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Garbage disposal repair, and what the unit sends downstream
We look at the unit and the line it empties into as one question, not two, because a disposal running perfectly into a failing cast iron drain is not actually a success.
It hums but the disposal will not spin. Is that the end of it?
Not necessarily. A hum tells you the motor has power, and something is blocking the plate from rotating. That is a jam, not a burnout. Underneath most units sits a reset button and a hex socket that frees the plate by hand. If there is no hum at all, the cause shifts: power supply, the wall switch, or a motor that has quit.
The more useful question in this climate is what sits downstream of the unit. A South Florida home built before roughly 1975 almost always drains through cast iron, and decades of scale have already roughened that pipe’s interior. Ground-up scraps, along with whatever grease travels with them, are exactly what a rough interior wall grabs and holds.
On an older line, the disposal is no longer a harmless convenience under the counter. It piles extra demand onto the pipe with the least capacity left to handle it, worth knowing before swapping in a new unit and hoping the drain problem disappears.
What you are seeing
What each symptom means, before assuming the worst
Two of these are about the unit. Three are not.
It hums, but the plate will not spin
Jammed, most likely. The reset button and the hex fitting underneath free the plate on most units, and the disposal is generally none the worse for it afterward.
Complete silence when the switch is flipped
Power, the switch, or the motor itself. The reset button is still worth pressing first, since it trips on overload and stays tripped until someone resets it.
Water appears under the sink while it runs
Look first at the sink flange, the discharge tube, or the dishwasher hose connection. A joint has likely started weeping. A cracked housing is possible but far less common than a fitting that simply needs resealing.
The sink backs up whenever it is used
The pipe downstream has lost capacity, not the unit. No disposal, however powerful, can force waste through a drain that no longer has the diameter to carry it.
It has grown noticeably louder over time
Worn bearings, or something that has been sitting in there a while. Either is worth a look before the motor makes the decision for you.
Questions
Straight answers before you call
Does a disposal make sense in an older house at all?
It deserves a real answer rather than a reflexive yes. Cast iron that has already scaled down grabs ground waste and grease before either gets very far, so adding a disposal piles more work onto the weakest link in the system. Better to hear that up front than to install one and get a call from you about the drain a season later.
What should genuinely never go down a disposal?
Grease first and worst, since it lines the pipe instead of moving through it. Bones, fibrous vegetable trimmings and coffee grounds cause their own headaches, but grease specifically is what turns into a repeat drain-cleaning bill in a region like this one.
Can a jammed disposal be freed without calling anyone?
Frequently, yes. Kill the power at the switch, press the reset button underneath, and work the hex key into the base to rock the plate loose by hand. If that clears it and the unit runs normally afterward, there is no call to make.
Is a failing disposal usually repaired, or replaced?
A jam or a leaking fitting is a repair, plain and simple. A burned-out motor or worn bearings point toward replacement instead, since the unit is built as a sealed appliance rather than something meant to be rebuilt piece by piece. Either way, you get a direct answer rather than a guess.
Related work
Nearby jobs a disposal call can turn into
Three of the five symptoms above end up being about the drain rather than the disposal.
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Humming, leaking under the sink, or backing up?
Someone answers the phone at any hour. When the sink is backing up rather than the disposal failing, that is exactly what gets said, not a pitch for a new unit.
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