Hi
We have a home build in 5/14 with a Navien tankless water heater. Everything has been great up until about 6 weeks ago when we started having supply issues with the hot water. We have dual shower heads in the master shower, one runs cold while the other runs hot. Right now, we have to run #2 at the same time just to get #1 to run hot. What???

We had one plumber come out and quote $325 to flush the tankless. No thank you. And $220 to replace the Delta cartridge in the #2 shower head in the master. Delta sent me the part for free...(not $80 as he said) I sent them away.

2nd plumber sent from builder cleaned the filters on the Navien (they were filled with debris) and adjusted something on the showers. Seemed to work. Still no hot water in #2, the bathtub, the kitchen or upstairs showers.

3rd plumber from same company flipped the switches on the Navien and said that should do it. At the time, I had hot water in all areas and he left. 4 hours later....same issues.

Now plumbing company is coming to replace the water heater next week. My question is.....what is going wrong? Nothing has changed with the configuration of the pipes. So when Navien (I called them directly) said it was probably in the plumbing, I scratched my head.

The house is new construction...less than 2 years old. Why is hot water getting to some areas and not others when it all worked well until recently?
Thanks in advance for any insight.

These tankless heaters need to be flushed on a regular schedule. As there is no tank for the debris to settle in. You could also invest in a small filter to put inline to heater to reduce the scale. But regular maintenance is a must on these or they will fail.

quote; We had one plumber come out and quote $325 to flush the tankless. No thank you

DId you expect him to do it for free? It is a labor intensive process, especially if it has not been done on a regular basis. Did YOU "flush" the heater, but flushing is not the true process.

I have a couple of tankless water heater units in service. I try flush them every 6 months with vinegar. When they were installed we used a set of valves that can be used to isolate the unit from it's normal water supply and use a 5 gal bucket with 3 gallons or so of cheap vinegar in it and a small submersible pump to circulate it through the unit. Gas is turned off of course. Just leave that plugged in for about 4 hours, then flush it with water and reset the valves.

It might be a bit more work if it was not installed with the valve set to allow easy flushing.