While you wait for answers, we may have found some information which could help you.
Click here for Saunier Duval Boiler WaterHow to repair F4 code?
'f19' error report - Saunier Duval 'Thermoclassic' boiler?
saunier duval sd620f?
Saunier Duval Thema F23 anyone have a link for manual?
Saunier Duval timeclock not working?
How can I fix my Saunier Duval Semia Condens boiler?