While you wait for answers, we may have found some information which could help you.
Click here for Boiler Noticed Low WaterSaunier Duval Isofast condens F35E....nothing working?
saunier duval boiler problem?
Saunier Duval timeclock not working?
'f19' error report - Saunier Duval 'Thermoclassic' boiler?
How to repair F4 code?
Saunier Duval Thema F23 anyone have a link for manual?