Regular cleaning prevents scale buildup in the heat exchanger.

Turn off gas and power before starting maintenance.

Clean the cold air intake filter and the cold water filter.

Use vinegar to descale the heat exchanger.

Flush the system thoroughly after descaling.

First things first, you need to make sure the unit is safe to work on. This means shutting off the gas and the power. To turn off the gas, find the gas line leading to the heater and turn the handle so it's perpendicular to the pipe. For the power, locate the bottom right button on the unit – it usually looks like a circle with a vertical line – and press and hold it until the power is off. You'll also want to turn off the water supply to the heater by turning the cold water inlet valve and the hot water valve so they are sideways.

Before we get too deep into things, let's take off the cover of the water heater. There are four screws holding it in place, two on top and two on the bottom. Once the cover is off, you can unplug the power cord as an extra safety step. Now, we need to clean the cold air intake filter. You'll need to loosen one screw on the front left of the intake housing. Then, remove the screw on the front of the filter itself. This will allow you to slide the filter out. You'll likely find some debris in there, maybe from construction or even some bugs. Dump this out into a bucket. It's important to clean this filter with a dry toothbrush. Getting it wet could actually cause an error code on the water heater. Once it's clean, slide it back into place, making sure the notch lines up correctly, and reinsert the screws.

Now, let's get the water out of the heater so we can clean the filters. We've already turned off the main cold and hot water inlet valves. The next set of smaller valves, usually red and blue, are the service valves. We need to remove the caps from these service valves. Hook up hoses to both of them and run them into a bucket. Then, open both service valves. This will allow the water heater to drain. Let it drain for a few minutes until no more water is coming out.

With the water drained, we can remove the cold water filter, which is located above the cold water isolation valve. You might need channel locks for this. Have a bucket ready underneath in case a little water still comes out. You'll see some residue on the filter. Clean this off with a toothbrush. Once it's clean, put it back and tighten it by hand, then give it about an eighth of a turn with the channel locks.

The last part to clean is the dirt trap. Pull out the pin, then pull the trap straight down. Make sure the o-ring is seated properly. There might be a little dirt inside the trap, so rinse it out with water and put it back.

This is where we get the heater really clean. We're going to run vinegar through the system to remove any scale. Get a five-gallon bucket and pour in two gallons of white vinegar. You'll need a small sump pump with hose threads on top. Connect the hose from the cold side of your water heater to the top of the pump. Make sure you use the cold side; the system isn't designed to run backward. Place the pump in the bucket of vinegar. Before plugging it in, make sure the return hose is pointing back into the bucket. You also need to ensure the main isolation valves are off, but the service valves are open so the vinegar can flow through the heater.

Now, plug in the sump pump. It will pump the vinegar through the cold side, up through the water heater, and out the hot side, back into the bucket. Let this run for about 45 minutes. This is the time needed to thoroughly clean the heat exchanger.

After the vinegar has done its job, we need to flush it all out. First, turn off both service valves and remove the hoses. Connect a regular garden hose to the hot side service valve. This hose should go to a drain or a laundry tub. Turn the cold water isolation valve back on and open the hot side service valve. This will push fresh water through the system, flushing out all the vinegar. Let this run until you're sure all the vinegar is gone.

Once flushed, turn off the hot side service valve, remove the garden hose, and put the caps back on the service ports. Leave the service ports in the off position. Now, turn the main water supply back on to the heater and to the rest of your house. It's time to put the cover back on the heater, turn the gas back on, and hit the power button. Your Navien tankless water heater should be ready to go!

Remember, doing this cleaning every year, or at least every other year, is like changing the oil in your car. It's a good investment to take care of your water heater, and we're here to help if you need it. Thanks for reading!