While you wait for answers, we may have found some information which could help you.
Click here for Water Luke WarmHow to repair F4 code?
saunier Duval is over pressurising when the heating is on. ?
isotwin condens f 35 e service menu codes?
Saunier Duval Isofast condens F35E....nothing working?
Saunier Duval F35E auto-vents down to code 21 in minutes?
Saunier Duval timeclock not working?