Hi @mattlang,
Sounds like the pump is not primed.
Has the pump worked OK before in the same setup?
Here’s the [https://items.marco.it/media//attach/booklet/UP6-A_00_ENG.PDF|user manual] for the pump.
Go to p.12 to see the troubleshooting reasons why the pump may not be primed.
On p.14 there is a parts diagram and here’s the [[Topic:Marco UP Series Electric Pump]] guides that may also help.