You pull up the diverter knob or flip the lever to fill the tub, and instead of all the water flowing through the spout, some of it keeps trickling — or even streaming — out of the shower head. It's annoying, it wastes water, and it makes you wonder if something is seriously wrong with your plumbing.
Here's the short answer: almost always, this is your diverter valve. The diverter is what redirects water from your tub spout up to the shower head. When you want to fill the tub, it's supposed to seal off the path to the shower. When the diverter wears out, that seal weakens, and water finds its way through anyway.
A small amount of water coming from the shower head when filling the tub is actually normal, even on a newer diverter. Perfect sealing is nearly impossible to achieve with these simple mechanical parts. But if you're getting a steady stream, if the water from the shower head is soaking your tile, or if the flow to the spout feels weak, that's a worn-out or failed diverter — and it's worth fixing.
How a Diverter Valve Works
Before you can diagnose the problem, it helps to know which type of diverter you have. There are three common setups.
The pull-up knob on the tub spout is by far the most common arrangement in older homes and many apartments. A small plastic or rubber gate inside the spout lifts when you pull the knob, blocking the path to the tub and redirecting pressure up to the shower line. When this gate wears down, it no longer forms a tight seal.
A three-way diverter is mounted in the wall between your hot and cold handles. You turn or press a separate handle to switch between the tub and shower. This type has more moving parts inside the wall and is more involved to repair.
The single-handle diverter is built into the main valve cartridge in modern single-handle tub-shower combos. Turning or pulling the main handle both controls temperature and diverts the flow. When the cartridge wears out, the diversion function goes with it.
3 Reasons Water Keeps Coming From the Showerhead
1. The Tub Spout Diverter Is Worn Out
This is the most likely culprit if you have a pull-up knob on your tub spout. Over time, the rubber or plastic gate inside the spout degrades. It might crack, compress, or simply stop springing back to its fully lifted position. The result is a partial seal that lets water slip through to the shower line even while you're filling the tub.
The fix here is usually to replace the entire tub spout. Spouts are not generally designed to be opened and repaired — the cost of a new one is low enough that replacement is almost always the right call. You can find a replacement at any hardware store for $15 to $40 depending on the finish and style.
2. Mineral Buildup Around the Diverter
If you live in an area with hard water, calcium and limescale deposits can build up inside the tub spout around the diverter gate. Over time, enough buildup can physically prevent the gate from fully closing, leaving a gap that lets water through.
You may be able to see white or yellowish crusty deposits around the spout opening or on the pull knob itself. Soaking the spout with white vinegar can sometimes dissolve light scale. But in many cases, the buildup is internal and harder to address without disassembly. A straightforward replacement is often easier and more permanent.
3. The In-Wall Diverter Valve or Cartridge Has Failed
If you have a three-way diverter handle on the wall, or a single-handle setup, and water is still coming out of the shower head while filling the tub, the issue is likely inside the wall. The cartridge or diverter mechanism inside the valve body has worn out or failed.
Signs that this is your problem: the diverter handle feels loose or spins without clearly redirecting water, or water comes out of the shower head no matter what position the handle is in. In some cases you might hear a hissing or rushing sound in the wall even with the diverter in the tub position.
This type of repair is more involved. The cartridge type varies by valve manufacturer, and accessing it requires shutting off the water supply and working inside the valve body. This is generally not a DIY job for most homeowners.
Can I Fix This Myself?
For a pull-up tub spout diverter, yes, replacing the spout is very manageable. Most tub spouts attach in one of two ways: they either thread onto a pipe nipple coming out of the wall, or they slide onto a copper stub-out and lock with a set screw on the bottom. Turn off the water or work quickly (the spout is usually the last connection before the end of the line), remove the old spout, and install the new one. The whole job takes 30 minutes or less and costs $15 to $40 in parts.
For an in-wall diverter, this is a different situation. You need to shut off the water to the entire bathroom, remove the handle and trim, and extract the cartridge from inside the valve body. Cartridges are not universal — a Moen cartridge is different from a Delta, different from a Kohler — and installing the wrong part or seating it incorrectly can cause bigger problems than the one you started with. Most homeowners are better off calling a plumber for this one.
How Much Does a Diverter Repair Cost?
If you're replacing a tub spout yourself, expect to spend $15 to $40 on parts and about 30 minutes of your time. That's a very manageable DIY project.
If the diverter is in the wall and a plumber handles it, a typical in-wall diverter cartridge replacement runs $150 to $300 or more, depending on the valve brand, cartridge availability, and how easy the valve is to access. Proprietary cartridges from certain manufacturers can push that number higher.
One important note: if the valve is behind a tile wall with no existing access panel, and the tile has to be opened to reach it, costs increase significantly. This is relatively rare but worth asking about before the work begins.
When Should You Call a Plumber?
Some situations clearly call for professional help.
Call a plumber if you've already replaced the tub spout and water is still coming out of the shower head. That tells you the problem is upstream in the wall, not in the spout itself.
Call a plumber if your diverter is an in-wall three-way valve or part of a single-handle cartridge system. These are not designed for casual DIY repair.
Call a plumber if the pull-up knob is stuck, broken off at the base, or spins freely without redirecting water. That can indicate a more significant failure inside the spout or the connection behind it.
Call a plumber if you hear hissing or rushing water sounds in the wall even when the diverter is in the tub position. That can mean water is moving somewhere it shouldn't be.
And call a plumber right away if you notice any signs of water damage near the tub: staining on the wall, soft or bubbling drywall, discoloration on the ceiling below, or a musty smell. A diverter that's been leaking inside the wall for a while can cause real structural damage.
A worn diverter is usually a straightforward fix, but it's worth getting it right. If you're not sure which type of diverter you have, or if the DIY route hasn't solved the problem, Rooter Hero Plumbing & Air can help. Our plumbers are available 24 hours a day, 7 days a week, with same-day service and no extra fees for nights or weekends. Call us at (866) 941-8214 and we'll get it sorted out.
