How To Reset A Tankless Water Heater [4 Easy Steps]

Tankless water heaters are designed to provide an endless flow of hot water. But if there is a power outage or some other event that causes the unit to lose energy, how do you get it back up and running? And what to do if your tankless water heater is not heating up?

You may have heard that tankless units don’t have a pilot light like your standard water heater. 

The good news is that most tankless water heaters can be reset in a minute or two. The catch is that not every model has a reset button. Many reset when you switch the unit off and on at its On/Off button or its power supply. These steps show how to reset your tankless water heater safely, and your owner’s manual has the final say for your model.

How to reset a tankless water heater: 4 quick steps

Step 1: Check your manual for how your model resets

How a tankless water heater resets depends on the make and model. Some have an On/Off button on the unit or on a remote controller, some reset when you switch the power off and on, and some have no reset button at all. Rinnai, for example, says error codes vary by product and tells owners to contact Rinnai or their installer. Check your owner’s manual to confirm what yours does.

If you can’t find it after a few minutes of searching, call the customer service number of your water heater provider.

Step 2: Switch the unit off and back on

To start up the heating process again, turn the unit off with its On/Off button or its power switch, give it a moment, and turn it back on. Rinnai’s service documents describe pressing On/Off twice to clear one code and switching the power off and on to clear others, so follow your manual for the exact steps.

Open a hot tap and see whether the unit fires up. If it is an electric tankless model, do not switch the power back on until the pipes are full of water. EcoSmart’s manual says to run a hot faucet until the flow is steady and free of air before the breaker goes on, because power with air in the heater can permanently damage the heating elements.

Afterward, if there’s still no power going to the unit, call a professional because your tankless water heater may have a larger issue.

Step 3: Check the temperature setting

Look at the temperature setting on the unit or its controller. Do not turn it to the maximum. Keep it at 120°F or lower. The U.S. Environmental Protection Agency recommends 120°F to prevent scalding, according to the Department of Energy’s Building America Solution Center, and Rinnai’s manual warns that water above 125°F can cause severe burns, in as little as 3 seconds at 140°F.

Then open a hot tap and give the unit a few seconds to light. If the water stays cold, do not keep raising the setting. Check the power and gas supply instead.

If it still will not heat, move on to Step 4.

Step 4: Check for a power outage in the house

Sometimes the heater is fine and the power is the problem. Even a gas tankless heater needs electricity, because Rinnai’s units run on 120 volts, so a power cut stops it too.

Some external reason, such as a downed power line on the street outside your house, or an issue with how well your electricity is supplied, has made you lose energy in your entire home rather than just your tankless water heater.

So how do you fix this? Check the breaker for the water heater.

If the lights are on but the heater is dead, look in the electrical panel for a breaker that has tripped to the middle or off position. An electric tankless heater may use more than one breaker, and they are labeled for the water heater.

Switch only the water heater’s breaker fully off and then on, once. Do not keep resetting a breaker that trips again: that points to a wiring or heater fault, so hire a licensed electrician. Never open the unit’s cover with the power on.

Afterward, open a hot tap and wait for the unit to fire up. On a gas model, also make sure the gas valve is open. If you smell gas, leave the building and call your gas supplier from outside: Rinnai’s manual says not to touch any electrical switch or use a phone in the building. For gas or 240-volt work, hire a licensed plumber or electrician.

Still Not Receiving Power From Your Tankless System?

If you’re still not receiving power from your tankless system despite following these steps exactly, call a professional because this likely isn’t an isolated incident but part of a larger problem.

I hope that was helpful!

Although this blog post was specifically about how to reset a tankless water heater, these steps are for tankless units only. A tank water heater resets differently, so check its owner’s manual or see our guide to the most common water heater problems. Check out some other useful tips for home appliance maintenance!