While you wait for answers, we may have found some information which could help you.
Click here for Saunier Duval Hotsaunier duval boiler problem?
saunier Duval is over pressurising when the heating is on. ?
isotwin condens f 35 e service menu codes?
How to repair F4 code?
Saunier Duval Isofast condens F35E....nothing working?
Saunier Duval F35E auto-vents down to code 21 in minutes?