Introduction: How to Flush a Tankless Water Heater and Clean the Air Intake Filter

Tankless water heaters will build up calcium and debris on the elements and the filters inside the machine. It's important to perform a flush with food-grade, white vinegar at least once every 12 to 18 months. Performing this simple maintenance will improve the efficiency and life of your water heater. It's also a good time to clean the air filter inside the tankless water heater while you're doing the flushing.

This instructable will show you have to perform a tankless water heater flush on a Navien brand device, but it can be applied to any tankless water heater as long as you can locate the corresponding components on your machine.

Step 1: Gather Your Materials

For this task you're going to need:

- Five (5) gallon bucket
- Two (2) stainless steel washing machine hoses
- A submersible pump,
- Four (4) gallons of white, food-grade vinegar. The same you'd buy at any grocery store.

I decided to purchase mine through amazon. This kit was is about $150 at the time.

Step 2: Locate the Shutoff Valves

You should notice that there are color coded handles underneath your tankless water heater. These levers will shut off the water and gas to you tankless water heater. If the levers are in-line with the pipe that means it's ON and if it's perpenticular that means it's off. Make sure to turn them all perpenticular to the pipes. This way you will shut off the gas (yellow handle on the right side attached to the silver pipes), Central yellow handle, the cold water intake (blue), and the hot water outflow (red).

At this point you can also unplug your unit from the wall socket.

Step 3: Unscrew the Cold Water Service Valve

Just above the red and blue levers is a service valve. Now that you have turned the levers perpendicular to the pipe and shut off the water to the tankless water heater, you can open the service valve. BUT before you do, get your materials ready.

Note: There is an external pump that's attached to the wall near the floor. It's electronic components are exposed through the vents at the top of the device. You should try to avoid getting any water on this device so as not to short circuit it.

Make sure to have your bucket ready to catch the water that comes out. It won't shoot out, but rather it will trickle out. It's not much, but you still don't want it on your garage floor. One thing you can do is get one of the hoses that comes with the kit and have it ready. Place one end into the bucket so when you unscrew the service valve cap you can try to quickly plug the hose into the opening and redirect some of the water into the bucket.

Once you complete the cold water side you can try the hot water side. I think our water heater is set to only 120 degrees Fahrenheit. Be very careful not to burn yourself. Ideally you haven't been taking hot showers, running the dishwasher, and washing machine right before doing this because the water that comes out of the hot water service valve may be really hot. Depending on how long your tankless water heater has sat idle will determine how hot the water is coming out of the service valve on the hot side. You may want to unscrew the service valve slowly in case the water is hot so you don't burn yourself.

What I did is had my bucket and hose ready just like for the cold water valve and I slowly unscrewed the hot water service valve until it just started to leak water. I could then feel that the water wasn't hot, just warm, so I finished unscrewing the service valve, plugged in the hose and let the water drain into the bucket.

Note: The hot water side comes out much quicker and in a larger quantity than the cold water side.

Step 4: Setup Your Vinegar and Pump

By now if you used the hoses to attach to the service valves in the previous step they'll be ready to go for this next step.

Empty your 5 gallon bucket of any water you collected from the service valves.

Fill the bucket with 4 gallons of food-grade, white vinegar. I bought a generic brand from Safeway and the total was $16 for 4 gallons.

Attach the hose going into the cold water (blue) service valve into the top of the sump pump. Make sure all connections are on tightly. Do not plug in the pump yet.

Place the pump into the vinegar before plugging it into the wall. There is no on or off switch so it'll turn on as soon as you plug it into the wall socket. Again, before you plug in the sump pump into the power outlet make sure the hose going into the hot water service valve is attached securely and that the other end is placed into the bucket with the sump pump. It does not need to be screwed into the pump, just loosely placed in the vinegar bucket.

Now that the hoses are attached and the pump submerged in the vinegar, you're ready to begin.

Go ahead and plug in the pump into the power outlet. It will start to circulate the vinegar in through the cold water service valve (blue) and out hot water service valve (red) and into the same vinegar bucket.

You're going to leave it like this for at least 60 - 90 minutes. The manual says 45 min, but I figured it's been so long just run it longer.

Step 5: Cleaning the Air Intake Filter

While your vinegar is circulating, you should also clean out the air intake filter. If you've been noticing an error message on your display that reads "027". That means you need to clean the air intake filter.

The air intake filter is located inside the tankless water heater. Don't worry it's not hard to get to at all, but you have to first remove the tankless water heater face plate. It is held together with 4 screws. 2 on top and 2 on bottom.

To remove the face plate you have to first unscrew all the screws and then lift upwards to unhook the top of the face plate from the top of the tankless water heater frame. This will expose the inside of the water heater.

Next located the single screw holding the air intake filter in place. You can see in the photos I'm pointing at the air intake filter.

To remove the air filter once you've unscrewed the one screw, first pull slightly towards you and then slide the whole thing to the left and angle it slightly so it will slide over the motor. You can see how in the series of photos I took.

Then I just walked over to my water spout outside my garage and turned it on full blast and rinsed the heck out of the filter. Then I used paper towels to dry it as best I could and reinstalled the filter the same way I took it out.

Replace the tankless water heater face plate and let the pump continue to run for the remainder of the 60-90 minutes. Don't plug the tankless water heater into the outlet until you're done running the flush process.

Step 6: Rinse Your Tanless Water Heater After the Vinegar Treatment

Now that the pump has circulated the vinegar for 60-90 minutes you're ready to rinse the vinegar out of the tankless water heater.

Unplug the pump from the wall outlet and lift out the sump pump. Allow it to drain into vinegar bucket and place it aside. I decided to dump the vinegar into the toilet rather than on the grass or plants to avoid damaging the foliage.

Now that you have an empty bucket, place the bucket back under the tankless water heater. Unscrew the hose from the cold water (blue) side only. Replace the service valve cap and screw it on. Leave the hot water hose attached.

Next open the lever that controls the cold water inflow and allow about 4-5 gallons of water to flow through the tankless water heater and out the hot water hose into the bucket. Make sure to then close the cold water valve.

Once that is complete you need to check the water filters. In the photo I'm pointing to both of them. You can just use your fingers to unscrew these. There maybe some water that comes out of them which is why you should have the hose that you used for the cold water (blue) side handy so you can redirect water back into the bucket.

After you remove the filters, make sure to inspect it for debris. Thoroughly rinse the filters with water and screw them back in.

Step 7: Reattach Everything and Turn It on - Moment of Truth

Now that your tankless water heater has been thoroughly descaled and your air intake filter has been cleaned, it's time to reassemble everything.

Make sure to screw on all service caps tightly before opening any valves.

Once you're sure everything is capped off tightly you can start opening valves. I would first start with the cold water valve. You'll hear water rushing into your system. Next open the hot water valve. Then the gas and central circulation valve (yellow). Now plug in the tankless water heater.

Once the display powers on the machine cycles you may notice certain icons on the display.

That's it. Hopefully it goes smoothly for you as it did for me. Let me know if you have questions of I need to clairify anything.