The answer to 'sump pump not working' is that the most common causes are a tripped circuit breaker, a faulty sump pump motor, a clogged or frozen discharge line, or a problem with the sump pump float switch. Symptoms may include the sump pump not turning on, running continuously, or failing to pump water effectively.
To troubleshoot, first check the circuit breaker and reset it if tripped. Next, inspect the sump pump itself - listen for the motor running and check that the float switch is moving freely. If the pump is not running, the motor may need to be replaced. If the pump is running but not pumping, the discharge line may be clogged or frozen, requiring cleaning or thawing. If the float switch is stuck, you may be able to free it, but if the switch is faulty, it will need to be replaced.