Tub spout leaks when washer runs

Quick Answer:

If the tub spout only drips or sprays while the washing machine fills, the leak is likely related to changing water demand exposing a weak diverter or worn seals. Do a simple test (run the shower alone, then start the washer fill) to confirm. If the leak is repeatable, the diverter or valve seals usually need attention or a plumber’s help.

Why This Happens

When the washer fills it temporarily shifts water flow and pressure in the home. A healthy diverter (the part that stops water from flowing out the tub spout when the shower is on) and good seals keep the spout closed under small pressure changes. If those parts are worn, the lower or changing pressure during a washer fill can let water pass out the spout.

Other causes can include a failing cartridge or valve inside the shower control, or uneven supply pressure between hot and cold. If the pattern looks different depending on where the washer is located, you may also want to check for localized supply issues such as a partially clogged line or a weak check valve. If you notice a similar pattern in another bathroom, see Leak only upstairs bathroom for related checks.

Step-by-Step What to Do

1. Observe the problem with a simple test

• Turn on the shower and let it run alone. Watch the tub spout for any drip or spray.
• Without changing the shower setting, start a normal washer fill cycle. Watch the tub spout again.
• If the leak appears only while the washer is filling, the issue is demand-related and likely tied to pressure changes or a weak diverter.

2. Check the diverter and visible seals

• Inspect the tub spout diverter (if you have a pull-up spout, look for looseness or wear). For cartridge-style valves, note any stiffness or unusual play in the handle.
• Clean around the spout and handle to remove mineral buildup that might prevent a full seal.
• If you recently serviced the valve and now see a leak when demand changes, consider the guidance in Leak after replacing diverter.

3. Test supply pressure and pressure balance

• While the washer fills, briefly run another tap in the house and watch how pressure changes. Large swings suggest supply or balancing problems.
• If you have a pressure gauge or can borrow one, measure static and dynamic pressure at an outside hose bib; large drops during the washer fill point to demand-related pressure change.

4. Small repairs you can try safely

• Tighten any loose spout set screws and re-seat the spout if it’s removable.
• Replace a worn rubber seat or O-rings if you can access them easily and are comfortable with a simple valve repair.
• If the diverter or cartridge is clearly worn, replacement is often the fix — but only if you can shut off water and follow the manufacturer instructions.

What Not to Do

• Don’t treat demand-related leaking as “just the washer”—it indicates weak seals; if repeatable, a plumber is appropriate.
• Don’t force or hammer the diverter or valve parts — that can break soft metal or plastic pieces and make the problem worse.
• Don’t use superglue, epoxy or temporary plugs to stop the leak without fixing the valve — those create harder repairs later.

When to Call a Professional

• The leak is repeatable when the washer runs and simple tightening or cleaning didn’t help.
• You can’t find or access the diverter, cartridge, or internal seals, or the repair requires removing the valve body.
• Your home shows large pressure swings affecting multiple fixtures, or you see other signs like banging pipes or major pressure loss.

Safety Notes

• Always shut off the water supply before removing a spout or valve cartridge.
• Protect the tub finish and drain when working on the spout—small parts can fall in the drain.
• If you’re unsure about turning off water or disassembling plumbing, stop and call a licensed plumber. Working on pressurized plumbing without experience can cause flooding and water damage.

Common Homeowner Questions

• Q: Will tightening the spout stop this?
  A: It can help if the spout is loose, but if the diverter or valve seals are worn the leak will likely return.
• Q: Can the washer be adjusted instead?
  A: Not really — the washer’s normal fill is expected. The plumbing should seal under typical pressure changes.
• Q: Is this an emergency?
  A: Usually not an immediate emergency, but you shouldn’t ignore persistent or repeatable leaks because they indicate failing seals that can worsen.