How to Test for a Faulty Mixing Valve in a Shower

water dripping from a shower head
What You'll Need
Adjustable wrench
Needle nose pliers
Clean rags
Petroleum jelly

The mixing valve mixes hot and cold water to provide consistent temperatures to your shower. A faulty shower mixing valve can make your shower both uncomfortable and ineffective. Follow these steps to test your shower to determine if it has a faulty mixing valve.

Step 1 - Isolate the Water Problem in Your Shower

The water problem in your shower could be: low water pressure, dripping faucet, a stiff handle, or either hot or cold water dispensing only.

1. Low Water Pressure

The mixing valve could be clogged, reducing the water pressure. Remove the valve and clear the clog. Replace any corroded or damaged pieces of the mixing valve. Lubricate the valve with petroleum jelly and reinstall.

2. Dripping Faucet

dripping shower head with tile wall background

If the faucet is dripping, the mixing valve ball is not seated properly in the valve stem to shut the shower handle off completely. Replace the mixing valve's plastic parts with brass parts.

3. Handle Doesn't Turn Smoothly

This means that the mixing valve is misaligned in the fixture. Remove the shower faucet handle and mixing valve, and check both for blockage and corroded surfaces. Replace the handle and any corroded valve parts.

4. Shower Emits Only Cold or Hot Water

This likely means that the mixing valve has become disconnected from the hot or cold water supply. Locate the supply pipes and reconnect them to the mixing valve.