Noisy Saunier Duval Thelia 20 n No Hot Water / Heating but pilot ON?

from your description it seems to be stuck in some sort of pump overrun mode
i.e. pilot lit main burner off fan & pump running
there could be several reasons for the boiler doing this

i would check the overheat stat first
it might be possible to manually reset it
then i would check the resistance on the NTC thermistors
if these test ok you are now looking at the more expensive components
if you dont know how to test these components then youll have to call in an expert

AWOL
June 2012