Quick Answer:
If the disposal only hums after you installed a new switch, the most likely causes are a wiring mistake, a loose connection, or a jammed rotor that is getting power but not turning. Start by cutting power at the breaker, then confirm the wiring at the switch and under-sink connection matches the disposal’s requirements and check for loose wires. If wiring looks correct and the unit still hums, the motor may be stalled or failing and you should call a professional.
Why This Happens
- Humming usually means the motor is getting some power but cannot spin. That can be from a mechanical jam or from poor/incorrect electrical connections delivering reduced or intermittent power.
- If wires at the new switch were swapped (for example a neutral and hot), the disposal may get power in an unexpected way and only hum without turning.
- Loose wire nuts or a loose terminal under the sink can drop voltage under load, causing the motor to struggle and hum.
- If you recently changed a switch that also controls the dishwasher or was part of a shared circuit, note interactions like a dishwasher causing the disposal to stop; see **Disposal stops when dishwasher runs** for related troubleshooting ideas.
Step-by-Step What to Do
1. Turn off power at the breaker
- Locate the circuit breaker that controls the kitchen or disposal and switch it off. Do not rely on the wall switch alone.
- Confirm the power is off by trying the switch or using a non-contact voltage tester if you have one and know how to use it safely.
2. Inspect the switch wiring
- Remove the switch cover and check that the incoming hot (power) is connected to the common or line terminal and the switched hot goes to the disposal circuit. Confirm the wiring at the switch and under-sink connection matches the disposal’s requirements.
- Look for loose screws or wire nuts and tighten them. If wires look frayed, trim back and re-strip a little before reconnecting.
- If the switch is a new style (e.g., a smart switch or dimmer-style device), make sure it is compatible with a garbage disposal and wired according to the device instructions.
3. Check the under-sink connections
- Open the disposal access area. Inspect the connections on the disposal’s wiring block: neutrals should be properly tied, and the switched hot should be connected where the disposal expects it.
- Ensure all wire nuts are tight and conductors are fully inserted. Check for any signs of overheating or burnt insulation.
- Gently tug each wire to confirm it’s secure.
4. Try the reset and check for jams
- With power still off, use a wooden spoon handle or the manufacturer’s wrench (if provided) to rotate the impeller from below to free a possible jam—never use your fingers.
- Press the disposal’s reset button (usually red and on the bottom). Then restore power at the breaker and try the switch briefly while running cold water.
5. Test operation safely
- Turn the breaker back on and have a partner flip the switch while you stand clear. If it hums again, turn power off and re-check wiring and connections.
- If the unit runs briefly and then trips the reset or breaker, that suggests either an electrical fault or a motor problem.
6. Next steps if humming persists
- If wiring and connections are correct and the disposal still hums, the motor may be seized or failing. At this point, it’s safer to contact a qualified technician.
- For issues where blades won’t rotate but you suspect the motor is fine, troubleshooting guides like **Disposal blades won’t rotate** explain common mechanical causes and safe checks.
What Not to Do
- Do not wire a new switch without verifying connections—if you’re unsure, an electrician is appropriate.
- Do not put your hand into the disposal while power is on or before you are certain the power is off.
- Do not use excessive force on electrical terminals; tightening should be firm but careful to avoid breaking screws or wires.
- Do not bypass a switch or reset circuit protection to get the unit running; that can create a fire or shock hazard.
When to Call a Professional
- Wiring is confusing or you can’t confirm correct connections — call a licensed electrician.
- The disposal still hums after you’ve confirmed wiring and cleared any jam — suspect a failed motor or internal electrical fault and call a plumber or appliance technician.
- Any signs of burning, smoke, melted insulation, or tripping breakers repeatedly — stop and call a professional immediately.
Safety Notes
- Always switch the breaker off before working on a switch or disposal. Confirm power is off with a tester if possible.
- Use tools, not hands, to clear jams. Never reach into the disposal while it has power available.
- If you are uncomfortable working with wiring or unsure about the circuit, hire an electrician. Electrical mistakes can cause shock or fire.
Common Homeowner Questions
- Why does the disposal hum but not run? — It usually means the motor is powered but cannot rotate due to a jam, poor power delivery from a loose connection, or a failing motor.
- Can I test voltage at the switch myself? — Only if you have the right tester and experience; otherwise hire an electrician to avoid risk.
- How long before I should replace the disposal? — If the motor fails or the unit trips often after correct wiring and clearing jams, replacement is often more cost-effective than repair.