Question about Rinnai Desa Vent-Free Infrared Gas Heater: Vent-Free Infrared Gas Heater(18,000 BTU)

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Rinnai R53 Natural Gas Tankless Water Heaters

Noise and inconsistent temperature delivery are my complaints. I had two new Rinnai R53s installed 8 weeks ago. They are controlled with a single control panel in order to work together. In theory, I should not run out of hot water but there is something wrong with how the water is mixing. The 1st floor thermostatic valve double shower located directly above the units, which are installed in the basement, gives the only consistently warm shower. I also have no problem running only hot water, the problem is when I call for a mix. When my 2nd and 3rd floor showers are calling for warm water (one is an old fashioned hot and cold faucet set and the other is a new tempress dual pressure valve) the water fluctuates like a sine curve between hot to warm to cold to warm to hot. This is after the expected 2 to 5 minute wait for the hot water to reach these floors. It makes for a most uncomfortable showering experience. This is also happening at all of the sinks. Also, when anyone turns on any hot water tap, there is incredible groaning noises in the 2nd Rinnai unit and the whole house vibrates from the sounds. They have a dedicated natural gas line.

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  • marbleharbor Aug 21, 2008

    Rinnai, tankless hot water heater, natural gas. Groans or vibrates when

    there is a call for hot water. Also occasionaly has a momentary lapse in supplying hot water. Unit is only several months old.

  • Anonymous Nov 07, 2008

    I have one unit and it makes groaning noises too when it first starts out..after 1 min, the noises stop and unit operates ok...

  • Anonymous Nov 11, 2008

    My hot water pulses. It is pulsing from the tank. If I turn on hot in my basement sink next to the unit it runs hot for thirty seconds then it turns off untill cold water runs through the unit. Then it turns itself back on.


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It sounds like the Rinnai units are working correctly but you've got some plumbing problems.  Any tankless heater has a minimum water flow required to keep the burners going.  If the burners were going with very little water flowing through them to carry the heat away, the heat exchanger could overheat and fail.  The solution is generally to the electronic controls to set the desired temperature and then just use hot water.  Once you start mixing cold water in, you actually reduce the flow of hot water and the burners turn off.  If you are right near the cut off point, the burners will cycle on and off resulting in those very annoying hot-cold-hot-cold showers.  
The fact that you've got those very loud noises indicates some other sort of plumbing problem.  Hooking up two tankless units in series is much more complicated. In heavy draw situations, the second unit is asked to finish heating the water up to temperature when the first unit couldn't quite get it there. Now you're putting hot water into a heater and heating it more.  You have a lot more issues with fluctuating temperatures and pressures within the pipes which could conceivable cause these horrible noises.  Everything's got to be set up right to for things to function properly and it's easy to get something wrong.
From your description, it sounds like a better solution would have been to mount the two heaters in different places. e.g. One in the basement to serve basement and first floor faucets.  The other on the second or third floor to serve those two floors.  Since these units are direct vent (don't use inside air), they can even be mounted in a closed closet as long as the vent can get to the outside.  With this setup you avoid the complexities of a series installation and you also have a much shorter wait time (and therefore less waste) for the fixtures on the upper floors. 

Posted on Jan 22, 2009

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FWIW, the most common problem with tankless water heaters is under-sized gas piping - they need a LOT of gas RIGHT NOW. They do use less in the long run, though.

Another common problem is incorrect venting. A cross-connection between hot & cold water piping will also screw things up.

The best people to talk to about it is the manufacturer. If the heaters are new, they're under warranty - you should take advantage of that.

Posted on Apr 10, 2009

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I have the same problem from time to time, adn I concluded it's a water pressure issue. I solve the problem by running hot water through as many pipes as possible to stabolize the pressure. I havne't figured out a fix yet, but I think it's a water piping issue.

Posted on Jun 11, 2008

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Now to me this would result form not enough water going into the system. do you have a seprate unit on the bottem to take off and clean?

Posted on Mar 31, 2008

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