How to Fix Inconsistent Water Temperature

Shower Head

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Inconsistent water temperature in your home can be annoying and even dangerous. Showering under comfortable warm water that unexpectedly turns cold is a rude awakening. It's frustrating to draw what you believe to be cool water from a tap, only to find warm water flowing into your drinking glass. And when that water reaches high enough temperatures to scald, it is dangerous. Any of several different scenarios might be the driver behind your home's inconsistent water temperature, or several may be working in concert to cause the issue.

Project Metrics

  • Working Time: 60 minutes
  • Total Time: 90 minutes
  • Skill Level: Intermediate
  • Materials Cost: $25 to $180

Tools and Supplies You Will Need

For Valve Cartridge Replacement

  • Phillips head screwdriver
  • Allen wrenches, set
  • Adjustable pliers
  • Needlenose pliers
  • Replacement shower valve cartridge
  • Shower cartridge puller tool

For Dip Tube Replacement

  • 52-inch polypropylene flared dip tube
  • Pipe wrench
  • Crescent wrench
  • Phillips head screwdriver
  • PEX pipe cutter or hacksaw
  • Copper pipe cutter or hacksaw
  • Teflon tape
  • Flexible braided 1/2-inch line
  • Two 1/2-inch push-fit connectors

For On-Demand Water Heater Descaling

Purchase a complete on-demand water heater descaling kit with solution, bucket, hoses, and pump.


Inconsistent Shower or Bathtub Water Temperature Only

It may be the most common and well-known cause of inconsistent water temperatures: another water demand is initiated elsewhere in the house, thus affecting the temperature of the water flowing from your tap. When a dishwasher turns on or a toilet is flushed, there is a new demand for water placed on the system. Since the system is central to all of your home's services, all must share both the cold and hot water.

Yet pressure-balanced and thermostatic shower/tub controls are designed to counteract that problem. Replacing the shower cartridge is often the best way to fix inconsistent water temperatures.

  1. Turn off the water and close the drain stopper.
  2. Remove the handle with the correctly sized Allen wrench.
  3. Remove the handle adapter with the Phillips head screwdriver.
  4. Gently pull out the metal clip holding the cartridge in place.
  5. Slide the new cartridge in place, with its hot side on the left.
  6. Replace the cartridge retainer clip.
  7. Install the scald guard and adjust it while the water is running.
  8. Replace the handle.

Faulty Water Heater Dip Tube Causing Inconsistent Temperatures

One of the most common reasons why you may be experiencing inconsistent water temperatures at any service point in your house is that your conventional tank-based water heater's cold water dip tube is faulty.

On top of your water heater are two pipes that extend into the water heater. One dip tube extends almost to the bottom of the tank and forces cold water to the bottom. The other dip tube is shorter and it draws hot water from the top of the tank since hot water rises. The cold water can be faulty in several ways: it can snap off entirely at any place or it can be cracked, corroded, or develop holes at any point in his length. When this happens, incoming cold water mixes with hot water and the result is inconsistent temperatures or sometimes entirely lukewarm water. Instead of replacing the water heater, you can inexpensively replace the dip tube itself.

  • Turn off the gas or electric supply from the water heater.
  • Drain the water heater.
  • With the Phillips screwdriver, remove the vent stack at top of the water heater and the metal shield attached to the water heater.
  • Use the copper pipe cutter or hacksaw to cut the copper pipe about 8 inches above the water heater.
  • Stabilize the dip tube fitting with the pipe wrench, while turning off the copper line fitting with the Crescent wrench.
  • Remove the copper fitting and set it aside.
  • Use the pipe wrench to turn the dip tube fitting off. When it is free, use your hands to pull the dip tube straight up and out of the water heater.
  • With the PEX cutter or hacksaw, cut the replacement dip tube so that it is about 3 inches short of the bottom of the water heater.
  • Slide the new dip tube straight down into the water heater.
  • Wrap the threads with Teflon tape, then screw the fitting into place with one of the wrenches.
  • Connect the two severed copper pipes with the flexible braided 1/2-inch line, using 1/2-inch push-fit connectors.

Inconsistent Water Temperatures With On-Demand Water Heaters

On-demand, or tankless, water heaters are energy-savers since they do not heat a large amount of water (often over 55 gallons) to be held in reserve for whenever hot water is needed. With tank-based heaters, even if no hot water is used the heater still maintains that water at a consistent temperature. Instead, on-demand water heaters heat water on the spot, as needed.

The average shower uses between 1-1/4 and 2-1/2 gallons of water per minute; an average on-demand water heater can supply 3-1/2 gallons of hot water per minute. The need for hot water can quickly outstrip on-demand water heaters' supply.

  1. Carbonates, rust, oxides and other mineral deposits may be hampering the heater's ability to heat the water. Use a descaler cleaning kit every 12 to 18 months to rid the system of mineral deposits. Descaling kits are expensive, ranging from $140 to $200, but they are worthwhile for preserving the life of your on-demand water heater.
  2. Vent pipes may be blocked by nests, vermin, or other debris, affecting the heater's ability to properly operate. Examine and clean out all vents that extend to the home's exterior.
  3. When the heater runs hot, then cold, then hot again, it is referred to as a cold water sandwich. Two water demands have been placed on the system back-to-back. Either space out the water demands or replace with an on-demand water heater with greater output