Quick Answer:
If the tub spout flows weakly while nearby sink faucets are fine, the issue is often in the spout or the diverter path rather than your whole house supply. Start by confirming the problem affects only the tub spout, test the shower setting to compare the two water paths, and—if the spout is removable—take it off to inspect for a stuck washer or debris. If the spout is corroded or the diverter is seized, call a plumber.
Why This Happens
Possible causes include a clogged spout, a loose or damaged washer inside the spout, mineral buildup or debris trapped in the diverter, or an internal diverter mechanism that’s not seating correctly. Because the sink and tub can use different fittings or paths, sinks can look normal even when the tub spout is restricted.
If the weak flow started suddenly after a change to plumbing or a repair, it can also point to trapped debris or an adjustment problem—see related notes like Shower pressure suddenly dropped and Shower low pressure after plumbing repair for other common patterns.
Step-by-Step What to Do
Confirm the problem is only at the tub spout
- Run the sink faucet(s) on the same water line and note flow. If sinks are full flow and the tub spout is weak, the issue is likely local to the tub spout or diverter.
- Turn water fully on to the tub spout and pay attention to whether hot and cold behave the same. If one side is worse, that narrows the search to that cartridge or valve area.
Test the shower mode to compare paths
- Switch the diverter to shower mode (if applicable) and check showerhead flow. If the showerhead has normal pressure but the tub spout is weak, the diverter may be routing most water away or the spout itself is blocked.
- If both spout and shower are weak, the problem may be upstream (valve/cartridge, or debris in the line).
Remove the spout (if accessible) and inspect
- Identify the spout type: slip-on (secured with a set screw) or threaded. For slip-on, loosen the small screw under the spout, then pull the spout straight off. For threaded spouts, unscrew by turning counterclockwise.
- With the spout removed, inspect for a loose washer, torn rubber, mineral encrustation, or visible debris. A torn or missing washer can reduce flow.
- Flush the pipe briefly by running the tub valve with the spout off to clear loose debris—hold a rag or cup to direct the water. Keep the flow brief and watch temperature to avoid scalding.
- If you find a loose washer or debris, clean or replace the washer and remove mineral buildup. Replace the spout and test flow.
Reinstall and test
- Reinstall the spout correctly (tighten the set screw or thread it back on). Turn the valve on and test both tub fill and shower mode again.
- If the spout was clean and flow is still weak, the diverter or valve cartridge may be faulty or partially blocked and may need further service.
What Not to Do
- Don’t try to “boost” tub fill by removing internal parts from the spout or diverter incorrectly. Forcing pieces can break components or create leaks.
- Don’t apply excessive force or heat to a stuck spout—this can damage the pipe or finish. If the spout is corroded or seized, a plumber is appropriate to avoid damaging the plumbing.
- Don’t ignore hot-water temperature when flushing lines—run a small, controlled flow and be careful to avoid scalding.
When to Call a Professional
- If the spout is corroded, stuck, or won’t come off without excessive force.
- If you remove the spout and the problem continues (diverter or valve cartridge may need inspection or replacement).
- If you find damaged plumbing, persistent leaks, or you’re uncomfortable shutting off or working on the valve—call a licensed plumber.
Safety Notes
- Be careful of hot water when testing or flushing lines. Run short tests and check temperature before full exposure.
- Turn off water at the fixture or main if you need to work longer or remove more than just the spout. Know where your shutoff is before starting.
- Use basic hand tools and avoid heavy force. If a part won’t move with normal tool use, stop and consult a professional to prevent damage.
Common Homeowner Questions
- Q: Can mineral buildup cause weak flow at the spout?
A: Yes. Calcium and debris can clog the spout or diverter and reduce flow. - Q: Is replacing the spout an easy DIY fix?
A: Often yes for a removable spout with a set screw or threaded connection, provided it isn’t corroded or stuck. - Q: Will cleaning the spout always fix the problem?
A: Not always—if the diverter or valve is clogged or damaged, cleaning the spout may not restore full flow.