How to Drain a Water Heater (Updated Step by Step for Tank and Tankless) 

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In many homes, the water heater is the most frequently replaced major appliance so learn how to drain a water heater and extend its lifespan. Without proper maintenance, it lasts as little as six years. 

In this blog from Cincinnati’s Apollo Home, we’ll review why you should drain a water heater, how to drain water heaters, how to drain a tankless water heater and even why maybe you shouldn’t drain a water heater. 

Why Should I Drain My Water Heater?

Draining a water heater annually also improves performance and reduces operating costs. Why? Because all municipal water supplies contain a level of naturally-occurring dissolved minerals known as “hardness.” 

As hard water heats, minerals gradually accumulate in the bottom of the water heater tank. If the tank isn’t regularly drained, this layer of sediment solidifies. This mass forms a permanent barrier and the heat from the burner flame takes longer to reach the water in the tank. 

Burner cycles increase and consume more gas until the tank finally becomes unusable and must be replaced. 

How to Drain a Tank Water Heater

Draining the sediment from a tank water heater once a year is an easy DIY task:

  1. Power off. If the heater is natural gas-fueled, turn water heater gas valve to the “off” position. If it’s an electric water heater, turn off the power to the heater at the switch or circuit breaker.
  2. Shut the cold water inlet valve on top of the heater. Open up a hot water tap in the house somewhere close to the water heater.
  3. Connect a garden hose to the drain outlet located near the bottom of the heater. Route the other end of the hose outdoors to an appropriate discharge location.
  4. Open the drain valve and allow the tank to drain.
  5. After the tank is empty, open the cold water inlet valve and flush the tank for several minutes until water emerging from the hose appears clean.
  6. Close the drain valve and the hot water tap you opened earlier. Disconnect the garden hose.
  7. Allow a few minutes for the tank to refill completely with water. 
  8. Following manufacturer’s instructions, relight the pilot, then turn the gas valve to “on.” For an electric water heater, restore electricity at the power switch or circuit breaker.

How to Flush a Tankless Water Heater

Many homeowners don’t consider draining a tankless water heater necessary because it doesn’t store water. It’s true tankless models heat water on demand but water passes through them. The same minerals build up and erode the surface of the tank’s heating chamber. 

Because tankless models can last as long as 20 years, it’s good to know how to drain a water heater to get the most from your investment.

Steps to Drain a Tankless Water Heater

  1. Turn off the tankless water heater power source. 
    1. For gas, shut off the main gas valve. For electric, turn off the dedicated circuit breaker.
  2. Close and turn off the water valves connected to your tankless water heater. There should be three. 
    1. There should be a) a blue cold water valve, b) a red hot water valve and c) the main valve which runs water into your house. 
    2. This prevents hot water from coming out during the task and prevents cold water from moving into the water heater.
  3. On each of the cold and hot water valves you’ll see purge valves. Remove the purge port valve caps. 
    1. Identify purge valves by their small “T-shaped” handles
    2. This step relieves any pressure inside the valves and prevents burns from hot water spraying out.
    3. CAUTION: make sure the hot water valve is completely shut off for safety. There is often pressure released when removing purge port valve caps.
    4. Be sure caps and rubber washer sealing discs remain in place. Without these washers, the valves won’t work right. 
  4. Attach the hosing lines to each water valve.
    1. Your tankless water heater may have included hosing lines from the manufacturer. If not, these are available from hardware or home repair stores. Just be sure they’re long enough to connect the water heater and your bucket.
    2. Some manufacturers have extra or specific instructions for this step. Consult your owner’s manual if necessary. 
    3. Sometimes this step requires the water from the heater to drain using the sump pump. Again, consult your manual if you’re committed to DIY.
  5. Twist purge port valves perpendicularly to the position of the hot and cold valves. This opens the purge port valves.
  6. Use undiluted white vinegar to clean your tankless water heater. 
    1. Avoid the temptation to use chemical cleaners because your water heater provides drinking and bathing water. Chemical cleaners, therefore, may be harmful to your health. 
    2. We recommend using 2.5 gallons of undiluted white vinegar. Cider vinegar is not a good substitute, it will stain the tank. Also, use fresh vinegar. Don’t reuse from a previous flush.
  7. Flush and drain according to your water heater’s manufacturer. This may take up to 45 minutes.
  8. After flushing completes, close the purge port valves by twisting the “T-shaped” handles.
  9. Disconnect the hosing lines from each water valve and remove.
  10. Replace the purge port valve caps on the valves. Be sure to avoid breaking the rubber sealing discs inside the caps when you completely tighten the caps.
  11. Restart the water heater. Again, refer to the manual for precise directions to do this safely.
    1. This procedure often requires you to rotate and open the hot and cold water valves to a parallel setting to the main water valve to the house.
  12. Slowly turn on the hot water tap in a nearby sink. This allows the water to pass through the pipe. 
    1. This may take two to three minutes for the water to run without air in the mix.

What if the Water Heater Won’t Drain?

If the water won’t drain from the tank or comes out in a trickle, you probably have a clog. We recommend calling a licensed plumber from Apollo Home to deal with it. 

When You Shouldn’t Drain a Water Heater

This may sound contrary, but sometimes it’s best not to drain your water heater. Why? Because if it hasn’t been drained in several years, the sediment slightly displaces the water. This creates hot spots on the tank’s bottom. 

The flame overheats the tank in these areas and over time, break down the materials. The breakdowns create a tiny hole. The sediment, ironically, plugs the hole. 

If, however, you flush your water heater after years of sediment buildup, a leak within two to three days is highly likely. 

Have Better Things to Do Than Drain A Water Heater? Call Apollo Home

We’re eager to share our plumbing expertise. We’ve learned a lot in our more than 100 years and gladly use it to help you. 

Click Here to Schedule a Plumbing Service, Repair or Installation

Our friendly plumbers are licensed, insured, and background-checked for your peace of mind. They receive ongoing certified training to repair or service any brand of water heater. 

Apollo Home plumbers also handle issues with clogged toilets and sinks, garbage disposals, slow drains, leaky pipes and sewer lines. 

We travel throughout Cincinnati, Ohio and northern Kentucky to serve homeowners. Need emergency plumbing repair? If you have a water heater leak or any plumbing emergency, call us 7 Days a week.

Tired of your old water heater? If you’re curious about a new tank or tankless water heater, let us know! We’re happy to provide a free estimate for water heater installation

Updated August, 2019

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