While you wait for answers, we may have found some information which could help you.
Click here for Heat Hot Water Light BoilerSaunier Duval F35E auto-vents down to code 21 in minutes?
saunier duval sd620f?
How to repair F4 code?
saunier duval boiler problem?
isotwin condens f 35 e service menu codes?
Saunier Duval Thema F23 anyone have a link for manual?