While you wait for answers, we may have found some information which could help you.
Click here for Manual Engineers CodesSaunier Duval timeclock not working?
How can I fix my Saunier Duval Semia Condens boiler?
Saunier Duval Isofast condens F35E....nothing working?
'f19' error report - Saunier Duval 'Thermoclassic' boiler?
How to repair F4 code?
isotwin condens f 35 e service menu codes?