I installed geo-thermal heating/cooling in my home when I built it in the late 80's. There 6 pumps involved. The testers are cute, but I have always wondered about them. I know I should get one but I just use my hand to know if the pump is running.

What I am wondering is, does the tester spin when the armature in the motor spins, OR will it spin even if motor it energized as the magnetic fields would be moving even though the armature could be stuck. Most of those type pumps are impedance protected, and will not burn up even if the armature is stalled.

Has anyone used one?