While you wait for answers, we may have found some information which could help you.
Click here for Saunier Duval Tapsaunier duval boiler problem?
Saunier Duval timeclock not working?
isotwin condens f 35 e service menu codes?
'f19' error report - Saunier Duval 'Thermoclassic' boiler?
Saunier Duval F35E auto-vents down to code 21 in minutes?
I have a Saunier Duval Isotwin condens F 35 E with hot water No heating?