Hot Water Backflow Into Cold? (Easy Fixes, Tips & More)

By - Ron Singh

Updated -

Published -

Are you wondering why hot water is coming out of your cold tap? Many households face this problem, known as hot water backflow into the cold.

In this article, I will tell you the common reasons why hot water comes out of your cold tap and how to resolve this issue.

Hot water backflows into cold

  • The hot water and cold water pipes are close to each other.
  • The ventilation ducts are close to the cold water pipes. 
  • Incorrect installation of heat trap.
  • High pressure of water.
  • Faulty thermostats
  • Heated water tanks.
  • Recirculating plumbing.

Can Hot Water Backflow Into Cold?

Hot Water Backflow Into Cold

Hot water can cause backflow into a cold water tap, and it is dangerous if you put it on your cold faucet and get burned by hot water. Hot water back flowing into cold can be a result of:

#1. Closeness Of Pipes

If the pipes are too close, the heat from the hot pipe can affect the cold water pipes. 

#2. Ventilation Ducts 

The surface of the ventilation ducts can touch the cold pipes if they are close to each other.

#3. Bad Thermostats

In a water expansion tank, the thermostat can become faulty. The malfunctioning of the thermostat will make the water overheat, and it will flow out of the cold faucet. 

#4. Heating Effect

Copper is a heat conductor. Therefore, if you have copper pipes,  the water that flows through the faucet can heat up and make hot water backflow into the cold. The best way to resolve this issue is to contact a plumber.

Why Is My Hot Water Getting Cold Fast?

#1. Bad Heating Element

Faulty heating elements are one reason why your hot water gets cold fast. When the heating element does not function properly, it will not heat water in the tank.

As a result, your water will get cold fast, or the water will not be cold at all. 

First, check the voltage of the heating element with a continuity tester to find out what the problem is. Contact a professional if you do not know how to carry out this test.

#2. Small Water Heater

The size of the water system plays a massive role in this issue. If the water system is too small to meet the demands, it will not be able to supply hot water.

Smaller tanks can only hold a small quantity of hot water at a time. You can also run out of hot water if you shower for too long. 

If the demand exceeds the water heater’s capacity, your water will get cold quickly. Therefore, ensure the hot water tank is large enough to meet your demands.

#3. Faulty Thermostats

Every water heater has a thermostat. This thermostat sends signals to the heating elements.

The element at the top heats up first before the lower one. If the thermostat is faulty, it can make your hot water turn cold quickly.

#4. Old Water Tanks

When a tank becomes too old, it begins to malfunction. Consider changing your old tanks. 

#5. Broken Dip Tubes

The dip tube connects the cold water inlet to the bottom of the tank. The function of this tube is to deposit cold water beneath the heater.

During this process, the hot water rises to the top and flows through the hot water outlet. 

If this tube breaks, the cold water fills the tank and flows out with the hot water. Change the dip tube if this is the case.

#6. Accumulation Of Dirt

Dirt buildup is one of the reasons your hot water gets cold quickly. When water moves through the pipes, it carries solid materials.

These materials settle below the hot water tank and cause an accumulation of dirt. 

Even if there are filters to remove impurities, calcium, magnesium, and iron still gets into the inlet. This buildup takes space, and there will not be enough space for hot water in the tank.

In addition, the buildup makes the water lose its heating capacity. Getting rid of this dirt is the only solution to this problem.

#7. Poor Maintenance

Periodic inspection leads to this issue. Water heaters need maintenance and are regularly inspected and fixed for every fault.

How to Fix Hot Water Backflow Into Cold?

To fix hot water back flowing into cold,

#1. Turn Off Water Supply

Before attempting any DIY plumbing repair, turn off the water supply to avoid significant water leaks. Then, drain the water out of the pipes to remove excess water in the pipe.

#2. Inspect the Cartridge

Check the cartridge to know if it is damaged. If it is damaged, it can misdirect the water supply.

Replace it by unscrewing the faucet, taking off the cartridge, and replacing it with the same size and brand.

#3. Test the Check Valve

The dual check valve is a well-known cause of hot water flowing into the cold. Test it to see if it is not very accurate.

#4. Ensure the Water Pressure Is Right

If hot water backflows into the cold, it is primarily due to high pressure. Make sure the pressure is not too high.

If it is too high, it can affect the water temperature. To check this, make use of a pressure valve.

#5. Make Sure the Cold And Hot Water Pipes Are Not Close to Each Other 

To avoid heat radiation from hot and cold water pipes, ensure they are not close. When installing, make sure there is a gap between them.

#6. Place the Hot Water Tank In a Cold Place 

The water becomes hot in homes where the water tank is on the rooftop of the roof due to sunlight.

Therefore, ensure you place the water tanks in a position where they do not come in contact with sunlight.

#7. Install Expansion Tanks

They prevent hot water from backflow into the cold.They function better with small water heater tanks.
They remove excess pressure.
Expansion tanks control thermal expansion.

#8. Contact a Plumber

The ideal way to deal with hot water flowing into the cold is to contact your plumber. They will solve the problem if you do not know what is wrong.

Reasons Why Hot Water Is Back flowing Into Cold Supply?

Some of the reasons are as follows:

#1. High Water Pressure

The high pressure of the water causes problems. For example, it can trouble the household plumbing and make hot water backflow cold.

#2. Closeness Of Hot And Cold Water Pipes

This proximity is one of the common reasons why hot water backflows into the cold.

In addition, the temperature of the hot water pipes can affect the water in the cold pipes and make hot water come out of the cold tap.

#3. Improper Installation Of Heat Trap 

During installation, most plumbers do not install the heat traps properly. As a result, the hot water flows out of the pipes and mixes with the cold water.

#4. Heated Water Tanks

Plumbers install water tanks on rooftops in many homes. This exposure causes the water to heat up; hot water can come out of the cold tap on sunny days.

#5. If the Ventilation Ducts Are Close to Cold Water Pipes

If you install the ventilation ducts close to the cold pipes, the warm air passing through the ducts heats the water, increasing during winter.

 #6. Faulty Thermostats

Suppose the faulty thermostat will overheat the water in hot water pipes. When the water starts boiling, it flows to the cold faucet and mixes with cold water.

This faulty thermostat can make warm water come out of the tap due to the mixture.


 Flush the tank top, remove any dirt buildup and check the thermostat. There should be a balance between the hot water and the demands of your household.

If the system is faulty, call a plumber to help you fix this problem.

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