Changing a Navien water sensor valve

This part is also called a water servo valve, its purpose is to fire up the tankless as water passes through the unit.
This is problem the most troublesome problem you will get with a tankless heater.
Most of the time it is caused by not flushing the cold-water piping on a new installation or if the water was shut off in the house and debris enters the servo valve.
Remember to check the inlet water filter to ensure that its free of dirt.
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I hope you enjoy the video,
Mike
PLEASE USE A LICENSED PLUMBER TRAINED IN NAVIEN LEVEL THREE CLASS. FOLLOW ALL STATE AND NATIONAL PLUMBING AND GAS CODES AND TO FILE A PERMIT WITH YOUR LOCAL BUILDING DEPARTMENT.

[@briancarlisi2224]

Great job!

[@Brooks.Mechanical.Electric]

The thermistor of the valve, is it a kohm thermistor that can be tested with a multi meter?
If so, do you know what the resistance valve would be at a specific temperature? Many manufacturers of equipment i service will provide a resistance chart, nut will give a specific resistance for 70° or something similar.
Another question is about the gas valve. I have had to test inlet and what we call it in furnaces is manifold pressure ports, but just curious if on a Navien can the manifold pressure be adjusted or is it set from the factory? I have worked on some Bosch units that wouldn't light because of over pressure conditions, but I could only adjust it at the regulator, not the gas valve.

[@mikejunior3322]

Sir what is the name of that part that you just cleaned the valve that has a 4 screws thank you

[@TomBo501]

He states it is called...water servo valve. I call it a flow sensor. I just had the same model NPE240A2 diagnosed by Tech Support at Navien over the phone today (7/2/24). Sympton was low hot water temp at all faucets. Flow rate on screen of tankless WH showed 0.7 GPM and I know there was at least 1.7 GPM flowing through it. Tech Support zeroed in on the issue fairly quick. It was the check valve not the flow sensor (water servo valve). There is a bypass valve inside in the lower left corner as you face the unit labeled INT and EXT. Valve arm swings 90 degrees. Tech Support had me turn the arm from INT to EXT which bypasses the holding tank (so these units do have a tank, just very small) just above it. The flow rate on the WH now showed the correct flow rate. They determined the check valve was defective. Being held partially open. My unit is still under warranty. They FedEx'd a new check valve to me overnight. I'll replace the check valve tomorrow. Looks very easy and simple. They did state instructions are included with the new part. Here is a UA-cam video on replacing it if that is your issue.... ua-cam.com/video/Y76PrCV2ho8/v-deo.html Not the same model as mine in the video but you can see what the check valve looks like and how to replace. I worked for a month trying to figure WTH was wrong. My Navien would work fine for a few days to a week and then fail. I would power cycle the unit and most of the time it started working normal. Today it failed and no matter what I did, it would only show 0.7 GPM on the screen and only get luke warm water at any hot water faucet. So glad it is finally resolved. These videos about the Navien are AWESOME!!! Thanks UA-cam Creators...much appreciated. Tom

[@TomBo501]

I got the INT and EXT positions reversed. Tech Support had me move the arm from EXT to INT. Sorry about that. Basically whatever position it is in before doing anything....change it to the other position and test the TWH again. Tom