While you wait for answers, we may have found some information which could help you.
Click here for Saunier Duval HotSaunier Duval timeclock not working?
saunier Duval is over pressurising when the heating is on. ?
Saunier Duval Isofast condens F35E....nothing working?
Saunier Duval F35E auto-vents down to code 21 in minutes?
saunier duval sd620f?
How to repair F4 code?