What is the most common reason a sump pump fails?

Answer: Switch malfunction
Explanation: I would say the most common issue with sump pumps would be the float switch that tells the pump to turn on when the water reaches a predetermined level and aslo tells the pump when to turn off. Typically an easy fix with ample access to the pump.

Answer: Switch malfunction
Explanation: Switch failure is the number one cause of pump malfunction because of constant wear and tear. They do offer pumps with none moving floats that will last much longer.

Answer: Power failure
Explanation: When power cuts out its very common