How to Set the Temperature on a Tankless Water Heater

It is disconcerting to watch utility bills spiral out of control. That’s probably the main reason why some decide to go tankless with their water heater. Why not? It is environmentally-friendly, highly efficient, and will help you save in the long run despite the high upfront cost. Saving on fuel usage will also lower your carbon footprint. But making sure you get the optimal temperature setting can be tricky.

set the temperature on a tankless water heater

Tankless water heaters normally have a default temp setting of 120°F and will not go any hotter than that. It is a safety measure that heater companies devised to prevent accidental scalding, especially if you have children.

It is also one way of saving energy to help you cut off on fuel consumption. If you need to crank it up, a few tinkers on the control panel will help you do that. So in this post, we provide the steps on how to set the temperature on a tankless water heater.

Types of Tankless Water Heaters

There are two main systems of a tankless water heater. First is the basic whole-house that heats water in a central heater and delivers it upon opening the faucet. As the name suggests, it caters to the whole household and is best for low daily water consumption. Its disadvantage is the standby heat loss or heat wasted going from the tank to the tap. It defeats the energy-efficiency feature of a tankless water heater.

The second one is POU or point-of-use devices. It functions by heating water very near the water outlet like the faucet, bathtub, or showerhead. Installation of multiple POU devices allows individual control of temperature from these outlets or exit points.

They are ideal for homes with water consumption that is higher than 40 gallons a day. However, they are prone to producing a limited water supply when water outlets are used simultaneously.

Related: Rheem Water Heater – Ultimate Troubleshooting Guide

Normal Setting Temperature on a Tankless Water Heater

The 120°F default setting is the normal temp setting for a tankless water heater. It is already good enough for meeting various household uses like showering or kitchen usage. The setting will also give you just the right flow of water on your outlet. The tankless unit may restrict the water flow to reach a higher temperature setting. In other words, the higher the thermostat, the lower your water pressure.

But some people are not here just for the 120°F. So, if you need a temperature that is hotter than the default, here is what you need to do. This step-by-step guide directs you to set your desired tankless water heater temperature setting. The display on the LED panel may vary from brand to brand, but these are the general functions that most units have:

  • Turn the on/off thermostat dial on the control panel of your tank.
  • Press the Priority Function until it lights up.
  • Press and hold the Arrow Up button until the display temperature changes from 120°F to 140°F. The figure on the screen will start blinking.
  • Press the Up and Down Arrow together until it stops blinking.
  • Set the figure to your desired temperature using the Up or Down arrow. Some models increase or decrease the temp by a 5-degree increment. Other units are customizable by degree.
  • Some water heaters like the Rinnai Tankless Water Heater have a lock function. You can enable it by pressing together the Priority and Arrow Up Button until the LOC appears on-screen.
  • To reset to the default setting, you can press the Priority and Arrow Down button and repeat step 4.


Can you adjust the thermostat beyond the default setting even if it seems locked?

What happens if you cannot crank up the heater any higher than the default setting? The solution for this lies in the circuitry inside the tank. However, you may need to call the help of a professional who can set it for you.

For the POU device, adjusting the control panel’s thermostat will let you individually adjust the remote panel by the water outlet. If you are using the whole-house system, be wary about the risk of scalding. Make sure that you set the right temp especially if you are using it on children.

Is 140 degrees just right or too hot for a tankless water heater?

While the standard tankless water heater temperature setting is 120°F for household use, 140°F is also a safe bet. Some people are accustomed to showering at this temperature level if you want a bit of a temperature rise.

It is beneficial for preventing bacterial growth and for keeping the body energized. It is manageable enough, but certainly not for children younger than four years old. And even if your thermostat allows, never go beyond the 140°F thermostat setting. It is also important to understand that the 140°F is mostly used for commercial purposes only.

Why does it take longer to get hot water with a tankless water heater?

On-demand hot water does not necessarily mean instant hot water as soon as you turn on the faucet. Even if you have a POU device, it will still take a few seconds for your hot water to be ready. The water flow, the distance of the heater from the pipe, and the outside temperature still dictate the water’s waiting time.

Why won’t my tankless water heater get any hotter?

The outdoor temperature in your area may affect the performance of your water heater. Sometimes, sediment build-up or the hardness of the water also prevents the water from heating up instantly. If you are using a lot of outlets simultaneously, it will also impact the temperature of the water.


temperature adjuster of water heater

If you want a hot water heater, the tankless option is an innovative and highly sustainable item for a household water heating system as opposed to a tank water heater. It produces hot water on demand making it highly efficient and cost-saving.

Tankless water heaters are advantageous in many ways. However, one of its downsides is that it is prone to producing inconsistent water temperatures. Sizing up your tankless heater to your average consumption is the solution for maintaining a hot water supply. Knowing how to set the temperature on a tankless water heater may also help solve the dilemma.

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