What does the fault code F2 mean on Saunier Duval?

Safety Flue Test (SFT) / air pressure switch fault. If the pressure switch does not activate on start-up, the PCB detects a lack of flue depression and locks out due to SFT. Check silicone tubes/venturi and the switch operation by applying controlled depression and measuring continuity at the contacts.

What does the fault code F33 mean in Saunier Duval?

Airflow fault due to open/defective air pressure switch. The pressure switch contact remains open or stuck, preventing draft validation. Check with a vacuum pump/manometer and multimeter the triggering pressure and the closing/opening; inspect the venturi, flue duct, and fan to rule out obstructions.

RefurbishedSaunier Duval Pressure switches

Saunier Duval Air Pressure Switch SD 623 Ref. 05156000

Name: Saunier Duval Air Pressure Switch SD 623 Ref. 05156000
Brand: Saunier Duval
SKU: PCSD623
Price: 20 EUR
Availability: InStock

20 €VAT includedIn stock · 5 units

Pressure switch: refurbished spare part that controls air or water pressure to authorize operation. Useful if the boiler does not start or shows a draft error. Reference 05156000. Includes a one-year warranty and delivery within 2–4 working days in the EU.

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Delivery in 2–4 working days

1-year warranty

14-day return

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Key Data

Reference: 05156000
Brand: Saunier Duval
Type of part: Pressure switches
Available units: 5 units in stock
Status: Refurbished
Warranty: 1 year
Shipping: 2–4 working days (EU)
Return: 14 days

Fault codes related to this part (not the entire boiler). They usually have more possible causes: first rule out electrodes, wiring/connections, and gas supply. Verified with ≥3 sources.

Code	What does it mean?	Cause and diagnosis (this part)
F2	Safety Flue Test (SFT) / air pressure switch fault.	If the pressure switch does not switch on start-up, the PCB detects a lack of flue depression and locks out with SFT. Check silicone tubes/Venturi and the switching by applying controlled depression and measuring continuity at the contacts.
F33	Airflow fault due to open/defective air pressure switch.	The pressure switch contact remains open or stuck, preventing the draft validation. Check with a vacuum pump/manometer and multimeter the triggering pressure and the closing/opening; inspect the venturi, flue duct, and fan to rule out obstructions.