Quick Answer:

If water stays coming from the tub spout and won’t switch to the shower head, the diverter (the valve or mechanism that routes water) is likely stuck, clogged with mineral debris, worn out, or not getting enough flow to lift. Start with simple checks: increase flow briefly, look for debris, and clean the shower head and spout. If the diverter is visibly damaged or still won’t hold water after cleaning, replacement is often the easiest fix.

Why This Happens

Common causes are:

• Mineral buildup or small debris blocking the diverter’s movement.
• Insufficient flow or pressure — if flow drops, the diverter may not lift fully. If only one fixture seems weak, check that first; see one faucet has low water pressure for related checks.
• Mechanical wear: the tub spout diverter (pull-up or push-down style) can wear out, or the internal diverter cartridge can corrode or strip.
• Loose or broken parts in the faucet trim or tub spout that prevent a full seal, so water keeps flowing to the spout even when diverted.

Step-by-Step What to Do

1. Try increasing the flow briefly

Sometimes the diverter needs a bit more force to lift. Turn the tub faucet handles fully on (or move the single-handle to full flow) for a few seconds and try the diverter. If the shower engages, reduced flow or a partially closed supply was the issue. Don’t leave full flow on for long — this is a diagnostic step only.

2. Check the tub spout diverter for wear

Inspect the tub spout diverter (if you have a pull-up or push-down spout):

• Look for cracks, loose parts, or a spout that wiggles. If the spout turns or slides easily, the internal diverter may be worn.
• Signs that replacement is needed: water continues to run from the spout when the diverter is up, rough or sloppy motion, visible corrosion, or a spout outlet that drips even when switched.
• Many spouts are either slip-on (pulled off) or threaded (unscrew). Remove it carefully to inspect the internal mechanism.

3. Check the diverter for debris and clean it

Debris and mineral deposits often stop the diverter from seating or moving. Steps to clean:

• Turn off the water supply or at least be ready to stop water quickly. Place a towel or bucket under the spout.
• Remove the tub spout or access the valve trim (depending on your model). Use a soft brush or cloth to clear visible debris.
• Rinse the diverter area by briefly opening water to flush out loosened particles, then test the diverter.

4. Clean the shower head

A shower head clogged with minerals can mask whether the diverter is working. Remove the shower head and soak it in white vinegar for 20–30 minutes, then scrub with an old toothbrush and rinse. Reinstall and test the diverter again.

5. Replace the diverter if needed

If cleaning doesn’t fix it and you saw wear or damage, replace the diverter or tub spout. Replacement signs include persistent leaking from the spout, stripped splines, or irreparable corrosion. For valve-style diverters, replacing the cartridge may be required. After reinstalling parts, carefully restore water and turn water back on slowly to check for leaks and proper operation.

What Not to Do

• Do not pry aggressively — forcing parts can break trim, cartridges, or tiles.
• Do not use harsh chemicals — strong drain or limescale chemicals can damage finishes and seals.
• Do not force a stuck diverter until it breaks — breaking a diverter often makes the repair harder and more expensive.

When to Call a Professional

• If you can’t access the diverter without removing significant trim or tile.
• If replacing the cartridge or valve is necessary and you’re not comfortable disassembling the plumbing—it may require shutting off and draining the full supply lines.
• When leaks continue after cleaning or replacement, or if you see water damage behind walls.

Safety Notes

• Turn off water at the shutoff valves if you’ll remove parts, and have a bucket or towels ready for drips.
• Protect finishes: wrap jaws or tools with cloth when removing chrome spouts or handles.
• Use mild cleaners (vinegar and a brush) rather than strong acids. After any repair, open the water slowly to check for leaks and proper function.

Common Homeowner Questions

• Why does water trickle from the tub spout while the shower is on?
  Because the diverter is not sealing fully—often due to wear, debris, or damaged seals.
• Will soaking the spout in vinegar damage finishes?
  No — short soaks and gentle brushing are safe; avoid harsh acids or prolonged exposure on plated finishes.
• Can I replace the diverter myself?
  Yes for most tub spout replacements and simple cartridge swaps, but complex valve work or concealed plumbing is best left to a pro.