Quick Answer:
If a leak shows up mainly when you run hot water, temperature-driven expansion or softening of seals is often the cause. Check the exact leak location while alternating cold and hot water to confirm whether heat opens a marginal seal. Small leaks can look minor at first but often get worse, so test and address the source promptly.
Why This Happens
Hot water changes the size and flexibility of pipes, gaskets and seals. Rubber or plastic parts can swell, soften or shift when warm, opening a tiny gap that stays closed with cold water. Metal parts expand slightly and can loosen around threaded fittings or warped flanges. A marginal seal that seals with cold water may leak when it warms and moves even a little.
Step-by-Step What to Do
1. Prepare for a simple test
- Place a shallow tray or towels under the disposal and drain connections to catch water.
- Have a flashlight and a helper if possible so one person runs water while the other watches.
2. Test cold versus hot water
- Run cold water at normal flow for 30–60 seconds while watching the disposal, mounting area, tailpipe, dishwasher inlet and trap for leaks.
- Run hot water for the same time and watch the same spots. Note exactly where water appears first and whether drips increase with heat.
- Repeat the test a couple of times to be sure the pattern is consistent.
3. Identify common leak points
- Sink flange and disposer mounting ring where the unit meets the sink.
- Discharge tailpipe and slip joint to the drain trap.
- Dishwasher inlet connection where the dishwasher drain hose meets the disposer.
- Body or seams of the disposal if the housing is cracked or corroded.
4. Do basic fixes you can do safely
- Tighten loose slip nuts by hand and then a quarter turn with a wrench—do not overtighten.
- Replace worn compression washers or slip-joint washers if visible and accessible.
- Hand-tighten the dishwasher hose clamp or nut; replace a split hose or clamp if needed.
- After any change, repeat the cold/hot test to confirm the leak is fixed.
5. When a specific source needs more attention
- If water appears where the dishwasher hose meets the disposer, check the hose and clamp or consult the **Disposal leaks at dishwasher inlet** resource.
- If the leak started or changed after you worked on the mounting flange or tightened the unit, check the mounting ring and read the **Leak after tightening mounting ring** guidance.
What Not to Do
- Do not assume hot-water-only leaks will go away; expansion-related leaks often worsen over time.
- Do not put your hand into the disposal or try repairs while it has power. Always switch the unit off and disconnect power at the breaker before reaching inside.
- Do not overtighten metal fittings or mounting screws—this can crack seals or damage the sink flange.
When to Call a Professional
Call a plumber if:
- The leak continues after basic tightening and gasket replacement.
- Water appears from the disposal body (possible internal crack or failed seam).
- The mounting assembly seems loose, warped, or leaking at the sink flange and you’re not comfortable removing the unit.
- There is any electrical sparking, moisture near wiring, or you cannot safely isolate power to the disposal.
Safety Notes
- Turn off the disposal and cut power at the breaker before working on or under the sink.
- Never use your hand to probe the disposer chamber; use a flashlight and tools from the outside.
- Wear eye protection and gloves when handling old gaskets or corroded metal parts.
- Work with a helper when possible so someone can run water while you watch without reaching into the unit.
Common Homeowner Questions
- Why does it leak only with hot water? Hot water can soften seals or expand metal parts, opening a small gap that lets water escape.
- Can I fix it myself? Often you can tighten fittings, replace a washer or hose clamp; stop and call a plumber if the source is the disposer body or mounting flange.
- Will replacing the disposal solve it? If the body or internal seals are failing, replacing the unit will fix it; if the leak is at a connection, replacement may not be necessary.