Could be...Loss of suction...air entry...insufficient flow rate in feed
pipe. Can you watch it get lower?

Is your pump a gravity-flooded prime or does it need to suck water up
to the pump. If it can draw from a flooded reservoir, it is less
likely to pull itself dry. To do that, the pump needs to be lower than
the pond level and has to have sufficient flow to keep drawing water
instead of air.

Jim


Bob wrote:
I recently installed an external pump with a priming pot for my pond.
After a few hours of running I discover that the pump is still running
but there is no water flow and the priming pot is empty of water. I
can stop the pump, refill the priming pot, restart it and it will pump
water for a few more hours until it runs out again. I am confident
that the power to the pump has not gone out temporarily. I have also
verified that I can remove power from the pump and restart it just
fine, since I have a swing valve on the input of the priming pot that
prevents it from emptying. Any ideas as to what could be causing this?