Leak only when shower on long

Quick Answer:

If the tub spout only leaks after the shower has been running for a while, note exactly when the leak starts. That timing often points to heat and thermal expansion affecting seals or the diverter. Try lowering the water heater a few degrees (aim for about 120°F / 49°C), retest, and if the leak keeps returning after the water warms, call a plumber.

Why This Happens

Long showers let fixtures reach higher temperatures. Metal parts and rubber seals expand at different rates when heated. Small gaps that are closed when cold can open as parts expand, or older O-rings and seals can soften and shift. If the leak reliably appears after several minutes of hot water, thermal expansion or heat-softened seals are common causes.

If the problem began after work on the bathroom, check notes and parts used — a recent change can introduce a fit or seal issue. See Leak started after remodel for related troubleshooting steps you might recognize.

Step-by-Step What to Do

1. Observe and time it

• Run a long shower as you normally would and use a clock or phone to note the minute the leak first appears.
• Record whether the leak starts when water first turns hot, after a specific number of minutes, or only at very high temperature settings.

2. Look for obvious, simple fixes

• When the leak is visible, check for loose fittings around the tub spout and nearby trim. Tighten only by hand or with a soft cloth—don’t force metal parts.
• Wipe the area dry, run the shower again, and watch for where water is coming from (spout, joint, or the diverter slot).

3. Test for heat-related causes by adjusting water temperature

• Reduce the water heater setting slightly (a safe target is about 120°F / 49°C). Lower it by 5–10°F from the current setting if you can, then let the heater stabilize and retest with a long shower.
• If the leak stops or is delayed, heat-related expansion or softened seals are likely contributors.

4. Try a temporary small adjustment if comfortable

• If you find a loose escutcheon or trim nut and you are comfortable doing minor tightening, do so gently. If you’re not certain, skip this and contact a professional.
• If the tub spout drips only after the shower warms up, compare how it behaves with cold-only flow and with longer hot flow to confirm the pattern.

5. Monitor and document

• Keep a short log over a few days: start time, how long before the leak, water temp setting, and any visible changes. This helps a plumber diagnose the issue faster if you call one.

What Not to Do

• Don’t ignore leaks that start late in the shower—heat-related expansion can worsen and lead to bigger failures or water damage.
• Don’t force parts or use excessive tools on chrome trim and visible fittings; you can strip threads or crack fixtures.
• Don’t apply permanent sealants or adhesives as a quick fix without understanding the source; that can hide the real problem and make future repairs harder.
• Don’t delay calling a pro if the leak becomes consistent even after testing temperature changes—ongoing leaks need proper repair.

When to Call a Professional

• If the leak continues to start reliably after the water warms even after you lower the heater temperature.
• If you see water damage, staining, mold, or moisture where it can affect walls or flooring.
• If you are not comfortable making simple checks or tightening visible parts, or if the leak source is inside the wall or from the diverter.

Safety Notes

• Be cautious of scalding. Let hot water cool before placing your hands under a stream to inspect the spout.
• If you adjust the water heater, follow the manufacturer’s instructions or have someone familiar with your heater do it. A safe household setpoint is around 120°F (49°C).
• If you must shut off water to try something, use the local shutoff valves if you know their location and function. If unsure, call a professional to avoid causing more damage.

Common Homeowner Questions

• Will lowering the heater fix it? Often it will reduce or delay a heat-related leak, but it may not fix worn seals or mechanical faults.
• Can I replace the spout or diverter myself? If you have basic plumbing experience and the spout is a simple slip-on or screw type, possibly—but stop and call a pro if the work requires opening the wall or altering piping.
• Is the problem urgent? If the leak only appears after a long shower and is small, monitor it; if it becomes consistent, larger, or causes damage, get a plumber promptly.

For related issues you notice after work in the bathroom, and for tips about a spout that drips after you stop a shower, see Tub spout drips after shower.