Question about Rinnai MCC-91-2W Commercial Remote Controller 20K871

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Since installing Rinnai RC80i tankless water heater, the performance of the dishwasher has diminished. The dishes aren't getting clean. I suspect the water temperature is not hot enough. The thermostat is max'd at 120 degrees and by the time hot water gets to the dishwasher, there's probably several degrees of temperature loss. I'm wondering if I should attempt to install the MCC-91-2W Commercial Controller that will enable me to raise the thermostat. However, what about the risk of burns at the showers? In comparison, what's the water temperature at the normal setting on non-digital storage tank water heaters, which is what I had when I wasn't having this problem?

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Follow this steps and fix it. God bless you
Drain a tank:

  1. Shut off power at the electrical service panel and post a sign warning others not to turn it on.
  2. Close the cold-water supply valve and open a hot-water faucet somewhere in the house (to speed draining).
  3. Attach a garden hose to the drain valve and run it outside the house.
  4. Open the drain valve and allow all water to drain out.
  5. To refill the tank, close the drain valve tightly and open the cold-water supply valve. Also open a nearby hot-water faucet. When a steady stream of water flows from that faucet, the tank is full and the faucet can be closed.
  6. Once the tank is full, turn the electrical power back on
Test and replace a heating element:
  1. Turn off power at the electrical service panel and post a sign warning others not to turn it on.
  2. Remove the access panel on the electric water heater.
  3. Disconnect one of the element wires and set a multimeter to RX1000 (resistance times 1,000). Touch one probe to an element mounting bolt and the other to each element terminal screw, in turn. If the tester displays anything but infinity ( open circuit), replace the element.
  4. If necessary, set the multimeter to RX1 and touch the probes to the terminal screws. If there is any resistance reading at all ( closed circuit), then the element is good. If not, replace it. Both upper and lower elements are tested in the same manner.
  5. To remove the element, first drain the heater.
  6. Disconnect the remaining element wire. Remove the mounting bolts holding the element in place. Remove the element.
  7. Replace the heating element with one of the same model, shape, and rating. Make sure you also replace any installation gaskets.
Test and replace a high-limit cutoff:
  1. Disconnect power to the heater at the electrical service panel and post a sign warning others not to turn it on.
  2. Remove the upper access panel and push the reset button.
  3. Replace the access panel and turn the power back on. If the water is hot, the reset was the problem. If not, you'll need to turn the power off again and reopen the access panel.
  4. Use a multimeter to test the cutoff terminals for continuity. If faulty, replace with an exact replacement part.

Posted on Oct 21, 2013

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Posted on Jan 02, 2017

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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

  • 1 Answer

SOURCE: Exterior mounted Rinnai tankless water heater not

What is the outside temperature? If it it is below freezing, you might have a frozen pipe. Using a plumber torch heat up the pipe, if it works, replace the insulation using a heavier layer.

Posted on Apr 04, 2010

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Clean water filter.
Delime heat exchanger.
http://waterheatertimer.org/How-to-delime-tankless-water-heater.html
Add tempering tank to preheat cold incoming water.
http://waterheatertimer.org/Tempering-tank.html
Check for bad single-handled faucet cartridges.
http://waterheatertimer.org/Crossover.html
Don't install multi-sensor computer-chip water heater to water lines and gas line and vent pipe since tankless will develop unsolvable problems.
Contact Rinnai and hear them tell you to call service technician, only to discover there are no qualified service technicians in your area who might be able to solve problem. 1-800-621-9419
Ask why the Rainnai site has much promotional information and no service manuals. Nor does Rinnai offer forum where tankless owners can freely exchange their endless unsolvable problems for all to see.

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Contact manufacturer.
Generally the answer is probably no, especially if you have a family, children, dog and neighbors.

Propane burns Hotter and has more pressure than natural gas.
Burner must be more robust cast iron.
Orifices must be changed to accommodate different gas.
Different gas control valve needed.
In some cases there are dip switch changes for type of gas and altitude above sea level ... the higher the elevation, the hotter gas burns.

Here is expected result from changing NG to LP.
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http://waterheatertimer.org/images/Exploded-house3.jpg

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Bad PC board.
Bad sensor.
Don't buy a tankless because the problems can be endless.

Before blaming the tankless however.
Perform the yearly required maintenance on burner
Delime the unit.
http://waterheatertimer.org/pdf/Bosch_Descaling-heat-exchanger.pdf

Remove and clean aerators, replace low-flow shower heads with large water-wasting shower heads.

IMPORTANT check all your single-handle faucets for crossover.
Water getting cool after 15 minutes could be bad cartridge on another faucet.
http://waterheatertimer.org/Crossover.html
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