HOT COLD HOT COLD

[Leeway317]

So, after roughly 9 months of use, our Rinnai Tankless started asking up. It get hot in normal time at the shower (opposite end of house), after 3 minutes, it gets ice cold. I shut the shower valve off, wait 15 seconds, turn it back on, it gets hot in normal time, 3-4 minutes later, it goes cold again. Repeat. Yell out curse words, repeat again. Then it gets hot and stays hot for as long as needed. This happens more times than not, but not every shower. What's going on?
An added piece to the puzzle, the gas company stopped by today and checked my exhaust and said my water heater was emitting 1200ppm go unburnt gas. Can that be related to whats causing the temp loss? Is 1200ppm normal and nothing to worry about? Gas guy said that number isn't "high", but I don't know if it could still be a hint as to the temp problem but still not be an efficiency problem.
Any ideas?
Someone told me flushing it would fix the temperature problem. I don't buy that.
Someone else told me that if I had the temp setting above 120, it could cause that problem. I did actually have it set at 140, so I set it back to 120, problem still exists.
Any help would be appreciated!

 

[WorthFlorida]

From Rinnai web site: All tankless unit required maintenance, not like standard water heater that can go years.


What type of regular maintenance does a Rinnai Tankless Water Heater require?

There are two types of periodic maintenance that your service technician should perform to keep your Rinnai tankless water heater in top shape. It’s important to note, the time in between necessary maintenance will depend on the water quality in your home.

1. The in-line screen filter should be checked periodically for debris and cleaned.

2. The unit should be flushed periodically to keep it free of scale and lime, which can shorten the water heater’s lifespan over time. This process should be completed by a professional installer. Please contact an installer near you.

Our How to video just in case you want to do some maintenance on your own.

Read the full article from Fine Home Building - Master in a Minute Video: Tankless Water-Heater Maintenance

 

[Sponsor]

 

[Fitter30]

That 1200 reading Carbon monoxide ( Co) reading should be under 10. Co reading is incomplete combustion. Someone with a flue gas analyzer need to look at heater now. The heat exchanger could be compromised. From high TDS
WorthFlorida wrote. Heater have a inspection window to see the flame should be blue color might have slight yellow tips.

 

[John Gayewski]

You likley need someone to come look at it. Sounds like a sensor. I don't think it's related to the gas or cleaning. Although they do need cleaned 9 months seems a little soon have a scaling issue.

If you unplug it and plug it back in and the issue resets and starts over it seems to be electrical. We usually work on Navien so experience with this brand isn't in my wheelhouse.

 

[Fitter30]

So, after roughly 9 months of use, our Rinnai Tankless started asking up. It get hot in normal time at the shower (opposite end of house), after 3 minutes, it gets ice cold. I shut the shower valve off, wait 15 seconds, turn it back on, it gets hot in normal time, 3-4 minutes later, it goes cold again. Repeat. Yell out curse words, repeat again. Then it gets hot and stays hot for as long as needed. This happens more times than not, but not every shower. What's going on?
An added piece to the puzzle, the gas company stopped by today and checked my exhaust and said my water heater was emitting 1200ppm go unburnt gas. Can that be related to whats causing the temp loss? Is 1200ppm normal and nothing to worry about? Gas guy said that number isn't "high", but I don't know if it could still be a hint as to the temp problem but still not be an efficiency problem.
Any ideas?
Someone told me flushing it would fix the temperature problem. I don't buy that.
Someone else told me that if I had the temp setting above 120, it could cause that problem. I did actually have it set at 140, so I set it back to 120, problem still exists.
Any help would be appreciated!

Couldn't find any info on burner flue gas specs but having set up hundreds of burners none have called for anything like the gas company wrote. You didn't state what the 1200 is. Flue gas setting is O2, Co and excess O2. The only reading at 1200 is Co so I'm confused what they were looking at. My combustion
analyzer hit 1200 i would be running to pull it out of the flue before it went to fault and may be live again in a hour.

 

[Leeway317]

You likley need someone to come look at it. Sounds like a sensor. I don't think it's related to the gas or cleaning. Although they do need cleaned 9 months seems a little soon have a scaling issue.

If you unplug it and plug it back in and the issue resets and starts over it seems to be electrical. We usually work on Navien so experience with this brand isn't in my wheelhouse.

I’m going to try that. If my memory serves me correctly, I already did but not positive so I’m gonna give that a shot, thanks.

 

[Leeway317]

Couldn't find any info on burner flue gas specs but having set up hundreds of burners none have called for anything like the gas company wrote. You didn't state what the 1200 is. Flue gas setting is O2, Co and excess O2. The only reading at 1200 is Co so I'm confused what they were looking at. My combustion
analyzer hit 1200 i would be running to pull it out of the flue before it went to fault and may be live again in a hour.

Yeah, unfortunately I wasn’t home when this happened. The gas man was checking for leaks, which I assume was just out of precautionary reasons. According to the wife, he said he noticed my concentric exhaust pipe sticking out about 10’ away so he, “according to her” figured he’d check the discharge content and told her, “it was releasing 1200ppm of unburnt gas”. That’s all I was told so that’s all I have to go by. She did say however that he told her “it’s no big deal”…assuming he meant it wasn’t a concern.
So I set out to find normal burn rates for this unit but couldn’t really find any rates for any tankless unit. So here I am. Having been a plumber my entire life, I’ve often times have seen this site so I figured I’d ask here. Hell, asking the guys at the supply house counter these days is like asking someone at Lowe’s. They just sell it, they don’t know much about it. Although I don’t have much room to talk here. I can, and have, installed tankless WHs but I am not a service tech on the units by no means.

 

[Fitter30]

Nat gas
Co2 high fire 9.0% O2 4.9%. Co less than 200ppm
low fire 8.9%. O2 5.4% Co less than 200 ppm

Lp
Co2 high fire. 10.5%. O2. 5.4%. Co less than 200 ppm
Co2 low fire 10.4%. O2 5.4%. Co less than 200 ppm