There is also a switch on the pump that senses a drop in pressure which turns on the pump.
Especially with a new rig, this switch could become clogged with residue from the manufacturing process of the water lines. This happened with a boat I owned. After a period of time, some kind of "slime" got into the water pump that had to be cleaned out. Boats have very similar plumbing systems to RVs, and often use the same components.
All I can imagine as to the source of the slime was something left over from constructing the boat, as well as the marina dealer telling me that post-construction debris fouling the pump was a common issue with new boats.
The only thing that works on a RV is the owner...