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r85 rannai problem

stanguy Member Posts: 2
When I first had my house built, the plumber hooked up 2 rannai-85 heaters side by side operating in the same line. In essence both heaters are heating the house when only 1 faucet is on. From day one, it has taken forever for the water to get hot(im talking several minutes) and even after it gets hot, it randomly gets cold. no matter what i set the controller at it does this. Would taking out 1 heater help alleviate this or are the units too big? The water pressure seems fine and all faucets really spew out the water. when I shower it works fine when I run the shower and sink together. Is one rannai countering out the other or what im so confused. ive had several plumbers out and they havent a clue honestly. this is a pic of the setup. please help.


  • stanguy
    stanguy Member Posts: 2

    Ok, after doing a little research it seems that cold line goes into both heaters and hot comes out both and into house. From my understanding it seems that cold is supposed to go into one then hot out and into the other then out and into house like shown in the drawing that i supplied. maybe this would help. also there is only 1 controller running both heaters.
  • Jack
    Jack Member Posts: 1,047
    If the Rinnai's are not throwing an error code

    I'll say that they are "functioning correctly". Faint praise under the circumstances, but lets look at it. Your drawing is incorrect. Yours is a "series" lay-out where, for high capacity you want the "parallel" piping.

    I believe you have the MSA control on the 85 to join the operation of the two units. With this control the units function as one, modulating together and rotating the staging automatically. This can be an excellent lay-out...depending upon the configuration of the plumbing system. If the bathrooms and kitchen are widely spaced it is frequently best to split the units up. One on either end of the house.

    I think what you are seeing is a flow issue. The R85 will fire at a flow rate of .4gpm and fire as low as 10kBTU. It will hold operation down to .25, I believe it is. I'm a bit rusty on that unit, but I think those are correct numbers. When the MSA control,is added, the minimum flow rate goes to, I think it is .6 gpm

    Get your install manual out and look at the page that discusses the sequence to read flow on the controller. You are going to put your track shoes on as you need to read the flow rates by each fixture. By doing this you can develop a schematic of the system and exactly what is going on. As well, how far away are the fixtures from the water heaters? Consider both the length and rise in this calculation. Do you have a recirculation line on the hot water system? Do you have a basement or an easily accessible crawl space? I would suggest that you also check out www.gothotwater.com.

    Oh, and also, turn off the supply valve on one unit and run all the time and temp checks that way too. These flow/time checks should be done with cold water through-out the system. So, turn the 85's off and run cold into the system. Turn them back on and do the flow check. Tedious, but necessary to understand your system.

    How many baths room, kitchen, high flow fixtures do you have in the home? Curious why two units are installed. I apologize for making you do all this, but with this information we will all have a better understanding of what you have. Only then will we be able to understand the solution.
  • RobG
    RobG Member Posts: 1,850

    I agree with everything that Jack said. The only thing that I would add is that allot of these units are sold as "instantaneous" water heaters. That is simply wrong. The units are "tankless" water heaters. The energy savings is in not maintaining a tank of hot water while you are not using it. If you had a tank of hot water in the same location as the Rinnai units it would take about the same amount of time to get hot water at the fixture (probably a few seconds less due to the pressure drop through the tankless"s heat exchanger). However you would still use the same amount of water while waiting for it. Follow jacks instructions, try shutting off one unit then the other and see if there is any improvement. You could always relocate one of the units closer to the furthest fixtures or install a recirculation loop. I've had one in my home for about ten years (different brand but same animal) and have never had a problem. I located it right under the area where my baths are and don't have to wait more than twenty seconds. the kitchen takes about a minute as it is on the other end of the house. I wonder if you may have water pressure issues? As the units are on the outside of your home I assume you are in a mild climate. Some homes only have a 1/2" water line supplying their home in some desert environs. That could definitely slow down the hot water delivery.