Installing a shower/tub combo is exciting—but skipping a critical step could lead to expensive water damage hidden behind your beautiful new surround. Many DIYers and even some contractors rush through the process, only to discover leaks after the walls are sealed. Checking combo shower/tub plumbing for leaks before putting surround up isn’t just smart—it’s essential. In this guide, you’ll learn exactly how to do it right, safely and confidently, even if you’ve never touched a pipe before.
Why Should You Test Plumbing Before Installing the Surround?
Water leaks behind bathroom walls are a silent disaster. According to the Insurance Institute for Business & Home Safety, plumbing leaks account for nearly 50% of all homeowner insurance claims related to water damage—and the average repair costs $5,000+.
Once your tile or acrylic surround is up, accessing pipes means tearing down walls, risking mold, structural damage, and ruined finishes. Testing before you seal everything in saves you hundreds (or thousands) of dollars and weeks of remediation.
“Never assume new plumbing is leak-free. Even factory-tested valves can fail when installed under pressure or misaligned,” says Mike Johnson, a licensed master plumber with 22 years of experience in residential remodels.
What Does “Combo Shower/Tub Plumbing” Include?
A combo unit typically shares:
- One drain (with a diverter to switch between tub fill and shower flow)
- Hot and cold supply lines feeding both the tub spout and showerhead
- A mixing valve or pressure-balancing valve behind the wall
- Overflow pipe connected to the tub
- Shower arm and flange penetrating the wall
All these components must be pressure-tested before any wall covering goes up.
Step-by-Step: How to Check for Leaks Before Installing Your Surround
Follow this proven 6-step method—used by pros and endorsed by building codes like the IPC (International Plumbing Code).
Step 1: Cap All Openings
Close the system by capping or plugging:
- Shower arm outlet
- Tub spout outlet
- Drain opening (use a test plug or inflatable drain seal)
⚠️ Tip: Use 2-inch rubber test plugs for standard drains. Inflate to 8–10 PSI—enough to seal, not burst.
Step 2: Pressurize the System
Connect your water supply and turn on both hot and cold lines. Let water run for 30 seconds to flush air, then shut off.
Now, isolate the system by closing angle stops or using a pressure test gauge (available for ~$25 at hardware stores).
- Ideal test pressure: 60–80 PSI (standard household pressure)
- Hold for at least 15 minutes—30 is better
🔍 Watch closely: Even a 2–3 PSI drop indicates a leak.
Step 3: Inspect Every Joint & Connection
With the system under pressure, visually inspect:
- Solder joints (look for beads or moisture)
- Compression fittings
- Valve body seams
- Supply line connections
Use a dry paper towel—run it along joints. Any dampness = leak.
Step 4: Perform a Drain Water Test (Separate from Supply Test)
Remove the test plug and fill the tub with 2–3 inches of water. Let it sit 10–15 minutes.
- Check under the tub (use a flashlight and mirror if needed)
- Look at the subfloor and adjacent walls
This tests the drain assembly and overflow linkage—common leak points.
Step 5: Test the Diverter Function
Reattach the tub spout and showerhead (temporarily). Turn on water and switch between tub fill and shower 5–10 times.
- Does water leak from the spout when shower is on? → Faulty diverter
- Does water drip from ceiling or wall during shower mode? → Poorly sealed shower arm
✅ Pro move: Wrap the shower arm threads with 3–4 wraps of Teflon tape clockwise before final install.
Step 6: Document & Photograph
Take timestamped photos of:
- Pressure gauge reading at start and end
- All dry joints
- Water test in tub
This creates a liability shield if issues arise later—especially important for contractors.
Common Leak Sources in Combo Units (And How to Fix Them)
| Leak Location | Likely Cause | Quick Fix |
|---|---|---|
| Behind tub spout | Loose set screw or worn washer | Tighten or replace spout |
| Shower arm base | Poor thread sealant | Reapply Teflon tape, hand-tighten + 1/4 turn |
| Valve body | Improper soldering or O-ring fail | Re-sweat joint or replace cartridge |
| Drain flange | Putty not seated or cracked | Remove, clean, reapply plumber’s putty |
For deeper insight into plumbing materials and failure modes, see the Wikipedia entry on plumbing.
Mistakes to Avoid When Leak-Testing
- ❌ Skipping the pressure test because “it’s new plumbing”
- ❌ Using duct tape or rags to cap outlets (they can blow off!)
- ❌ Testing only hot or cold line—always test both together
- ❌ Rushing the drain test—10 minutes isn’t enough for slow seepage
Real-world case: A homeowner in Portland skipped testing. Six months later, mold covered 30 sq ft of drywall. Remediation cost: $7,200. The leak? A $2 washer in the spout.
How Long Should You Wait Before Installing the Surround?
After a successful 30-minute pressure test and 15-minute drain test with zero leaks, you can proceed immediately—as long as everything is dry.
But if you used plumber’s putty or sealants, wait 24 hours for full cure before sealing walls.
FAQ Section
Q1: Can I test the plumbing without the showerhead and tub spout installed?
A: Yes—but only for the supply pressure test. Cap the outlets with threaded plugs. However, you must install the spout to test the diverter function and check for spout leaks.
Q2: What pressure should I use for the test?
A: Match your home’s water pressure—typically 50–80 PSI. Never exceed 80 PSI, as it can damage valves. Use a gauge to confirm.
Q3: Is an air pressure test better than a water test?
A: Not for DIYers. Air tests require special equipment and are riskier (compressed air can cause explosive failures). Water is safer and more reliable for residential use.
Q4: My pressure dropped 5 PSI in 20 minutes—should I worry?
A: Yes. Even a small drop indicates a micro-leak, which worsens over time. Recheck all joints, especially soldered ones. Re-sweat if needed.
Q5: Do I need a permit to test plumbing before surround install?
A: In most U.S. jurisdictions, yes—especially if you altered pipes. The inspector will often require a witnessed pressure test before approving wall closure. Check with your local building department.
Q6: Can I use a moisture meter instead of a visual test?
A: You can, but it’s overkill for pre-install checks. Visual inspection + pressure hold is sufficient. Save moisture meters for post-install diagnostics.
Conclusion
Checking combo shower/tub plumbing for leaks before putting surround up is the single most cost-effective step in your bathroom remodel. It takes less than an hour, costs almost nothing, and could save you thousands in hidden damage.
Don’t gamble with water. Test thoroughly, document your work, and enjoy peace of mind knowing your beautiful new surround hides a dry, reliable system.
👉 Found this guide helpful? Share it with a friend planning a bathroom upgrade! A quick post on Facebook or Pinterest could save them from a plumbing nightmare.
Your future drywall—and your wallet—will thank you.
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