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How to Fill a Hot Water Heater? – A Step-by-Step Guide

Fact checked by Stephen Conklin

how to fill a hot water heater

Many reasons exist as to why a homeowner would want to know how to fill a hot water heater. These include new water heater installation, low water levels due to a possible leak, and part of routine appliance maintenance (i.e., draining and flushing).

Although you can occasionally check water level, you still need to understand the steps for filling (or refilling) a hot water heating system. Worry no more if you’re unsure about this task. We’ll guide you through the steps.

Let’s start.

Table of Contents

Step-by-step to Fill a Hot Water Heater


We prepared this guide assuming two different scenarios. First, you’re filling the water heater for the first time. It could be a new installation or a water heater tank replacement.

Second, we assume you want to refill hot water heater after routine maintenance or repair.

Let’s look at the procedure.

1. Filling a newly-installed water heater

Step 1. Prepare the tank.


New water heater installation requires the appliance to be powered off (not connected to its energy source – gas or electricity). As a rule, you must fill water heater before turning on the appliance.

  • Read the water heater User Guide and check the drain valve’s location. You will find this component near the water tank’s bottom. It often has a wheel or a straight handle you can manipulate to open and close the valve.
  • Ensure the drain valve is in the OFF position. The manual should help you determine the correct “closed valve” configuration. Often, turning it clockwise will work.

Step 2. Fill the water heater.


This step involves more waiting than action. The good news is you can turn on the water heater after this step, wait several minutes, and you’re on to a refreshing warm shower.

  1. Look for a wheel or straight handle at the pipe above the water heater. Alternatively, the User Guide will direct you to the cold water shutoff valve’s location.
  2. Turn the valve handle or wheel counterclockwise (or as per User Guide instruction) to open it and allow water to flow into the hot water tank.
  3. Slowly open a few hot water fixtures to reduce pressure within the plumbing and force air out.
  4. Watch the water flow from the faucet. A steady flow (not spurting or sporadic) indicates a full hot water tank.
  5. Close the taps and turn on your water heater.

2. Refilling a water heater

Step 1. Prepare the water heater.


How to fill hot water tank units isn’t complicated. The procedure is the same as what you would do when draining and flushing the tank, except the focus is on refilling it with water.

  1. Unplug the heating appliance or disconnect it at the breaker panel. Twist the gas supply valve to close it and shut off the fuel flow.
  2. Wait several hours to cool the water.
  3. Connect a flexible pipe or garden hose to the water heater’s drain port.
  4. Place the hose’s other end over a floor drain or run it outside the house.
  5. Turn the water inlet valve handle or wheel clockwise to prevent water from entering the tank.

Step 2. Drain the water.


  1. Locate the water heater’s T&P relief valve near the water tank’s top. Twist the valve to open it.
  2. Open a nearby hot water fixture to release pressure and initiate the draining process.
  3. Rotate the hot water tank’s drain valve clockwise to open it.
  4. Observe the water flow and check for sediments and other impurities.
  5. Close the drain and T&P relief valves after draining the water.
  6. Detach the hose.

Step 3. Refill the hot water tank.


  1. Rotate the water inlet valve handle or wheel counterclockwise to refill the hot water tank.
  2. Observe the water flowing from an open hot water fixture.
  3. Close the hot water tap once the water flow steadies (doesn’t spurt), indicating a full tank.
  4. Reconnect the water-heating appliance to its power supply (i.e., at the electrical panel or the gas supply valve).
  5. That’s how you fill up a water heater.

Here’s a video on how to refill a water heater.


How to fill a hot water heater isn’t rocket science. In most cases, you don’t even need materials. However, we recommend reading the User Guide to help you perform the steps specific to your water heater type, brand, and model.

Our simplified instructions should help you fill a newly installed heating appliance with water or make you feel more confident about draining and flushing the tank. You can try these steps on your next maintenance schedule.

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