Confirm the controller layout
Look for Up, Down and On/Off controls on the unit or controller. If your controls do not match, find the performance-data instructions in the manual for your exact model.
Check the unit—not just the faucet
The controller's performance data lets you see what the heater reports at its outlet. That removes much of the uncertainty caused by long pipe runs and fixture mixing when you measure only at a sink.
Before you begin: this is the common sequence shown in several current Rinnai residential manuals, not a universal procedure for every tankless model. If your buttons or display differ, stop and use the manual for your exact model. Do not remove the cover or access internal components.
How to find Rinnai outgoing temperature
Use one steady hot-water draw so the number represents the heater while it is actively producing hot water.
Write down the set temperature
Record the normal setpoint shown on the controller before entering performance data. Do not raise it for this check.
Run one hot-water fixture
Turn on one nearby faucet or shower at a normal, steady hot-water flow. Confirm that the heater is operating, then allow the output to stabilize.
Enter performance-data mode
Press and hold the Down button. After two seconds, keep holding Down and press and hold On/Off at the same time.
Scroll to item 02
Use Up or Down until the display shows 02. In the cited Rinnai manuals, item 02 is Outgoing Temperature °F.
Record the live temperature
Watch item 02 while the water is running. Once the reading settles, record it and compare it with the set temperature from step two.
Exit performance-data mode
Repeat the Down-plus-On/Off combination to return to the normal temperature display. Turn off the fixture when finished.
Make sure you are reading the right number
Rinnai performance mode contains several live measurements. These three are the most useful for this check.
Outgoing temperature
This is the live water temperature reported at the unit's outlet. It is the number to compare with the controller setpoint.
Water flow rate
This is shown in tenths of a gallon per minute on the cited models. A display of 15 represents 1.5 GPM.
Heat-exchanger outlet
This is an internal heat-exchanger reading, not the same measurement as item 02. Do not substitute it for outgoing temperature.
What the result may be telling you
A stable item-02 reading is a useful clue, but it should be interpreted with flow, demand, maintenance history and any error codes.
The heater may be producing normally
If item 02 stays near the selected temperature but one fixture feels cooler, look downstream at pipe loss, a mixing valve or the affected fixture.
Maintenance or diagnosis is worth discussing
If one steady fixture is running and item 02 remains below the setpoint, mineral scale, an inlet-filter restriction, excessive flow or another system issue may be limiting performance.
Flow and capacity may be the clue
If the unit reaches the setpoint with one fixture but falls behind with several, the required flow and temperature rise may exceed the unit's current capacity. That does not automatically prove scale.
A low item-02 reading does not prove the unit needs a flush. It makes overdue maintenance more relevant, especially when performance has declined gradually, but a returning error code, shutdown or sudden loss of hot water deserves proper diagnosis.
Optional: compare the unit with a faucet
At the unit
Record the controller setpoint, item 02 outgoing temperature and—if available—item 01 flow rate while one fixture runs.
At the nearest faucet
Use a liquid-safe digital thermometer in a full-hot stream after it stabilizes. A difference between item 02 and the faucet can point to pipe loss, recirculation or mixing after the heater.
Rinnai Performance-Data Questions
Does every Rinnai use this exact sequence?
Many current Rinnai residential manuals show the same Down-plus-On/Off sequence and identify item 02 as outgoing temperature. Rinnai also warns that performance-data tables can differ by model, so use the exact model manual if your controls or display do not match.
What does item 02 mean?
On the cited Rinnai models, item 02 is the live outgoing water temperature in degrees Fahrenheit.
Is item 11 the same temperature?
No. Item 11 is the heat-exchanger outlet temperature in the cited tables. Use item 02 when you want the unit's reported outgoing water temperature.
Does a low item-02 reading prove I need a flush?
No. Scale or an inlet-filter restriction may contribute, especially when maintenance is overdue, but flow, capacity, mixing, recirculation, sensors or another issue can also cause a lower reading.
How do I leave performance-data mode?
On the cited models, repeat the Down-plus-On/Off button combination. The controller should return to the normal set-temperature display.
Official Rinnai references
The button sequence and performance-data numbers on this page come from Rinnai's published technical information. Always defer to the manual for your exact model.
Tankless service review
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Is the outgoing temperature staying below the setting?
That is a strong sign your tankless water heater is overdue for maintenance.
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