While you wait for answers, we may have found some information which could help you.
Click here for Increasing Water Pressuresaunier Duval is over pressurising when the heating is on. ?
'f19' error report - Saunier Duval 'Thermoclassic' boiler?
How to repair F4 code?
Saunier Duval Isofast condens F35E....nothing working?
Saunier Duval timeclock not working?
I have a Saunier Duval Isotwin condens F 35 E with hot water No heating?