DIY Maintenance Guide for Rheem Tankless Water Heaters

Last Updated on: 11th December 2023, 07:49 pm

Some folks can get a bit intimidated about maintaining their tankless water heaters. They worry they might mess something up or flood their entire house. But fear not, my friends! With some know-how and common sense, anyone can keep their tankless water heater chugging like a well-oiled machine.

So stick around if you’re keen to learn a thing or two about keeping your Rheem tankless water heater in tip-top shape! I’ve got some DIY maintenance tips that are so easy. Even a monkey wrench could do them. Let’s get crackin’!

Table of Contents

How To Service A Rheem Tankless Water Heater

Flushing With A Flush Kit

Here are some step-by-step instructions for flushing it with a flush kit:

Materials Needed:

  • Rheem Tankless Water Heater Flush Kit (available here)
  • A bucket or drain pan
  • A small submersible pump (the kit I linked above has a good pump that works well for this).
  • A large jug of vinegar or two.

Cleaning And Descaling With A Cleaning Kit Instructions

Please turn off the power supply or switch off the circuit breaker by unplugging it.

Shut off both the hot and cold water valves.

Pour the vinegar into your bucket. You are going to need a lot – around 4 gallons.

Connect your flush kit host to the pump’s inlet and place the pump inside the bucket of vinegar.

Attach the hose connected to the pump to the service cold water valve at the bottom of the tankless water heater.

Connect the other hose to the hot side of the water heater and drop the other end into the bucket.

Open the service valve and allow all the water in the tankless water heater to drain through the garden hose into the bucket.

Turn on the pump to circulate water through the heater and the flush kit.

Allow the pump to run for at least 60 minutes to ensure all the sediment and mineral buildup is flushed out of the heater.

Turn off the pump and close the service valve.

Disconnect the flush kit from the service valve and remove the hose from the service valve.

Open the cold water supply valve and allow water to flow into the tankless water heater and out the hose connected to the hot side.

Let it run for a minute or so to flush out the vinegar.

Turn the cold water back on.

Please turn the power supply on your Rheem tankless water heater by plugging it back in or switching on the circuit breaker.

The flushing frequency depends on various factors, such as the hardness of your water, the amount of usage, and the manufacturer’s recommendations. 

Flustering your tankless water heater at least once a year is recommended to remove any mineral buildup that can reduce its efficiency and lifespan. However, if you have hard water or high usage, you may need to flush it more frequently, such as every six months.

Freeze Protection And Winterizing

Freeze protection and winterizing are critical maintenance tasks for Rheem tankless water heaters in cold climates where temperatures drop below freezing. Without proper winterization, the water inside the unit and pipes can freeze and cause significant damage to the system.

The good news is that as long as the unit has power, it will protect itself from freezing with a heating element inside. Most units have cold ratings showing how cold it can get before it risks freezing. For example, mine is good to -4 degrees F.

The problem arises in the pipes that lead into the unit.

But what if the power goes out in the winter?

Get a generator or battery-powered unit to keep your heat tape on and get some temporary power to your water heater.


Proper maintenance and winterization are crucial for Rheem tankless water heaters’ efficient and safe operation, especially in colder climates where temperatures drop below freezing. Flushing the system at least once a year and installing a freeze protection kit can help prevent sediment buildup and freezing.

It’s also essential to insulate the unit and pipes and consider installing a backup power supply to keep the freeze protection kit functioning during a power outage. By taking these steps, you can ensure that it stays in good working condition and provides reliable hot water whenever needed. There is nothing worse than having to troubleshoot tankless hot water heater problems.

If you have any questions or concerns about error codes, maintaining or winterizing your tankless water heater, consult a qualified plumber for advice.