Error F1 or F4 on Saunier Duval Boilers: Causes, Reset, and Solutions
The error code F1 (or F4 depending on model generation) on Saunier Duval gas boilers (such as Themafast Condens, Themaclassic, Isofast, or Semiatek) indicates a critical 'Ignition Failure or Flame Loss'. The boiler attempted startup but the burner failed to ignite or the safety sensor did not detect the flame.
Step 1: Check the Gas Supply Valve
Check the yellow gas valve handle located underneath the boiler on the central pipe. It must be turned parallel to the pipe. If gas work was recently carried out in the building, air may be trapped in the supply line.
Step 2: How to Reset Error F1 on Saunier Duval
Turn the main power selector switch to '0' (OFF), wait 5 seconds, and turn it back to 'I' (ON) or 'Eco/Comfort' mode. On digital touch interfaces, press the button with the crossed-out flame or 'Reset' icon for 3 seconds.
If the boiler ignites with a smooth blue flame, the issue was a temporary ignition delay.
Common Technical Faults Behind F1 / F4 Codes
1. Dirty or Corroded Ionization Flame Sensor: Needs light burnishing with fine emery cloth to restore micro-amp conductivity.
2. Faulty Gas Valve Stepper Motor: The modulated gas valve fails to inject gas into the manifold.
3. High-Limit Overheat Thermostat Tripped: If the heat exchanger overheated due to pump failure, the manual safety klixon tripped and must be inspected.
FAQ
What is the difference between error F1 and error F4 on Saunier Duval?
F1 typically indicates total failure to light during initial ignition, while F4 indicates unexpected flame extinction while the burner was already running.
How much does a replacement ignition electrode cost on Saunier Duval?
A genuine Saunier Duval electrode kit installed by a technician costs between €65 and €115.