Match the symptom to the part
| What happens | Likely part |
|---|---|
| Drips from the showerhead after use | Worn cartridge or valve seat |
| Water temperature swings | Cartridge or pressure-balancing valve |
| Weak spray or uneven spray | Clogged showerhead from scale |
| Water from the tub spout while the shower runs | Diverter that is worn |
| Tub holds water | Clogged drain, hair in the stopper or trap |
| Stain or drip on the ceiling below | Leak at the valve, the drain or a supply pipe |
Some of these are inexpensive. A showerhead can be soaked in vinegar to clear scale. Others need the wall opened.
The cartridge and the valve
Most modern shower valves use a cartridge, a plastic or brass insert that controls water flow and temperature. When it wears, it drips or stops mixing correctly. Replacing it is a repair measured in hours, but the right part must match the brand and model.
Older valves with separate hot and cold handles use washers and seats. They wear the same way, and a plumber can often rebuild them.
When the drain is the problem
Slow tub and shower drains are most often hair and soap in the stopper or trap. A plumber can clear it with a hand tool. If every drain in the bathroom is slow, the issue may be the branch line. See drain cleaning.
Leaks behind the wall
A shower valve is usually inside a wall, with an access panel on the other side or no panel at all. A leak there can run for weeks before a stain shows. If a ceiling below is stained, the plumber should look at the valve, the drain and the supply pipes. A leak detection visit can help locate the source.
Replacing a valve may mean opening tile. Ask where the opening will be made.
When to replace the whole valve
A cartridge swap fixes most drips. Replace the whole valve body when it is cracked, corroded or leaking from the body rather than the cartridge. Older valves may also lack modern temperature protection, and a replacement adds it.
If you are already opening a tiled wall, that is the time to replace the valve rather than patch it. A second opening later usually costs more than a slightly bigger first one.
Why the temperature swings
Most modern shower valves balance hot and cold pressure. When a toilet flushes or a washing machine fills, pressure drops on one line, and a worn balancing part lets the shower swing hotter or colder.
A new cartridge usually restores the balance. If the swing happens only while another fixture runs, tell the plumber, because that detail points to the valve and not to the water heater.