We are finding that more of our customers have been letting their submersible pumps run dry. This is a serious problem because these pumps must have water running through them at ALL times. If the fountain bowl runs out of water the pump will burn out rapidly. It is recommended, when possible, to install a fountain float valve kit to keep water in your fountain replenished so it doesn't run dry. It does not take long at all for a submersible pump to burn out these days if no water is going through it.
Part of the problem is that there is a misunderstanding about how most fountain pumps now operate. Most fountain pumps are now magnetic drive. They are not like the older pumps with copper windings. Magnets provide the power for the flow. We hear from customers that "bearings are shot" or that "something is wrong with the armature." If by armature, you mean the magnetic impeller and shaft, it could be that the impeller is indeed shot. But usually these impellers do not go bad unless they run without water or in a clogged state. Please note that there are magnets in most fountain pumps nowadays. Some customers plug in their pumps out of water "for testing" and report loud noises. That is because no water is going through the pumps.
Though some pumps have sensors in them that will shut off the pump when it runs dry, too much shutting off can wear out the sensor so the pump will never start, so we have decided not to include a sensor shutoff option in our pumps.
We recommend that no one "test" their fountain pumps out of water.
If you have a Scott or Kasco fountain pump, then these are built differently. However, they still must NOT ever be run out of water.