Flow Sensor Tankless Water Heater

This was an exact fit for a NAVIEN NP-240A unit. I uploaded a photo of the interior unit and highlighted the area where this installs. I would say this is a intermediate install so if you’re slightly mechanical, it’s not too difficult! The part was genuine, and the functionality was restored on my unit! I shared some photos of my unit to help other people in this situation. Have a great day!

We were experiencing intermittent cold water from our 9 year old Navien NR–240A tankless hot water heater. We even have the recirculation loop to keep hot water in the pipes every 30 minutes. In recent months, every time I went to do dishes at the kitchen sink, I would have to wait for an extremely long time to get hot water. Sometimes I would start with hot water and then it would run cold. If I turned on the shower too, I could force more demand on the water heater and get hot water sooner. I did some searching for answers on YouTube and found that these symptoms are textbook and common at about 9 years. This was a very easy DIY repair. Just a few simple tools, a Phillips screwdriver, channel-locks, wire cutters for zip ties, replacement zip ties. Just watch some guys demonstrating how it’s done. You have to close the right valves and have a bucket to drain water into. But you can do it. This part worked perfectly and now we have hot water again.

Suddenly lost hot water, which with a family of 5 in the winter is rough (no hot showers!). Our model is the NR-240A and it was not displaying an error code. Performed a full maintenance list - cleaned the air intake, descaled via vinegar flush, cleaned the water filters - still nothing. Tried the trick to release the over-pressure valve to no avail. The burners would start to light for a couple seconds, but once the full demand started and the fan really kicked on, the burners would immediately stop. I read somewhere that no error code may likely point to a faulty flow sensor, so I took out the old flow sensor, performed a visual inspection and saw nothing notable. Soaked and cleaned with vinegar, blew out with an air compressor, and put it back in - still wouldn't heat. At that point gave this new part a try. Once you know what to do (I used youtube), replacing this part takes one minute. So I put in the new one and - it WORKED. I was so afraid it was something worse, like a failed internal recirculation pump... but replacing the flow sensor restored it 100%, at least for this situation. Family is now enjoying hot showers and happy once again.

My Navien went down, took the error code, found I needed a part. Amazon to the rescue! Simple replacement, saved a service call (and some $$). Remember to flush your system with vinegar every year.

Exactly like the original part in the Navien water heater. Very easy to install if you are handy—about 15-20 minutes. Just watch one of the instructional videos on YouTube and follow the step-by-step instructions. I installed the new sensor the day it arrived. The water heater is working like new again. Saved a lot of money doing it myself!

There are two images of the impeller that triggers a hall effect sensor screwed to the outside of the sensor body. The sensor very seldom fails but , in this case, and i suspect many more like it, the cause of the problem is the inadequate sealing of the impeller shaft within the overmoulded plastic impeller. Water eventually makes it's way down the shaft and starts an exfoliation type of corrosion that causes the iron core of the impeller ( the magnetized item that provides the signal for the hall effect sensor to count the number of rotations and convert that to a flow rate in liters per minute or whatever unit they use) to expand and break apart the plastic overmoulded impeller and render it useless as a signal source. The stack of magnets has a couple flecks of the exfoliated magnet material stuck to the face of the magnet stack (not a part of the unit just a demonstration of corroded metal) , material easily picked off with a fingernail. If you really want this thing to last the life of the unit, it's easily disassembled and a very small amount of, say, waterproof JB Weld, could be applied to the shaft on both ends and radiused out over the face of the impeller to create a water impervious seal for the shaft. Delicate work to be sure but probably not worth the effort given the replacement cost. So...there you have it. Now you know probably why your unit failed in the first place.

OEM replacement. Job was super easy. There are some videos out there to show you how to do it. We did call the plumbing company that installed the heater but when they didn’t return our call we did it ourselves

It took time and frustration to figure this out. Calling Navien technical support lead me to this solution after going through the maintenance steps did not help. The part is cheap and easy to replace. Navien sent me the first one for free saying that they fixed the original issue. Since then I have replaced the part over five times. I always have a spare sitting on top of the unit waiting to be used. It takes five minutes but before I had a spare, I had failures around holiday weekends and had to drive for hours to pick the part from the only open location or else I had to wait a week without hot water. My rating is low because this has become an annual step. This unit fails about once a year. Showers start to not be warm because the flow sensor fins break down and do not sense the actual water flow. Navien should make a better part and send it to its customers. Instead, they talk about how old the unit is. Everything else works. One cheap part causes people to spend lots of money on professionals and damages the reputation of Navien. If you don't know how to fix it yourself, its better to get a water heater elsewhere. If you are comfortable with this simple repair, get a few spares and place them on top of your unit.

Over time and depending on the amount of solid particles in the water stream, the blades of the turbine meter will wear. The result will be less heat delivered to the water. Check out YT videos for Navien water flow sensors.

This is exactly what is advertised. Not sure if Navien will improve the design but the original lasted 12 years so I am sure I won't need to worry about this one again while I am in this house.

Works like a charm! Like so many others, my Navien heater stopped working and this little part was causing all the trouble. If this helps someone, I own a NR180A heater, and the part this replaced was # 30011024H, which is no longer available. This is part # 30010537A and looks exactly the same, and is of exactly the same dimensions. It was a plug and play replacement, no need (or space available) for packing nuts, or additional O-rings, or the $350 price tag I got quoted for this fix. All I needed was a screwdriver, a wrench and about 10 minutes. I ended up reusing the wire from the original part instead of the one that came with this.

Fits perfectly

The Flow sensor was easy to install and worked great for 10 months and now failed, giving error 038E on my Navient NR-240A.