I have lived in my house now that we built for just about 8 years. Something that always bugged me was the performance of the dual Rinnai RL94 units the original plumber installed. For some reason this has been the year of “water” for me and I started paying more attention to how these units were performing and realized something very astounding. While they appear to be plumbed correctly, they were not “connected” to each other. I am not sure how many people have a residential dual installation but if you want to learn more please read on. What I have found is there isn’t much out there on this topic.
I did a lot of digging and found this training guide, of which the most interesting pages are the last few. This is where it talks about multiple units in parallel. Now it stands to reason if you read this that multiple units connected to the same cold water line essentially have their activation flow “multiplied”. You can read the example that 5 units effectively would need almost 2GPM to fire (.4GPM x 5 units). In my case I have dual units so the combined flow rate for both to fire is .8GPM.
While this may not seem like a lot I started finding that the left one might light, or the right one, or both, or in some case NEITHER based on the faucet in use. In my case the main issues were the Delta Touch2O kitchen ones with 1.8GPM heads and a single hot/cold mixing valve. Really it was a craps shoot, and I started reading the next page that discussed an EZConnect Cable that you can use with only 2 units. Beyond two units you need the full MSB setup but I decided to go look and guess what….NO connection between the units.
I called Rinnai and started to ask exactly what does that cable or the MSB do? If you read the training doc it is very basic, but you end up with a Primary unit and a Secondary unit. The primary controls the flow servo control of both units and the temperature, ensuring that based on demand either one is running or both. The difference without it is they are just independent units with no intelligence. In my case if one happened to fire water was still FLOWING through the other but not being heated. This resulted in cold water being introduced to the hot water line randomly.
According to the tech the link between the two monitors demand and not only opens the flow control servo but sends a light signal to the secondary to ensure if water it flowing it is also being heated. Holy cow, how did this get missed on the install?!
Pre EZConnect Testing
I did a simple test of the split flow rate requirement with a dual handle faucet in the basement near the units. With one unit’s inlet and outlet valves both closed I slowly opened the hot side until the only available unit started to fire. It’s say it was roughly 1/4 – 1/3 open at the time. I then went and opened the inlet and outlet valves of the second unit. If the documents were right it would take double the flow to light one or the other or both. This did appear to be true in fact. I had to open the hot side over 1/2 way to 3/4 before anything lit and they both started not one or the other. This proved the independent nature of the flow rate activation problem.
Post EZConnect Testing
Once the EZConnect was installed, which is very simple to do according to this instruction manual. The key is that the unit where this is plugged into the PC Board is by default the Secondary unit. In my case I also have the primary unit managing the recirculation loop and both units via the dip switch settings. These both hard the Control-R installed but that proved problematic for the recirculation. Also due to the way it was plumbed I found having BOTH the lower recirculation values open seemed to work best. When the primary unit calls for recirculation the pump feeds both units, they both light, and then the primary shuts down the control valve on unit two and keeps heating.
This setup has been running this way for over 2 months and now seems to work as best as I can get it too. The control cable was the key, but in hindsight the plumbing could be altered to not even have the dual incoming cold feed from above since it’s in line with the primary unit’s feed for the expansion tank. All in all the cable was the key along with a few other tweaks including disconnecting the Control-R modules. I could try seeing if those work again with only the primary controlling the recirculation schedule but with the EZConnect Cable it always seemed like control was getting confused in some way as that “takes over” the controller function from the front panel.