How to Fix Inconsistent Water Temperature

Testing temperature on running water from shower head

The Spruce / Kevin Norris

Project Overview
  • Working Time: 1 hr
  • Total Time: 1 hr, 30 mins
  • Skill Level: Intermediate
  • Estimated Cost: $25 to $200

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. Here are a few ways to mitigate the problem.

Warning

Novice DIYers should not attempt to perform repairs or work on their hot water heater. Projects of this sort are best left to professionals and those with extensive experience applying the necessary skills. If you are a beginner, use this guide as an overview of assessing the cause of the issue and call a professional to complete the necessary repairs.

What You'll Need

Equipment / Tools

Valve Cartridge Replacement

  • Phillips head screwdriver
  • Set of Allen wrenches
  • Adjustable pliers
  • Needle-nose pliers
  • Shower cartridge puller tool

Dip Tube Replacement

  • Pipe wrench
  • Crescent wrench
  • PEX pipe cutter or hacksaw
  • Copper pipe cutter or hacksaw
  • Channel lock pliers

Materials

Valve Cartridge Replacement

  • Replacement shower valve cartridge

Dip Tube Replacement

  • 1 52-inch polypropylene flared dip tube
  • 2 1/2-inch push-fit connectors
  • Teflon tape
  • 1 1/2-inch flexible braided line

On-Demand Water Heater Descaling

  • Complete on-demand water heater descaling kit with solution, bucket, hoses, and pump

Instructions

Inconsistent Shower or Bathtub Water Temperature

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.

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. Many older homes without pressure-balanced or thermostatic controls must have the current valves replaced anyway: Most major cities no longer allow the installation of non-pressured balanced valves.

Warning

This guide offers a general solution for situations where you have a pressure balance valve or TMV already installed. Find the manufacturer and model of your current product for replacement parts.

  1. Shut the Water Off

    Turn off the water and close the drain stopper.

    Water supply turned off by turning shutoff valve

    The Spruce / Kevin Norris

  2. Take off the Handle

    Remove the handle with the correctly sized Allen wrench. Remove the handle adapter with the Phillips head screwdriver.

    Allen wrench removing shower handle

    The Spruce / Kevin Norris

  3. Replace the Cartridge

    Gently pull out the metal clip holding the cartridge in place. Slide the new cartridge in place, with its hot side on the left. Replace the cartridge retainer clip.

    New shower handle cartridge placed in wall

    The Spruce / Kevin Norris

  4. Install the Guard and Handle

    Install the scald guard. Turn the water back on and adjust the scald guard while the water is running. Replace the handle.

    Scald guard place over cartridge to replace shower handle

    The Spruce / Kevin Norris

Faulty Water Heater Dip Tube Causing Inconsistent Temperatures

Another common reason 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 tube can be faulty in several ways. It can snap off entirely at any place. It can also be cracked, corroded, or develop holes at any point along the length. When any of these issues occur, incoming cold water mixes with hot water. The result is inconsistent temperatures or sometimes consistently lukewarm water. Instead of replacing the water heater, you can inexpensively replace the dip tube itself.

Warning

Replacing a water heater dip tube—as with many projects or repairs involving water heaters—is best left to professionals. If you do not have extensive experience with the skills necessary to complete this project, do not attempt it and call a professional to do the repairs.

  1. Prep the Water Heater

    Turn off the gas or electric supply to the water heater. Drain the water heater (which adds time to this project).

    Water heater gas line turned off

    The Spruce / Kevin Norris

  2. Remove the Vent Stack

    With the Phillips head screwdriver, remove the vent stack at the top of the water heater and the metal shield attached to the water heater.

    Warning

    Work with caution and do not hesitate to call a professional should something go wrong while you're working with major parts of the water heater.

    Vent stack removed from top of water heater with Phillips head screwdriver

    The Spruce / Kevin Norris

  3. Unscrew and Separate Union

    Using channel lock pliers, unscrew and separate the dielectric union.

    Alternately, if you are working with copper pipe, you can use a copper pipe cutter or hacksaw to cut the copper pipe about 8 inches above the water heater.

    Dielectric union unscrewed with channel lock pliers

    The Spruce / Kevin Norris

  4. Remove the Union Fitting

    Stabilize the dip tube fitting with the pipe wrench while turning off the dielectric union with the crescent wrench. Remove the union fitting and set it aside.

    If you are working with a copper line fitting, 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.

    Union fitting removed with wrench on top of water heater

    The Spruce / Kevin Norris

  5. Remove the Dip Tube

    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.

    Tip

    When pulling the dip tube out, if it hits the ceiling and gets stuck (if the ceiling is low, for example), you will have to lay the tank down to remove the tube completely.

    Dip tube removed from top of water heater

    The Spruce / Kevin Norris

  6. Prepare the New Dip Tube

    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.

    PEX cutter cutting replacement dip tube

    The Spruce / Kevin Norris

  7. Install the New Dip Tube

    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.

    New dip tube inserted through top of water heater

    The Spruce / Kevin Norris

  8. Finish Installation

    Wrap the nipple with plumbers tape. Reinstall the dielectric union and reattach pipes.

    If working with copper piping, connect the two severed copper pipes with the flexible braided 1/2-inch line, using the 1/2-inch push-fit connectors.

    Reinstalled dielectric union connected to pipe

    The Spruce / Kevin Norris

Inconsistent Water Temperatures With On-Demand Water Heaters

On-demand water heaters, 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 it is needed. With tank-based heaters, even if no hot water is used, the heater still maintains that water at a consistent temperature. 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, and an on-demand water heater can supply 2 1/2 to more than 10 gallons of hot water per minute, depending on the model. The need for hot water can still quickly outstrip a on-demand water heater's supply, though new models of on-demand water heaters can be installed in parallel to fulfill a larger hot water demand. Even so, there might still be temperature inconsistencies.

  1. Descale the Heater

    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.

    Descaling kit for on-demand water heater

    The Spruce / Kevin Norris

  2. Check for Blockages

    Vent pipes may be blocked by nests, vermin, or other debris, affecting the heater's ability to operate. Examine and clean out all vents that extend to the home's exterior.

    Warning

    If there are multiple or severe blockages, take note: These can be very dangerous. Blocked vents can lead to carbon monoxide leakage into your home. These gases are odorless and can be deadly.


    If you have an older heater, plan to check for vent blockages regularly and consider replacing the heater with a newer model. Newer heaters and instantaneous heaters usually come with a safety switch called a spill switch. These shut down the heater when a blockage or backdraft occurs to prevent any carbon monoxide leakage.

    Pipes outside of house venting cloudy smoke

    The Spruce / Kevin Norris

  3. Analyze Your Water Demands

    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 your current heater with an on-demand water heater with greater output.

    Tip

    If your inconsistent water temperature problem is specifically a cold water sandwich, first check to make sure there are no crossed connections between hot and cold water lines. This can happen after a new appliance or plumbing fixture has been installed. (Something as simple as a bad washing machine solenoid valve can cause this issue.)


    If you're experiencing cold water sandwiches and you have had recent work done, shut the water (hot and cold) off to the machine in question and see if that fixes the problem. If it does, contact whoever installed the machine and have them fix the crossed connections.

    On-demand water heater showing water temperature

    The Spruce / Kevin Norris