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Rinnai gas water temperature keep alternating from hot to cold

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A fault often found with these units is due to insufficient water flow. Usually this causes specifically the shower to run hot and cold. Try turning on more than one hot supply; if this fixxes the fault you will need to try and increase water flow. Most new tapware/showerware have water flow restictors built in. These are the cause of many problems with continous flow heaters such as the Rinnai. In taps they are usually located in the spout if it unscrews. In showers try the shower hose. Find them and take them out. Also make sure your mains supply to the house is on full.
There are more technical faults but this is something you can easily try first.

Posted on Aug 24, 2010

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Posted on Jan 02, 2017

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We have a problem with our Rinnai 24 hot water service. Hot water goes hot and cold. Does not keep to 38 degrees temperature when showering.


Do You know if there is an anti scald valve in the shower valve? If so it may be scald up with corrosion and need replaced! To see if this could be the problem, flush the toilet next to the shower while the shower is running. If temperature changes in shower I would say that is your problem! If You need to replace it, it would be cheaper to do it yourself! They should be videos on Youtube on how to do it! Good Luck! Regards!

Jul 14, 2017 | Rinnai Water Heaters

1 Answer

In temperature screen at 49 degrees to back to front t's appear and boiler stops


PDF]Operation and Installation Manual Outdoor Tankless Water ...

https://www.rinnai.us/.../U287-1932(00)_Outdoor_...

Rinnai America Corp.Temperature controlled continuous flow gas hot water system. .... This water heaterwill attempt to provide hot water at the temperature setting even when the ...

Hot water system temperatures and the code ' Plumbing ...

plumbingengineer.com/content/hot-water-system-temperatures-and-code
Feb 1, 2015 - There have also been incidents where the circulating pump stopped ...before it connects back to the cold water inlet to the water heater. .... Is there a maximum temperature limit for domestic water heaters? ... a means to limit the maximum setting at the valve to 120°F (49°C) or ... Some do and some don't.

[PDF]User's Operation Manual - contents - Navien


Dec 25, 2015 | Water Heaters

1 Answer

How do I turn it on? I press the "on" button and


The manual says:
http://www.coinwash.com/temp/rinnai.pdf

"For the name of the Authorized Distributor or Installer nearest you, please contact your local HVAC dealer or gas service technician, visit the Rinnai website (www.rinnai.us), call Rinnai at1-800-621-9419 or write to Rinnai, 103 International Drive, Peachtree City, Georgia 30269"

Manual says that the remote is for setting temperature.
When you turn on hot water spigot, tankless water heater will heat the water to the set point temperature.
If water heater is not set up to use remote, then tankless unit will heat to 140 degrees F.
"With the MCC-45-4US remote control installed the water temperature is adjustable from 96
to 180°F. The water temperature cannot be set to a temperature other than 140°F
without the use of the MCC-45-4US remote control unit. If you require a temperature
other than 140°F you must install the MCC-45-4US remote control unit."

"Error messages are displayed on the remote control units, simplifying service calls."

Page 9 of manual shows hot to set temperature using remote.
Water taps must be shut off to set temperature.
Circulating pump must be turned off.
"Simply press the H or C button until desired temperature is displayed"
"green in-use indicator will display"

If your unit is not working, the manual says to contact local plumber.
Fixya has specialists who will talk to you by phone about your problem for a fee.

Dec 18, 2010 | Rinnai Digital Remote Water Heater Control...

1 Answer

When in the shower, the heat fluctuates from hot to lukewarm over a 10 second cycle. The water will not stay at a constant temperature.


this is usually a problem with all tankless water heaters.
the solution is to install a small buffer tank (5 or 10 gallon electric water heater) after the Rinnai. this will give the water something to mix in. it will solve your problem.

did you make sure to use a 3/4" gas line to the unit. not just 3/4" at the unit itself. sometimes when there is not enough gas, the unit will act funny and cycle from hot to warm or even cold. Make sure you check the gas line size, its very important.

Aug 10, 2010 | Rinnai Water Heaters

2 Answers

Exterior mounted Rinnai tankless water heater not


check to see if you have a blocked line on the hot water side

Jan 08, 2010 | Rinnai Webstone The isolator EXP tankless...

1 Answer

Rinnai XR 20 - water temperature varies hot - cold - hot etc during 4 to 5 min shower


your gas supply may be to low to keep the unit firing while you are showering...especially if you have other gas appliances running while you are using the unit.

If this is happening after someone else has recently used the unit....then it may be a problem that some call stacking. The unit works on flow....not sure about that unit but they usually take between 1/2 - 3/4 gallon to turn the burner on. If someone recently used it and then you get in the shower...you will get the hot that is already in the line but then it takes that initial amount to fire again, thus loading the pipe with cold water.....it then comes out on you followed by the hot that has finally entered the line. Once it is past that point there should be no issue, unless it it a gas problem like I mentioned.

Oct 24, 2009 | Rinnai Water Heaters

1 Answer

Fluctuating temperatures


Sounds like there is not enough flow in order to keep the burner in the heater firing continuously

Jul 09, 2009 | Rinnai Webstone The isolator EXP tankless...

3 Answers

I have a Rinnai system. Good cold water pressure, little hot.


What type of pipes are install on this heater?

Mar 13, 2009 | Water Heaters

2 Answers

Runs out of hot water


I wonder if you have this problem below caused by a drop in water pressure from someone flushing a toilet or a washing machine. I would call the company to remedy this issue.

17. What is a cold water sandwich effect? The term “cold water sandwich effect” is a term that is used to describe the introduction of cold water into the hot water supply line during frequent on/off operation of an instantaneous water heater. The cold water sandwich effect, when present, appears as a momentary drop in hot water temperature as it is discharged from a hot water supply outlet (i.e. shower, tub, or faucet). This phenomenon is present in the operation of all instantaneous, tankless style, water heaters, but is minimized with the high tech design of Rinnai water heaters.
The technology built into the Rinnai water heaters is designed to minimize the cold water sandwich effect. Rinnai water heaters are microprocessor controlled and when water flow through them ceases, they remain in a “ready to fire state” for approximately 1 minute. If water flow through a Rinnai water heater begins within the first minute following water flow stoppage, the water heater will fire back up within 1 to 2 seconds. This minimizes the cold water sandwich effect that would otherwise be experienced with a low tech tankless water heater. It should be noted that the cold water sandwich effect cannot be removed completely from tankless style water heaters. The safety standards developed to insure the safe operation of water heaters require a delay in the ignition sequence of all gas water heaters.
While the cold water sandwich effect cannot be completely eliminated from standard plumbing systems, it can be eliminated from plumbing systems that have a supply and return hot water circulating system. Rinnai has developed 2 methods to eliminate the cold water sandwich effect in residential hot water circulating systems.
The first (and preferred) method to remove the cold water sandwich from circulating systems utilizes a small electric tank water heater (powered up) that is used with a dual purpose. The small water heater acts as a mixing tank to eliminate the cold water sandwich effect from the Rinnai water heater and it uses its electric heating element to offset the heat losses from the hot water circulating system.
The second method to remove the cold water sandwich from circulating systems utilizes a small 2 to 6 gallon storage tank installed on the hot water outlet of the Rinnai water heater. This tank acts as a mixing tank to blend the cold water sandwich with hot water and eliminating its effect at fixtures.

Mar 11, 2009 | Rinnai Water Heaters

1 Answer

I have a Rinnai tankless. The temperature fluctuates wildly


I think the dip tube in your water heater has failed, this is a plastic tube that goes in the cold side of your tank and forces incoming cold water to the bottom of the tank allowing hot water out at the top. When this tube deteiorates the incoming cold water mixes at the top of the tank causing the problem you have. the dip tube runs about 5 bucks but takes someone with pluming skills to install.

Jan 05, 2009 | Rinnai Webstone The isolator EXP tankless...

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