How to Find and Fix a Plumbing Crossover: DIY Repair Tips

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Find out more about common homeowners’ complaints: “not enough hot water” and “hot water runs out quickly,” the main symptoms of a plumbing crossover. How to prevent, test, and repair it successfully.

What is a plumbing crossover and how to deal with it?

Plumbing crossover can occur in any domestic hot water distribution system. Crossover leads to an unplanned flow of hot water into the cold water system or cold water into the hot water system, resulting in high energy losses, long wait times, temperature fluctuation, and discomfort.

This is why it needs to be taken care of on time and correctly.

Every home plumbing system has a hot and cold water supply divided into two main loops, but cold water can still mix with hot and vice versa without you noticing.

And that can be a problem.

The risk of getting cold water into the hot water supply system is even higher, especially in today’s modern new and remodeled homes that use mixing valves, check valves, and single-handle faucets, the primary sources of crossover.

This condition when cold water gets into the hot water system, or hot getting into the cold system, is called plumbing crossover.

Highlights of plumbing crossover symptoms

The most common causes and locations of a plumbing crossover

  • Single handle faucet
  • Mixing valve (solenoid on the washing machine)
  • Check valve
  • Hot and cold water pipes mixed up

In general, there are several reasons why the plumbing crossover problem happens. Some symptoms are easy to recognize, making repairs simple and quick, particularly for handy-people. There are also problems with no visible signs of crossover.

For the homeowners who would prefer professional service, the recommendation is to contact a local skilled plumber.

As mentioned, a single-handle faucet is often found “guilty,” for the plumbing crossover. Many homes have single-handle faucets because they are much more user-friendly, installation is simpler, and adjustment is easier. They are also more popular than two-handled faucets because they can help prevent burns because cold water is mixed in.

Mixing valves are next on the list of potential reasons. Mixing valves are widely used in plumbing to protect users from scalding temperatures. These valves are found in automatic washing machines.

Faulty check valves on recirculation systems or anywhere in a plumbing system. Check valves are used to direct water in one direction only.

How to test for a plumbing crossover

It is very easy to test for plumbing crossover. Here are the steps to take:

  • Turn OFF hot water at the water heater.
  • Turn ON all hot water faucets.
  • Wait for several minutes until the water flow stops.
  • If you see any water flowing, then you have a problem with the plumbing crossover.
  • Next, turn OFF all the faucets.
  • Open only one hot water tap at a time, then switch to the cold water side. If you see or hear water flowing, you just located where the problem is.
  • Test all other faucets, as there might be more than one crossover.

You can also test it this way:

  • Close the main shut-off valve that is supplying cold water to the water heater.
  • Open the hot water faucet only on a double-handle faucet if it is installed. If there is no double handle faucet, and you have only a single handle type, you must do the test twice and each time using a different tap. If the faucet showing crossover, it should be tested in the off position as well.
  • After some time, the water should stop running completely. If hot water is still running but at a slower rate, your shut-off valve is defective, so replace it.
  • If the water turns cold and continues to run, you have a plumbing crossover problem, where cold water is crossing over to the hot water side.
  • Next, close the service valves to the washing machine, where the hose is attached. If the water stops flowing at the hot water faucet, the mixing valve on the washing machine is a problem.
  • Check all the incoming water pipes that lead to a single-handle faucet. If you find both cold and hot water pipes cold, you have crossover.

Note: If, after testing the whole plumbing system, crossover still occurs, you might have a situation where cold and hot water pipes are directly connected.

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How to repair a plumbing crossover?

For DIY-ers, plumbing crossover is not hard to repair. Depending on the location, it requires you to replace the faucet cartridge, check valve, or mixing valve. Keep in mind that replacing the cartridge does not always solve the problem. However, buying a quality faucet, or even a cartridge, could prevent the crossover problem.

Note: Check also if the water heater dip tube operates properly. If it is broken, the cold water would, instead of reaching the bottom of the tank and mixing with hot, fill the upper part of the tank, and from there, end up in your hot water tap.

Other things to consider when troubleshooting a plumbing crossover problem

As we know, every house has cold and hot water pipes. Hot water is produced inside the tank-type water heater or tankless supplying various faucets, appliances, hot tubs, and pools.

In residential homes, water is usually heated to the maximum temperature of 140 F, and depending on the exposure time, it can produce severe burns. According to the experts, hot water temperature should be in the range from 120 to 125 F. Water is safe to use (free of bacteria) at this temperature and can do the job efficiently.

This is why following manufacturers’ instructions is important and hiring a professional plumber our best advice.


Detecting plumbing crossover can be difficult and time-consuming for homeowners with no plumbing knowledge and skills. However, it is easy to fix for experienced plumbers, so it is recommended to hire a professional. Contact an expert as soon as you notice atypical heating behavior, and avoid energy losses, high energy bills, and cold showers.

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