Quick Answer:
If a shower starts dripping only after long, hot showers, the most likely causes are thermal expansion or heat-related behavior of the valve seal or cartridge. Run a short cool shower and a long hot shower to confirm. If the drip appears only after long hot runs, lower the water heater temperature a few degrees (aim near 120°F) and retest; if the pattern repeats, contact a plumber.
Why This Happens
Long hot showers heat the plumbing and the valve assembly more than short showers do. Metal and rubber parts expand with heat; seals and cartridges can change shape or seating under sustained high temperature. That slight change can allow a slow drip that only appears after extended hot use. Mineral buildup and worn seals make the effect more likely over time.
You can compare this scenario to other heat-related patterns, such as Shower drips when water heater runs, and it behaves differently than pressure-based leaks you might see after an event like a water outage, similar to Dripping after city outage.
Step-by-Step What to Do
1. Reproduce the problem
- Run a short (1–2 minute) hot shower and check the showerhead and valve for dripping after you turn it off.
- Next, run a long (10–15 minute) hot shower at the same faucet and check again immediately after shutting it off and 5–10 minutes later.
- Note whether the drip appears only after the long run.
2. Compare short vs long results
- If the shower only drips after the long run, that points toward thermal expansion or seal behavior rather than a constant leak from damage or loose fittings.
- If it drips after both short and long runs, the problem is likely a worn cartridge, seat, or loose connection and needs more direct repair.
3. Reduce water heater temperature slightly and retest
- Lower your water heater temperature by 5–10°F (for example from 130°F to 120–125°F) and wait for the heater to settle (30–60 minutes for tank heaters).
- Repeat the short/long shower test to see if the long-only drip stops or is reduced.
- If lowering the temperature stops the drip, thermal expansion or heat-softened seals were likely the cause.
4. Monitor and document
- Keep a short log: date, heater setting, shower length, and whether a drip appeared. This helps a plumber diagnose the issue if it recurs.
- If reducing temperature helps but the drip returns over weeks, it suggests a part is wearing and may need replacement.
What Not to Do
- Don’t treat long-shower-only dripping by raising heater temperature—this can worsen expansion.
- Don’t try to fix internal cartridge or valve parts while the water heater or water supply is still hot and pressurized; that’s a burn and injury risk.
- If the drip is repeatable after your tests and adjustments, a plumber is appropriate to inspect and, if needed, replace the valve or cartridge rather than relying on temperature changes alone.
When to Call a Professional
- Call a plumber if the drip continues after you reduce the water temperature and perform the short/long test.
- Also call if the drip worsens, if you see leaks elsewhere, or if you notice reduced hot water flow or fluctuating pressure—these can indicate a failing mixing valve, cartridge, or corrosion that needs professional repair.
- A licensed plumber can test thermal expansion, check the mixing valve or cartridge, and replace worn parts safely.
Safety Notes
- Aim for a water heater temperature around 120°F (49°C). This is a common, safe balance between reducing scald risk and maintaining hot water for household use.
- Lower the heater in small steps (5°F) and retest. Avoid setting temperatures well below 120°F without understanding the effects on bacteria growth or household needs.
- Turn off power or gas to the water heater before attempting any internal repairs or when a professional advises it. Do not disassemble gas or electric heaters yourself unless you are qualified.
Common Homeowner Questions
- Why did this start only after long showers? Heat from a long run causes parts to expand or seals to soften, revealing a small leak that doesn’t show after short showers.
- Will lowering the heater temperature always fix it? Not always—lowering temperature can stop heat-related leaks, but worn parts may still need replacement.
- Is this dangerous to leave alone? A slow drip after showers is usually not an emergency, but it can waste water and indicate a part that will fail; have a plumber check persistent or worsening leaks.
For more related articles, see the Dripping Showerhead After Shutoff hub.