Rinnai R94LSi Flushing Problem

[Philwgreen]

I have 2 Rinnai tankless water heaters and I've been flushing them on average about every 18 months. Today, I was flushing both heaters. The first one had no issues. However, the R94LSi has no pressure on the hot return hose back to the bucket.

With the gas turned off and the unit unplugged:

1. Connect a hose from the pump to the cold isolation valve.
2. Connect another hose from the hot isolation valve and place the loose end in the bucket with the pump and vinegar.
3. Close the hot and cold main lines.
4. Open the hot and cold isolation valves
5. Turn on pump

The pump runs and vinegar comes out of the other hose for about 5 seconds before completely losing water pressure. From that point on, it's just a trickle. To test the hoses I removed the cold isolation valve hose, placed it in the bucket and turned the pump on - full pressure. With the cold main on and the hot isolation valve hose attached, I can open that valve and get full pressure as well - so it doesn't seem to be a problem with the hoses.

Has anyone run into this issue before? Is there something simple I'm missing?

 

[Philwgreen]

Quick update. I tried again and got a little more flow out of the return hose. If I turn the isolation valve on and off quickly about once every 30 seconds I can keep the flow going. It would be pretty hard to do that for a full 45 minutes though. The only reason I think that works is it's building up enough pressure behind the closed valve - but the real issue is whatever is restricting the valves.

Could the isolation valves themselves fail is some way? It seems fairly impossible for the ball valves to fail - but I wasn't sure if there was something else going on inside the isolation valves that could restrict flow.

 

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[BDoody]

Hi Phil,

I'm having the same exact problem with a Rinnai R75LS. Any luck finding a fix that works besides working the valves for 45 minutes.

Thanks!

 

[Philwgreen]

Sadly no, it turned out to be a mess that involved replacing the entire tankless unit. Replacing the entire thing instead of just the valves wasn’t 100% necessary but I had been having some other issues with that unit and decided to just replace everything at once.

 

[Terry]

Sadly no, it turned out to be a mess that involved replacing the entire tankless unit. Replacing the entire thing instead of just the valves wasn’t 100% necessary but I had been having some other issues with that unit and decided to just replace everything at once.

When were the tankless units installed? And what is the water like where you're at?
Tankless is a new technology and we're learning as we go.

 

[Philwgreen]

The unit was installed in 2011 - the second unit was installed in 2013. The water is fairly hard here as well. The main issue was the water was the water was getting 'cooler' as the years went on with the first unit. By the time I replaced it, I had it set to 130 degrees...and it felt like it did when it was set on 120. I had assumed that was from build up inside - and looking back on it now flushing every 18 months was probably too long to wait between flushings given the hard water here.

However, I was in the process of moving and getting the house ready to sell, which is why I went ahead and replaced the unit. Normally, I would've just switched out the valves to start