Before priming, the wall surface should be cleaned aggressively with a scrub brush. We have used Scrubbing Bubbles, Krud Kutter, etc. The final cleaning is with TSP. (My DW even resorted to using a steamer.)
EDIT: In our Boler
13, we actually prepped and painted as described above. In our Trillium
4500, we cleaned and steamed, but did not paint as the ensolite was/is in great condition.