Vaillant HOME SYSTEM 12 -A Operating Instructions Manual page 16

Appendix
Fault
Product does not After three successive failed ignition
start up: attempts, the system switches to fault
mode (fault code: F.28).
– No hot water
– Heating does
not heat up
Hot water gener- The external controller is not set cor-
ation functioning rectly.
correctly; heating
does not start up.
16
Cause
Operating instructions HOME 0020224356_00
Measure
Press the button. The product
carries out a new ignition attempt.
If the ignition problem is not rec-
tified after three fault clearance
attempts, contact a competent
person.
Set the external controller cor-
rectly (→ Controller operating in-
structions).