Interactive Photo Diagram
Tub & Shower Valve
The cartridge controls and mixes hot and cold water. A worn cartridge or related valve component can cause dripping, temperature problems, or difficulty controlling the water.
Reference checked: component relationships and terminology were reviewed against manufacturer documentation from Moen. This is original Classic Plumber educational artwork, not a manufacturer drawing.
Tap a numbered marker to learn what that part does.
Overview
Behind your shower handle is a mixing valve that blends hot and cold water to your chosen temperature. In modern showers, a single cartridge controls both flow and temperature. When that cartridge wears out, you get drips, temperature swings, or a handle that's hard to turn.
How It Works
When you turn the handle, the cartridge opens passages for hot and cold water. The mixture flows to the showerhead (or tub spout). When you close the handle, the cartridge seals. If the internal seals are worn, water drips from the showerhead even when off. Temperature fluctuations often mean the cartridge's balancing mechanism is failing.
Key Components
Valve Body
The brass body inside the wall. Hot and cold water enter here.
Cartridge
The replaceable internal valve. Controls flow and temperature. The most common wear part.
Hot Supply
Hot water from the water heater enters the valve.
Cold Supply
Cold water enters the valve.
Shower Outlet
Mixed water goes up to the showerhead.
Tub Spout (where applicable)
Mixed water goes down to the tub spout. A diverter redirects to the shower.
Common Issues
Temperature fluctuates
Failing balancing cartridge.
Handle hard to turn
Cartridge seized or mineral buildup.
Won't get hot
Cartridge, water heater, or cross-connection.
Maintenance Tips
- Note your shower valve brand (Moen, Delta, Kohler) — many offer free replacement cartridges.
- If the handle is stiff, don't force it — you can break the valve stem.
- Clean the showerhead annually by soaking in vinegar to remove mineral buildup.
- If you see water stains on the wall or ceiling below, there may be a leak behind the wall.
WARRANTY INFORMATION
Shower valve manufacturers (Moen, Delta, Kohler) often offer lifetime cartridge warranties for the original owner. If your shower drips or the temperature fluctuates, the cartridge may be free from the manufacturer — you only pay for labor if you hire a plumber.