Finding pin holes in a closed loop system

[my2rotties]

The sump is full. The water gets sucked into the return pump from the bottom of the sump not the top. The water would have to be drained right out for it to be sucking air. I feel that the pump is cavitating and on it's way, out but the LFS INSISTS there is a pin hole in my system. I don't know much abut how the system works but I cannot see how it is possible to have a pin hole to be honest. Sorry about my lack of knowledge on the set up. I watched it get built but do not know the technical names of all of it. I just take care fo the entire system except for broken things.

Originally Posted by Mr OM

Then it isn't a closed loop but a standard return.
It could be a number of things, but based on the fact that hubby is out playing hockey I would think that your sump may be running dry and air is being sucked in.