Why is Hot Water Coming Out of the Cold Tap? (2023)


At John C. Flood, we understand that it can be quite puzzling and frustrating when you turn on the cold tap expecting chilly water, only to be met with warm water instead. This unexpected occurrence can leave homeowners wondering about the possible causes and solutions. In this comprehensive article, we will delve into the reasons behind hot water coming out of the cold tap and provide you with valuable insights to help you address and resolve this issue effectively.

  1. Location of Pipes

One of the common culprits behind warm water flowing from the cold tap is the positioning of the hot and cold-water pipes. If these pipes run parallel to each other up to the sink faucet, it can result in temperature transfer. This means that the hot water may feel colder, while the cold water may feel hotter. Over time, the hot water pipe can heat the cold water pipe, leading to warm water coming out of the cold tap. This issue is prevalent in many households.

  1. High Water Pressure

While high water pressure can be desirable for certain tasks, excessive pressure can cause problems throughout your home's plumbing system. In some cases, it can even lead to hot water flowing from the cold tap. The increased pressure can disrupt the balance between hot and cold water, resulting in warm water coming out of the cold side. It is crucial to ensure that your water pressure is properly regulated to avoid such issues.

  1. Faulty Thermostats

Often, temperature issues in your home can be attributed to faulty thermostats. In the case of hot water coming from the cold tap, it is possible that the thermostat on your immersion heater is malfunctioning. A broken thermostat may not regulate the water temperature adequately, causing it to overheat and mix with the cold water supply. To rectify this problem, it is advisable to consult a professional plumber who can diagnose and repair the faulty thermostat effectively.

  1. Copper Heating Effect

Copper piping, known for its durability and longevity, has the advantage of being highly heat-conductive. While this characteristic is beneficial in many ways, it can also contribute to warm water coming out of the cold tap. When hot water flows through copper pipes, it can heat up the entire fixture, resulting in the warming of any cold water passing through subsequently. Although this phenomenon is normal, it is important to ensure that the copper pipes have sufficient time to cool down to avoid any discomfort.

  1. Water Expansion Tank Valves

If your home has a water expansion tank, it relies on a one-way valve to lower pressure on the water meter. However, if this valve is broken, it can cause hot water to flow into the cold water tap. This issue is a common cause of warm water coming out of the cold side. To resolve this problem, the broken valve will likely need to be replaced by a professional plumber, ensuring the restoration of cold water temperature.

  1. Poor Heat Trap Installation

When it comes to plumbing installations, it is vital to engage the services of a trusted professional. Improper installations, such as a poorly installed heat trap, can lead to various issues, including the mixing of warm and cold water. During the installation process, the heat trap must be correctly placed in the water heating inlet. Failure to do so can result in warm water infiltrating the cold water lines, causing discomfort and inconvenience. If you suspect that a bad heat trap installation is the cause of hot water coming from the cold tap, it is advisable to seek professional assistance promptly.

  1. Faucet Cartridge Issues

Modern sink faucets are equipped with cartridges that direct water flow. If your faucet cartridge is faulty or broken, it can cause water to be directed incorrectly or draw solely from the hot water pipe. This malfunction can lead to hot water flowing from the cold tap. To address this issue, the solution involves replacing the damaged cartridge with a new one. It is essential to choose a cartridge of the same size and brand for optimal compatibility.

How to Fix Hot Water Coming From Cold Tap

Before attempting any DIY plumbing repairs, it is crucial to recognize that your home's plumbing system is complex and best handled by professionals. Nonetheless, depending on the source of the problem, there are several potential solutions for fixing hot water coming from the cold tap. Here are four simple steps to guide you:

  1. Turn Off Water Supply

Prior to commencing any repairs, it is imperative to shut off the water supply. This precautionary measure ensures that you can work on the plumbing without triggering any water leaks. Ideally, you should turn off the water valve for the section of the house experiencing the temperature issue. Allow the water to drain out of the tap to eliminate any excess water in the pipes.

  1. Check Pipe Temperature

Once the pipes are free of water, assess the temperature by placing your hand against the piping under the sink. Focus on the cold water supply line and determine whether it feels hot, cold, warm, or room temperature. The hotter the cold water pipe, the more serious the issue may be. If the source of the problem is near the sink, you may be able to resolve it with a simple repair. However, if the problem persists elsewhere, it is advisable to seek professional assistance.

  1. Replace the Faucet Cartridge

In many cases, a faulty faucet cartridge can be the cause of hot water coming from the cold tap. To rectify this, unscrew the faucet, remove the damaged cartridge, and replace it with a new one. Ensure that the replacement cartridge is of the same size and brand as the previous one for optimal compatibility.

  1. Test Your Faucet

After replacing the faucet cartridge, reassemble the faucet and turn the water supply back on. Allow the water to run for a few minutes and observe whether the cold water is now cold or still warm. If the issue persists, it is likely a more complex problem that requires professional attention. In such cases, it is recommended to contact a trusted plumber to assist you in resolving the issue effectively.


In conclusion, encountering hot water flowing from the cold tap can be an unexpected and perplexing situation. However, understanding the potential causes and implementing appropriate solutions can help you address and resolve the issue promptly. We hope that this comprehensive article has provided you with valuable insights and guidance on how to tackle the problem effectively. Should you require professional assistance or have further plumbing concerns, do not hesitate to reach out to John C. Flood at 703-214-5611. Our experienced team is ready to provide the necessary support and expertise for all your plumbing needs.

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