Check that there is coolant in the tank to begin with !
Sounds silly ? not so, been there, done that !
If the tank is full, check that there are no valves closed and that the pump is running the right way [simple things mean a lot ! ] These pumps are usually trouble free, so it has to be something simple
As an aside, the pump fitted to the cooling system on my bandsaw, came from a clapped out washing machine. Still working after ten years or more.
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