We may have found other answers which could help you.
Click here for Saunier Duval HotI have a Saunier Duval Isotwin condens F 35 E with hot water No heating?
How to repair F4 code?
Saunier D’uval therma classuc?
Saunier Duval Isofast condens F35E....nothing working?
Saunier Duval F35E auto-vents down to code 21 in minutes?
saunier duval boiler problem?