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.
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.
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
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
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.
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.
Shut the Water Off
Turn off the water and close the drain stopper.
Take off the Handle
Remove the handle with the correctly sized Allen wrench. Remove the handle adapter with the Phillips head screwdriver.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
According to the U.S. Environmental Protection Agency, the average shower 2 1/2 gallons of water per minute. An on-demand water heater can supply 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.
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.
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.
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.
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.
Shields WC, McDonald E, Frattaroli S, Perry EC, Zhu J, Gielen AC. Still too hot: examination of water temperature and water heater characteristics 24 years after manufacturers adopt voluntary temperature setting. J Burn Care Res., vol. 34, no. 2, pp. 281-287, 2013. doi:10.1097/BCR.0b013e31827e645f
Uniform State Plumbing Code. Commonwealth of Massachusetts.
Showerheads. United States Environmental Protection Agency.
Carbon Monoxide Poisoning Prevention. Centers for Disease Control and Prevention.