First I would try tipping the pump upside down in the reservoir, they can get an airlock and the air needs to be purged for the pump to prime.
If this does not solve the problem I would try to verify the pump is indeed the issue by touching the pump wires to the terminals of a 9V battery, if it does not run or runs but you can see the impeller in the bottom opening is not spinning, then we know the pump is the issue.
From their if you can email me your invoice and a photo of the pump showing the impeller through the opening, we can get it replaced. Tunze at sbcglobal dot net