Question about Rinnai R75LSi Tankless Water Heater 180,000 BTU R75LSi

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Rinnai R75LS - Water not getting hot anymore even though internal sensor output shows max temp.

Unit over 3 years old, never flushed, no error codes, checked manual, cleaned inlet filter (wasn't really dirty), verified vent is clear.

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  • benjaminherr
    benjaminherr Dec 30, 2012

    I found my mistake. I have a hot and cold supply line run together for a outside tap and had opened both up mistakenly so the cold was flowing through this setup and feeding the hot line. I'm flushing the unit now anyhow as I haven't done it yet, but I believe this was my issue/mistake.

  • benjaminherr
    benjaminherr Dec 31, 2012

    Confirmed, that was my mistake.

  • benjaminherr
    benjaminherr Dec 31, 2012

    Issue wasn't with the Rinnai unit, but with me opening an external water tap and allowing cold water to flow into the hot lines after the water heater. I did flush the unit as well, but there doesn't appear to be anything wrong with the heater.

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6 Suggested Answers

6ya6ya
  • 2 Answers

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Posted on Jan 02, 2017

senor8
  • 73 Answers

SOURCE: Rinnai Infinity 26 hot water system set to 55

If you aren't getting any error codes, then the heater is probably doing its job. Your problem is probably somewhere in your plumbing system. The most common reason you get this sort of problem is due to cold water mixing in the hot water system. There are a number of causes for a "cross connection" :

-Faulty check valve
-Missing check valve on reciculation return line
-Faulty shower cartridge
-Thermostatic mixing valve set too low
-Faulty thermostatic mixing valve
-Faulty anti-scald valve

The easiest way to confirm a cross connection is to: 1) shutoff the cold water entering the tankless heater 2) open hot water valves around the house. If you still have water flowing at your hot water fixtures, then you have a cross connection.

Posted on Aug 01, 2010

CRTN
  • 716 Answers

SOURCE: No water flow from hot water tap with a rinnai tankless water hea

Its A Possibility The Left Over Water In The Hot Is Frozen. If Your Line Is Exposed Outside Somewhere It Can Easily Freeze Up. Turn On The Hot Water Everywhere In The House And If Accessible Check The Lines To See Where The Warmth Ends. You Can Leave One Off Over Night In Hopes That It Will Eventually Defrost.

Posted on Jan 16, 2009

  • 6 Answers

SOURCE: vinegar flush

You should not have to flush unless the code LC comes up. but here is the flushing diagram.

Posted on Aug 01, 2009

snap101
  • 117 Answers

SOURCE: Rinnai Tankless won't stay on

how far is the tankless from the gas meter? error code 12 means it doesn't have enough gas running to it. is the 3/4 flex true 3/4 or is it 1/2 with 3/4 threads. have you checked your BTU load on your house to make sure your 1'' pipe can handle everything else you have on the house? sounds like to me you dont have the right amount of gas to the unit.

Posted on Oct 03, 2009

  • 3 Answers

SOURCE: Our Rinnai tankless water heater is producing water as hot as pre

Power outage will reset Rinnai unit to that temperature. Read manual for more info.

Posted on Jan 26, 2010

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