Maintenance of Navien NPE 210A Water Heater

Our water heater is installed on the back of the house behind the laundry room. It should be descaled and flushed once a year. My target date for doing this is February 1 (the water heater was installed around the beginning of February, 2021).

You will need a small pump (I purchased this 1/6 horsepower utility pump), a pair of washing machine hoses or similar, a garden hose, 2 gallons of distilled vinegar, a Philips screwdriver (preferably with a magnetized tip), and possibly a large set of slip-joint pliers.

The cold water inlet is on the righthand side of the water heater; the hot water outlet is on the lefthand side; and the recirculation inlet is in the center. Note the distinction between the cold water isolation ("D" in the user's manual) and service ("B") valves and similarly between the hot water isolation ("C") and service ("A") valves. The service valves allow for draining and flushing the water heater while the unit is isolated from the home's water supply and plumbing by closing the isolation valves.

There is no "recirculation service valve", but there is a pump drain port.

Further information and diagrams can be found in the User's Information Manual for Navien's NPE Condensing Water Heaters. The procedure below is really just combining all the maintenance into one long procedure. See also this video, which unfortunately is done with a non-recirculating model, and this video, which is less thorough but does use a recirculating model.

1. Turn off the gas valve below the water heater.

2. Turn off the water heater (power button on the water heater's control panel).

3. Disconnect (unplug) the power supply to the water heater.

4. Remove front cover. There are two screws at the bottom of the cover and two at the top. The two at the top are only accessible through the slits in the front of the top cover/lid. The hardest part of this whole job may be getting the top two screws out and then replacing them at the end.

5. Remove and clean cold air intake filter located under the top cover of the water heater.

   1. Remove screw on/next to the "handle" of the filter.

   2. If necessary, loosen screw on top of water heater which may obstruct removal of air intake filter.

   3. Slide air intake filter out and clean with a dry toothbrush. Alternatively, clean with running water and a toothbrush, but be sure the filter is dry before you replace it.

   4. Replace filter and screws.

6. Drain Water Heater and Clean Filters and Traps

   1. Close hot and cold water isolation valves.

   2. Close hot and cold service valves (these should already be closed).

   3. Close recirculation isolation valve.

   4. Optionally, drain hot water from taps throughout the house (I do not think that this is necessary).

   5. Remove caps from hot and cold water service valves and attach two washing machine hoses. Place the other ends in a 5-gallon bucket. Open both service valves to drain the water heater. (It helps to straighten the hose, keeping them running downward of course.) You may notice additional water draining into the bucket when you do the next couple of steps.

   6. Remove and clean the cold water inlet filter (black) next to the cold water inlet. On my water heater this filter is inserted into the bottom of the water at a 45 degree angle.

   7. Open/remove the (small black) pump drain plug and allow any residual water to drain from the water heater.

   8. Remove and clean the dirt trap for the condensate water clean-out. The dirt trap is white and secured with a u-shaped metal piece that you must slide out to remove the trap.

   9. Replace the condensate dirt trap. As mentioned in one of the videos above, you need to be sure that o-ring is properly seated. Don't trust your luck on this. Use a small screw driver to reach up and retrieve the o-ring and place it properly on the trap before reinserting the trap.

   10. Replace/close the pump drain plug.

   11. Remove and clean the recirculation inlet filter (black). This is exactly the same part as the cold water inlet filter, but it screws straight into the bottom of the water heater near the recirculation inlet.

   12. Replace the recirculation and cold water inlet filters.

7. Flush/Descale and Rinse Out Heat Exchanger

   1. Empty and clean a 5-gallon bucket.

   2. Put 2 gallons of distilled vinegar in bucket.

   3. Attach the free end of the hose connected to the cold water service valve to the pump and place in bucket. The pump that I purchased came with an adapter that does not change the diameter of the threads, but does change the pitch. In my experience, a washing machine hose will easily strip this adapter, so remove it first and carefully attach the washing machine hose to the pump base (it would be disastrous to strip the threads on the base itself).

   4. Place the free end of the hose connected to the hot water service valve in the bucket.

   5. Open both service valves.

   6. Run the pump for 45 minutes to an hour. The vinegar will be pumped into the cold water side of the water heater and return to the bucket from the hot water side.

   7. Disconnect the pump and allow remaining vinegar to drain from hoses into the bucket. Again, it helps to make the hoses as straight as possible.

   8. Close service both valves, remove hoses from service valves, and dispose of the vinegar while admiring the sediment that you have removed from your water heater.

   9. Replace the cap on the cold water service valve.

   10. Carefully attach a clean garden hose to the hot water service valve. I find that this is much easier using the adapter that came with my utility pump, so I put the adapter on first and then attach the hose to the adapter. (Whatever standards are in play here, the female side of the adapter matches the threads on the service valve and the male side matches the garden hose, both perfectly.) Put the other end of the hose somewhere that the water and any residual vinegar can drain without making a mess or doing any harm.

   11. Open the hot water service valve, leaving the hot water isolation valve closed. (This is important: you do not want to push the rinse solution into your house's hot water lines.)

   12. Open the cold water isolation valve, allowing cold water to flow into the cold water side of the water heater and out through the garden hose on the hot water side. Let this run for a few minutes to flush the vinegar from the unit.

   13. Close the cold water isolation valve and the hot water service valve.

   14. Detach the garden hose and replace the cap on the hot water service valve.

8. Restart Water Heater

   1. Make sure that all caps, parts, and filters have been replaced and replace the cover on the unit.

   2. Clean the outside of the unit with a damp cloth.

   3. Turn on the cold water isolation valve and the hot water service and isolation valves (the cold water service valve should also be open).

   4. Turn the gas valve back on.

   5. Reconnect (plug in) and restart the water heater.