Rinnai RL75i Tankless WH

[AndrewS]

I just purchased a home a few months ago that has a Rinnai RL75i LP tankless water heater. I will start from the beginning, I was having sediment issues and after some trial and error with salt-free softener and filters I finally found that my water heater is the cause of the sediment I was getting. To resolve the issue with the shower heads, aerators and screens getting clogged every couple of days I found and installed a water filter designed for hot water after the water heater and that has fixed my problem. Fast forward to yesterday, my wife used hot water throughout the day, I came home and showered - no problems. Then we ate dinner and when we were trying to clean up - no hot water. I go take a look at the heater and find error code 14 on the display, which indicates the water heater is overheating. So I did a little googling and decided to flush the heat exchanger for a bit and see if that helped, to no prevail. Now the water heater will fire up and work for about 30 seconds before it pops the code and shuts down, so I don't believe I have a bad thermal fuse or it wouldn't fire up at all? This morning I woke up tried the shower, same problem worked for a few seconds then shut down. Then I turned the water off and on a couple of times and voila the hot water worked the rest of the morning. I am looking for suggestions as to the cause? I plan to go home today and run vinegar through the heat exchanger for a couple of hours - but it just seems odd. I am thinking if the heat exchanger was clogged I would have reduced pressure coming out of the heater, and since it will work every time you turn the hot water on, although maybe only for 30 seconds that tells me the thermal fuse and safetys seem to be working properly - so I'm trying to figure out what is causing the overheating - which I can now say is intermittent. Any help or ideas are greatly appreciated.

 

[RS]

It doesn't make any sense to me to install a filter after a water heater! I always install filters before the softener to keep the sediment from plugging the screen in the softener. Also I don't see how a water heater can be the cause of sediment! Are you on a well? Any water source can have sediment, and it's best to filter it out as soon as possible. Your water heater is probably plugged with sediment, and needs to be flushed.

 

[AndrewS]

Originally the house had 1 filter after the pressure tank. I tried a salt-free softener and it made no difference whatsoever, then started leaking. So I replaced it with another filter, so I have a sediment filter and a charcoal filter. From my understanding, tankless water heaters heat water so quickly it precipitates sediment due to the rapid heating of the water - I have no sediment at all BEFORE the water heater, last night I got about a 1/2 to 2/3 cup of white sediment from the bottom of the filter after the water heater, again NO SEDIMENT at all in either filter where water enters the home. I tried several things before I resorted to this and the filter after the heater is the only thing that corrected the problem. The only reason I can figure is that the water heater is what is causing the sediment, if you have a better understanding/explanation please fill me in. Also, as I mentioned in the first post, I flushed the water heater last night and was still having an issue afterward.