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Rinnai Water Heater - Water Not Hot Enough

Our house was built in 2009 but this problem has existed ever since we bought it and it's gotten to the point that I should figure out how to fix this issue.

We have a Rinnai R75-LSi and next to it is a Heating Box KD-HBO100. I don't have a great idea of what the concept of the Heating Box is.

Anyway our house is part of a townhouse complex and all 8 townhouses have this issue. The first time I tried to take a shower, I noticed that the water was not hot enough for me so we called the builder of the house and asked why. He said we needed to turn on the heat with the thermostat and let the water run for 5 minutes. We did that and it worked - the water could get really hot and I thought it was fixed. The next day the same problem returned.

One of my neighbors thought it could be an issue with the electrical system and we had an electrician come by to fix it. I assumed he fixed it and I let him on his way but later that night it turns out the issue was not fixed.

In the summer, the water is fine and warm enough for a shower but come winter time every time you want to take a shower or wash the dishes, you need to turn on the heat first with the thermostat then run the water while the heat is on.

After some testing with the electrical outlets, I noticed that the electrical outlet where the Heating Box is connected to doesn’t have electricity and when you plug the Heating Box into the electrical outlet that the Rinnai is plugged into, the Heating Box turns on and just stays on. If you plug the Rinnai into the electrical outlet that the Heating Box is connected to - it doesn’t turn on. What confuses me is that when you turn on the heat through the thermostat, the Heating Box will turn on and run even though the electrical outlet doesn’t work. Not sure if it’s designed this way.

I tried leaving the Heating Box unplugged and just using the Rinnai water heater and the water doesn’t get warm enough – so it seems like Rinnai alone doesn’t get the water warm enough in the winter and needs the Heating Box to help warm up the water. My problem is how do I get the Heating Box to activate without having to turn on the heat through the thermostat or is that not the problem here?

I appreciate any help possible.


  • Zman
    Zman Member Posts: 7,572
    Free Lunch?

    What you have is a instantaneous domestic water heater. It is designed to heat domestic hot water. If it was sized and installed correctly it would do just that.

    It appears that your builder was convinced it could be used to also heat your house. The heating box product is supposed to allow it to do that. There are numerous reasons this is a bad idea. Legionella  bacteria being one, durability is another.

    I don't have any experience with the heating box product, nor do I want to. I think it is safe to say it will not work unless it is powered up. Beyond that ,they may have a tech support department that could help you.

    The real solution is to install a system that is designed to heat your house.

    As Dan says, "there is no free lunch". You will pay more to do it right.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • heatpro02920
    heatpro02920 Member Posts: 991
    edited January 2013
    do you have a picture of the system

    I would like to see a picture of the system, it sounds to me like the heater units thermostat is wired either 120v to the outlet or to a switching relay that feeds the power when it calls for heat, either way I have never heard of that being done before...

    I suggest first getting some pics up here so we can tell what is actually going on, it may be as simple as getting a control that allows the temp to go higher, or maybe getting another unit for your domestic water and let the heating system handle the heat....

    Did you ever take the cover off the navian and see if there is 2 pumps or one pump inside?
  • Henry
    Henry Member Posts: 998
    The Great White North

    We have refused to install instantanious heaters since around 2006. Thye cannot meet the demand of NA houses! They work inJpan, China and some parts of Europe but not here! The temperature rise quoted does not meet our 100F PLUS! Besides all the service issues! Stay away!!!
  • Jack
    Jack Member Posts: 1,047
    My Henry, but you are persistent

    with this comment. I'd be interested in your story on this topic. It is hard for me to believe that all those few hundred thousand people per year who are buying them are unhappy;)

    To the original poster. Put a hose on the hot water outlet service valve and close the valve to the system. Set the unit to 120 and read the outlet temp on that water. That will by-pass your system entirely and give you a good hot water test. Get you install manual and get the sequence to read output temp and GPM of hot water flow. Report back!
  • icesailor
    icesailor Member Posts: 7,265
    Sorry Jack but:

    Sorry Jack but Henry is correct. Although the instantaneous or tankess heaters do work, they have "issues" and do not work as well as advertised. They are difficult to service and parts are always an issue.

    I bought a well known commercial 199,000 BTU brand that I used feed a 50 gallon storage tank for a high load commercial use. No matter what I have tried, I can not get the heater to run over 140 degrees. Tech support told me to connect to the wire with the 160 degree flag. As many times as I have tried, I have not found any wires with that flag. When the heater gets to 130 degrees, it isn't even running at 60% fire.

    I've used them to feed mixing valve applications in a nursing home where the hot water circulated was 112 to 116 degrees and you didn't have enough differential to have the thermostatic part of the valve work. Install a Ranaii and feed it with 130+" degree water and the problem goes away. Not so with my other application.

    I understand what Henry is saying. Some folks will accept anything. The heaters are sold as something that they are not. Some customers are picky, Picky.

    I just replaced a leaking direct vent tank type water heater. The owner asked about an instantaneous. I gave them all the pros's and cons. Including a new gas line, increased to 3/4" to feed the new heater. The change in venting, and the possible problems they might notice where intermittent draws cause cycling and they might find it objectionable. The cost of install of the Instantaneous was not all that much but the problems of there no hot water during on/off hot water and the lag in gas fire during it. I would have been happy to sell them an instantaneous. They chose a new direct vent tank type.

    Its not my job to convince them to use something that they might not be happy with and blame it on me. I've been hunting with that dog before and I didn't like it.
  • heatpro02920
    heatpro02920 Member Posts: 991
    edited February 2013
    I have installed a lot of tankless units

    I see a few guys on here are set against tankless units, I have installed hundreds of Rinnai units, dating back to the day they were released for US sales... The first one being in my own house {which is now rental property} and it is still working like a champ { I believe it was like an r53}, two baths with a jacuzzi, never had a problem... With new england city water...

    I have installed them on well water also, my current home has 2 ru98i's with well water {not the greatest well water either} and they are working as they should... Plus hundreds of customer who never call me to say they are having problems... I can count on one hand how many failures I have had, and I have never had to replace the entire unit or a heat exchanger to date...

    I do recommend flushing units with well water, and I like keeping them set a 120 degrees, and make sure the gas piping is sufficient, and they will run for a long time...

    On the other hand I have had a lot of bad luck with Bosch and takagi units and now I wont even service either of which...

    I have installed them in restaurants with multiple storage tanks, in at least 25 radiant heating systems, and I have now seen them run Hydro air units efficiently with a little finesse {I recently had a post about this}...

    I find nothing wrong with them and if you know how to fix them and maintain them, they can make your company profits like no other device on the market... I can attest to that...

    Also they are so easy to change I have a spare propan and a spare NG unit at my shop incase we ever run into a problem that is either not easy to figure out or parts arent available. I have only had to do this twice, once was a propane unit on well water that kept sooting up turned out the backup one sooted up just as fast, ended up being a bugs nest in the intake pipe, other one had a bad gas valve, was covered under warranty but didnt have it in stock so I through a spare up there until the customers unit was fixed....

    Now most of the calls you get are easy to fix and not related to the rinnai, I have had the well pump set to low before it kicked back on which made the rinnai kick off once and a while from low pressure and then come rite back on, giving the customer a cold sandwich, then I have had a couple "not enough gas problems, with NG and LP, also not the units fault, it fires up to 200K it needs gas... I also had washing machines that have bad mixing valves in them make the Rinnai unit seem like its not making enough hot water, when the faulty washer was mixing it backwards.... And lastly scald valves in some faucettes and shower valves, will drive you crazy, because they drop out flow once and a while and shut the rinnai unit down for a second, also giving the customer a cold sandwich... But these are all problems a good installer will check for initially and tell the customer, "I have to disable the scald valve in this shower" , "I will need to run a larger gas supply to your water heater", or that washer has a mixing valve in it that may someday fail and give you hot water issues... Like with everything else in this business the installer sets the playing field, the rite techs can make all the difference...
  • RobG
    RobG Member Posts: 1,850
    Water Heater Problems

    I can't quite tell from the pictures but the gas line going to the unit (the yellow line) looks like it has a kink in it. If that is the case, you must get that repaired before you can proceed with any other trouble shooting. If a tankless unit is starving for gas it will never work properly.

This discussion has been closed.