I have a Riello 40 and for some reason it doesn't hold its prime, I have to bleed it at lease once and even twice a day in order for it to keep it running.
air is getting into you line somewhere, check all the connections in your flexable oil lines are tight as well as the bleeding screw on the pump (the one marked V) if you hold your finger over a water filled hosepipe the water dosn``t run out, if a little air gets in the water runs out, these are the easiest thing to check first hope it helps
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