ignition is blocked; this may occur immediately on power-up.

Flame Detection Error (False Flame Signal)

F28

Furnace shows F28: repeated ignition attempts with clicking but no flame, then lockout.

Ignition Lockout / No Gas Ignition

F29

Furnace displays F29; burner lights briefly then goes out, leading to multiple attempts before lockout.

Flame Loss During Operation

F3

The furnace displays F3 and stops, often after running for a short time. The casing may feel very hot.

Overheat Thermostat Trip / Safety Thermostat Open

F30

Furnace displays F30; no heating, potentially associated with room thermostat input.

Room Thermostat / External Control Fault

F32

Furnace displays F32; fan speed error, unit may not start or may shut down.

Fan Speed Too Low / Fan Control Fault

F37

Furnace displays F37; low system pressure warning, heating may be intermittent.

Low Water Pressure

F38

Furnace displays F38; high system pressure warning, safety valve may discharge water.

High Water Pressure

F4

The furnace displays F4, no flame is established, ignition clicks may be heard, but the burner does not light.

Ignition Failure / No Flame Detection

F41

Furnace displays F41; ignition issues, potentially related to incorrect gas type or settings.

Incorrect Gas Setting / Combustion Fault

F5

Furnace displays F5, burner shuts down; this may occur during operation rather than at startup.

Flame Loss During Operation / Flame Signal Fault

F6

Furnace shows F6; the fan may run but the burner does not light, or the unit locks out shortly after a start attempt.

Air Pressure Switch Fault / Flue Fan Safety

F7

Furnace displays F7; the fan may run continuously, but the burner does not ignite.

Fan Speed / Fan Feedback Fault

F8

Furnace shows F8; the unit may attempt to start but shuts down quickly, sometimes accompanied by gurgling noises.

Low Water Pressure / Water Pressure Sensor Fault

F9

Furnace displays F9; there is no heating, and this may occur after a power surge or wiring work.

External Sensor / Communication Fault

Symptom

Furnace display is on but unresponsive to button presses

Keypad / User Interface Failure

Symptom

Furnace does not start at all; no lights or display, completely dead.

No Power / Electrical Supply Failure

Symptom

Furnace emits a burning smell or plastic smell when running

Overheating Component / Electrical Smell

Symptom

Furnace emits a high-pitched whine or humming noise during operation

Fan or Pump Noise / Resonance

Symptom

Furnace fan runs continuously even when there is no heat demand

Fan Overrun / Control Fault

Symptom

Furnace frequently cycles on and off, resulting in short burner run times and unstable room temperature.

Short Cycling / Oversizing or Control Issue

Symptom

Furnace frequently loses pressure and needs topping up

Chronic Pressure Loss / Leak or Expansion Vessel Failure

Symptom

Furnace makes loud banging or knocking noises when starting or stopping.

Water Hammer / Thermal Expansion Noise

Symptom

Furnace runs but room never reaches set temperature, especially in cold weather

Underperformance / Sizing or Control Issue

Symptom

Furnace runs, but radiators remain cold or only lukewarm.

Poor Circulation / System Balancing Issue

Symptom

Furnace starts then shuts down after a few seconds with a loud whoosh or boom

Delayed Ignition / Burner Light-Back

Symptom

Radiators get hot but domestic hot water temperature is unstable or lukewarm (on combi-type furnace/boiler)

DHW Temperature Control / Plate Heat Exchanger Issue

Symptom

Water dripping from the flue terminal outside

Condensate / Flue Condensation Issue

Symptom

Water leaking from the bottom of the furnace casing

Internal Water Leak