While you wait for answers, we may have found some information which could help you.
Click here for Saunier Duval Boiler Problemsaunier duval boiler problem?
saunier Duval is over pressurising when the heating is on. ?
Saunier Duval F35E auto-vents down to code 21 in minutes?
How to repair F4 code?
'f19' error report - Saunier Duval 'Thermoclassic' boiler?
Saunier Duval Thema F23 anyone have a link for manual?