While you wait for answers, we may have found some information which could help you.
Click here for Saunier Duval Heating PressureSaunier Duval F35E auto-vents down to code 21 in minutes?
How can I fix my Saunier Duval Semia Condens boiler?
How to repair F4 code?
Saunier Duval Isofast condens F35E....nothing working?
Saunier Duval timeclock not working?
saunier Duval is over pressurising when the heating is on. ?