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heating and AC, plumbing & electric 479.900.0784
September 16, 2022

Here's Why Your Tankless Water Heater Takes a While to Heat Up

If you’re reading this, it’s likely that you have been puzzled by your tankless water heater’s slow pace. You’ve made the upgrade to a tankless system, expecting quick, efficient hot water on demand, but your reality is a bit different – your hot water is taking its sweet time. Fret not! In this comprehensive guide, we will dive deep into the reasons why your tankless water heater might be acting this way and what you can do about it.

What is a Tankless Water Heater?

Before we plunge into the nitty-gritty, let’s establish what a tankless water heater is. Unlike traditional water heaters, which store and heat water in a tank, tankless water heaters (also known as demand-type or instantaneous water heaters) provide hot water only as it is needed. They are designed to heat water directly without the use of a storage tank, thereby avoiding the standby energy losses associated with storage water heaters. This means they can be more energy efficient, cost-effective, and provide the convenience of endless hot water.

How a Tankless Water Heater Works

Understanding how a tankless water heater works is key to comprehending why it might take longer to heat up water. Here’s a simplified explanation:

  • 1) When a hot water tap is turned on, cold water travels through a pipe into the unit.
  • 2) Either a gas burner or an electric element heats the water.
  • 3) As a result, tankless water heaters deliver a constant supply of hot water. You don’t need to wait for a storage tank to fill up with enough hot water.

Reasons for Slow Heating

Although tankless water heaters are designed to provide hot water on demand, there are several reasons why they might take a while to heat up. These include:

Size and Capacity of the Unit

The capacity of your water heater to deliver hot water efficiently depends on its size and the demand placed upon it. A smaller unit might struggle to deliver hot water quickly, especially if you have multiple hot water applications running simultaneously.

Distance Between the Heater and Tap

The longer the distance between your water heater and the tap, the longer it takes for the hot water to reach the tap. This delay is due to the time it takes for the hot water to travel through the pipes.

Mineral Buildup

Over time, minerals present in water, particularly hard water, can accumulate inside your tankless water heater, forming scale buildup. This buildup can hamper the efficiency of your water heater, causing it to take longer to heat the water.

Low Gas Pressure

If your tankless water heater is gas-powered and the gas pressure is too low, your heater may struggle to reach the desired temperature quickly.

Potential Fixes and Solutions

Now that we’ve understood some reasons behind the delay, let’s dive into potential solutions:

Upgrade Your Water Heater

If your water heater is not able to meet the hot water demand of your home, you might need to consider upgrading to a larger unit. Consult with a professional plumber to determine the appropriate size and capacity for your needs.

Install a Recirculation Pump

A recirculation pump can help speed up the delivery of hot water by circulating hot water from your heater to your taps and back. This ensures that hot water is always close to the point of use, minimizing the wait time.

Regular Maintenance and Descaling

Regular maintenance, including descaling, can help keep your water heater in optimal condition, preventing scale buildup from affecting its performance. Descaling involves flushing out the mineral deposits from the heater using a descaling solution.

Adjust Gas Pressure

If the gas pressure is low, adjusting it to the appropriate level might help your water heater operate more efficiently. However, this should only be done by a certified technician to avoid any potential hazards.

Preventive Measures

Prevention is always better than cure. Here are a few measures to prevent slow heating:

  • Regular maintenance: Maintain your water heater regularly to ensure it works efficiently. This should include descaling, especially if you live in a region with hard water.
  • Install a water softener: If hard water is an issue in your area, consider installing a water softener to reduce mineral buildup in your tankless water heater.
  • Optimal installation: Ensure that your water heater is installed as close as possible to the point of use to reduce the distance hot water has to travel.

Frequently Asked Questions

Q1: How often should I descale my tankless water heater?
A1: Generally, it’s recommended to descale your tankless water heater once a year. However, if you have hard water, you might need to do it more frequently.

Q2: Can I adjust the gas pressure of my tankless water heater myself?
A2: It’s highly recommended to let a certified technician adjust the gas pressure. Incorrectly doing so could lead to potential hazards.

Q3: How can I tell if my tankless water heater is the right size?
A3: If you frequently run out of hot water or if your hot water takes a long time to heat up, your unit might be too small. Consult a professional to help determine the right size for your needs.


While tankless water heaters are designed for efficiency and on-demand hot water, they can sometimes take a bit longer to deliver the hot water we desire. The reasons can range from the size and capacity of the heater, the distance between the heater and tap, to mineral buildup and low gas pressure.

By understanding the reasons and potential fixes, you can take steps to improve the situation. Regular maintenance, appropriate installation, and taking preventive measures can go a long way in ensuring that your tankless water heater provides you with the hot water you need, when you need it.

Should you need professional assistance, the experienced team at Paschal Air, Plumbing & Electric is here to help. We have the knowledge and expertise to handle all your tankless water heater needs. Get in touch with us today!