Sump Pump Not Working: Causes & How to Fix It
A non-working sump pump often stems from power loss, a stuck float switch, clogged discharge pipes, or a failed check valve—most of which you can diagnose in under an hour. Replacing a sump pump motor or the entire unit costs between 300 and 800 dollars, but many issues are fixable for under 50 dollars in parts. This guide walks you through testing power, clearing blockages, and identifying when the pump itself has failed.
Step-by-Step Fix
- 1
Check power and GFCI outlet
Verify the sump pump is plugged in and the outlet has power by plugging in a lamp or phone charger. If the outlet is dead, reset the GFCI breaker (the outlet may have a reset button, or check your electrical panel). Test the pump again after power is restored.
- 2
Inspect the float switch
Lift the pump cover and look at the float ball or arm—it should move freely up and down without obstruction. If it's stuck or resting on the pump housing, gently reposition it so it can rise with water level. A stuck float prevents the pump from turning on even when water is present.
- 3
Clear the discharge pipe
Follow the pipe leaving the sump pit to where it exits your basement or crawlspace. Remove any visible debris, ice, or sediment blocking the opening. If the pipe is frozen in winter, pour warm (not boiling) water over it or use a heat gun to thaw it, then test the pump by pouring water into the pit.
- 4
Test the check valve
Locate the one-way check valve in the discharge line (usually a flapper or ball valve near the pump outlet). Open it by hand to ensure it moves freely and isn't jammed with debris. A stuck check valve traps water in the line and prevents the pump from draining, making it sound like the pump has failed.
- 5
Listen and feel for pump operation
Pour water into the sump pit to trigger the float switch. You should hear the pump motor hum and feel vibration within 10 seconds. If there's no sound or movement, the motor has likely failed and the pump needs replacement. If the pump runs but water doesn't drain, the discharge line is blocked further downstream.
- 6
Replace the pump if it won't start
If power, float, and discharge are all clear but the pump still doesn't run, the motor or impeller has failed. Turn off power, unplug the pump, and unbolt it from the sump basin. Install a new pump by reversing the steps, ensuring the discharge line is firmly connected and the float switch hangs freely.
⚠️ Safety Notes
- Never touch the pump or water in the pit while it is plugged in; always disconnect power before opening or servicing any pump component.
- Do not pour boiling water on a frozen discharge pipe—rapid temperature changes can crack PVC. Use warm water or a heat gun instead.
- Sump water may contain sewage backup or contamination in some systems; wear gloves and wash your hands thoroughly after handling pit water or components.
When to Call a Pro
Call a plumber if the pump motor will not run despite confirmed power, a free-moving float, and a clear discharge line, or if water is backing up into your basement and the pump has already been replaced. A professional can diagnose electrical faults, check for a failed impeller, or identify a system design problem.
Frequently Asked Questions
- Why did my sump pump suddenly stop working?
- The most common causes are a power loss to the outlet, a stuck float switch, or a clogged discharge line. Check that the outlet has power, the float moves freely, and the pipe exiting your home isn't blocked by ice or sediment.
- How do I know if my sump pump motor is dead?
- If power is on, the float switch is free to move, and the discharge pipe is clear but the pump still doesn't hum or vibrate when water enters the pit, the motor has failed and the pump needs replacement.
- Can I fix a frozen sump pump discharge pipe myself?
- Yes; use warm (not boiling) water or a heat gun to thaw the frozen section, starting from the end closest to the house and working outward. Once thawed, test the pump by pouring water into the pit.
- What does a check valve do, and can it cause pump failure?
- A check valve allows water to flow out but prevents it from flowing back into the pit. If it gets stuck closed, the pump runs but water won't drain, making it seem like the pump has failed. Free it by hand or replace it if it's damaged.
- How much does it cost to replace a sump pump?
- A new sump pump costs between 300 and 800 dollars installed, depending on motor size and pump type. Many common failures like float switches or check valves cost under 50 dollars and take 20-30 minutes to fix yourself.
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