Hot and Cold Water Not Mixing in Shower (Causes & Solutions)

The daily shower should be one of those relaxing moments when you refresh and shake off stress. Taking a shower has been shown to improve immune function, increase blood flow, lessen fatigue, and ease muscle aches. However, there can be issues preventing you from enjoying the amazing benefits of showers. One of those unpleasant situations is hot and cold water not mixing in shower.

Unless you like cold showers or scalding water, you will not find this acceptable.

A fussy shower faucet is a trivial problem, yet it prevents you from getting an excellent start of your day.

This post is about the multiple causes of hot and cold water not mixing in the shower. We will also advise you on what you can do about it.

Possible causes of hot and cold water not mixing in shower and solutions


So, you are tired of being either blasted with cold water or scalded with hot water? There are a few possibilities to explore if you want to solve your problem once and for all.

1.There is not enough hot water in the heater

If water temperatures fluctuate while trying to have a shower, the culprit could be the water heater. Possible causes of getting out of hot water are:

  • Being the last in line for a shower
  • The water heater being too small for your needs
  • Not using a water flow restrictor

Make sure you have plenty of hot water in the heater before taking a shower. Otherwise, the water will be very hot in the beginning and cold afterwards.

2.The dip tube in the heater tank is faulty

Another possible cause of the problem also lies into your water heater. This hypothesis applies when you have a tank-based heater. Also, the water temperature needs to be inconsistent at any service point in your house.

There are two pipes on top of your water heater tank. The longer one extends to the bottom of the tank and forces cold water downwards. The other tube is shorter and draws hot water from the top of the tank. This system is based on the phenomenon of hot water rising and cold water going to the bottom.

When the dip tube is defective (cracked, corroded, has holes, has snapped off), cold water mixes with hot water. As a result, you get inconsistent temperatures or lukewarm water. [2]

You don’t have to replace the entire water heater. Actually, it is sufficient to replace the dip tube only.

3.Blockages in on-demand water heaters

On-demand water heaters produce hot water on the spot while also holding a small reserve. A high demand for hot water can deplete the heater’s supply. Even if water is also heated on the spot, the heater will fail to provide enough hot water. The result – you will experience temperature inconsistences, such as hot and cold water not mixing in shower.

One issue could be the heater’s low capacity, in which case you will need a larger heater. Or resuming to using one hot water appliance at a time.

Another possibility is having blockages in the water heater. The heater may not be able to heat water due to deposits such as rust, carbonates, and oxides. You can use a descaler kit every 12 to 18 months to eliminate mineral deposits. A good kit can cost as high as $200 dollars, but they are worth the money if you want to maintain your heater in good condition.

Beware of multiple and severe blockages as they can be dangerous. Blocked vents can cause carbon monoxide leaks into your home. Carbon monoxide is an odorless and potentially deadly gas.

Checking for vent blockages regularly, especially when you have an older heater, is very important.

4.The cold-water sandwich phenomenon in tankless water heaters

The powerful heat exchangers of tankless water heaters make it possible to rapidly heat water flowing through their system. They activate automatically when you start a hot water faucet.

The cold-water sandwich phenomenon happens when the heater activates and deactivates frequently within a short period of time. Hot water takes a while to cool down, and when you use the hot water again, the latent warm water ejects first. Next you have a brief period of cold water coming from water pipes servicing your home. The cold water only lasts for a few seconds.

You will not notice this when filling the bathtub. On the other hand, when taking a shower, the cold-water sandwich can be very unpleasant.

Solutions to tackle this problem are:

  • Using a recirculating pump
  • Installing a storage tank heater
  • Replacing the water heater with a newer model (cold-water sandwich is a bigger problem in older tank heaters).

5.The scald guard needs to be adjusted

This small plastic disk plays a significant role in keeping you safe. It is a must-have in homes with children and elderly people. There is one disadvantage, though – not adjusting it correctly can mess with your water temperature.

Loosen the screws of the scald guard with a wrench and lift it from the faucet. Adjust the valve gradually and don’t make the hot water limit too high. Test the water temperature before using the shower. These guards exist for a good reason and they should be used as intended.

6.The faucet cartridge is worn out

Adjusting the scald guard is a good opportunity to take a look at the faucet cartridge. Does it look too old and worn out? Don’t be surprised – plumbing parts fail in time due to usage.

In some cases, a cartridge that has been in place for a long time can be crusted with hard water deposits.

Replacing it can be difficult, but may be the only solution to hot and cold water not mixing in shower.

You are using a single-control lever

Many shower faucets use a single-control lever. It is practical and simple to use, but there is a problem with this type of faucet. [2]

The single-control lever shower faucet most likely uses a pressure-balancing mixing valve.

The role of the mixing valve is to mix hot and cold water so you obtain the desired showering temperature.

However, there is a disadvantage when it comes to using a pressure-balancing mixing valve to adjust your water temperature.

These valves do not actually control the temperature of shower water. What they do is adjust the ratio of cold and hot water pressure. The act is purely mechanical.

This system comes with two disadvantages:

  • You can get scalded

Shower water can get as hot as the water stored in the water heater if you push the lever to the extreme left. This is very dangerous for children and aged people.

  • It is difficult to find the right shower temperature

Every shower routine starts with a guessing game since the ratio of cold to hot water is never the same. This happens because the temperature and amount of hot water in the heater can differ.

The solution?

Switch to a thermostatic mixing valve.

This type of valve comes with two handles. One is to control the pressure of the water and the other is to control water temperature.

Benefits of a thermostatic mixing valve

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This type of valve works much like a pressure-balancing valve as it also mixes hot and cold water. The difference is it senses the temperature of the water and controls it. This way, you easily get precise shower water temperatures. However, there are also other benefits aside from maintaining the right shower temperature:

  • Eliminating scalding temperatures

It is possible to pre-set thermostatic mixing valves to reach your desired maximum temperature. You can set the shower temperature to never exceed a certain value, such as 105 degrees Fahrenheit. This way you will prevent serious accidents and make your home a safer place.

  • Easy to control water flow

This type of valve allows you to easily increase or decrease water flow. For instance, you can conserve water while soaping up and increase volume again for rinse off.

  • Preventing drops in water pressure

Have you noticed how water pressure drops when other water appliances are being used? This will no longer be the case with thermostatic mixing valves as they maintain water pressure levels constant.

The only drawback of thermostatic mixing valves is the higher price. Given the advantages, it is definitely worth spending that extra money. You will enjoy increased comfort, control, and safety.


Multiple causes candidate for the title of culprit for hot and cold water not mixing in shower. Areas to investigate are water heater limitations and defects, and malfunctioning valves. Switching to a thermostatic mixing valve often represents the solution to this annoying problem.