Diagnose a Sump Pump That Won't Turn On
Category: Plumbing ·
Difficulty: Intermediate ·
Time: 1.8h ·
Estimated cost: $55
Tools needed
- GFCI outlet tester
- Voltage tester pen
- Multimeter
- Bucket
- Garden hose
- Channel-lock pliers
- Flashlight
Materials needed
- Replacement float switch (1 ea)
- Replacement GFCI outlet (if needed) (1 ea)
- Plumbers tape (1 roll)
Execution steps
Test the outlet
Unplug pump. Plug the GFCI tester into the outlet. If it shows fault or no power, that's your problem — reset the GFCI or replace the outlet.
Duration: 10 min
Test the pump direct
Plug the pump straight into a known-good extension cord. If it runs, the original outlet is bad. If silent, the pump or float is the problem.
Duration: 10 min
Check the float
Lift the float manually with a stick. Pump should kick on instantly. If it doesn't, the float switch is dead.
Duration: 10 min
Pour test
Pour 5 gallons of water into the pit. Float should rise and trigger the pump. If float rises but no pump action, replace the float switch.
Duration: 15 min
Swap float switch
Unplug pump. Disconnect old float per its clamp or wire connector. Install replacement, clip to the discharge pipe at the manufacturer-spec height.
Duration: 45 min
Verify discharge clear
Check that the outdoor discharge line is not blocked by ice, dirt, or a stuck check valve. Pour another 5 gallons and watch a full pump cycle.
Duration: 15 min
Safety first
- ALWAYS unplug the pump before reaching into the pit — water + electricity = death.
- If the basement has standing water, do NOT step into it until power to the pump and basement outlets is OFF at the breaker.
When to hire a pro
If the pump runs but doesn't move water, the impeller is shot — easier to swap the whole pump. If the pit fills faster than any pump can keep up, hire a waterproofing contractor.
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