Rinnai Tankless Water Heater Error Code 73: Meaning and Fix
Applies to: Rinnai RL75i and RL94i condensing tankless water heaters (Rinnai installation guide U287-1817); the code numbers are shared across Rinnai's range but the steps vary by series.
Reading the tankless water heater display
A tankless water heater shows its fault as a number or letter code on the unit display or on the wired remote controller, and some models keep a short history of past codes. Write the code down exactly as shown before you reset the unit, and check the rating plate for the model number, because the same number can mean different things between series.
Rinnai makes gas tankless water heaters that report faults as two-digit diagnostic codes on the unit or the wired controller. The codes are shared across its range, but troubleshooting steps vary by series, so use the series in your manual. The codes apply to model numbers such as RL75i and RL94i; check the label on your unit to confirm yours.
What causes 73
- Damaged burner sensor wiring
- Failed burner sensor
- Control board circuit fault
How to fix it
If you smell gas, leave the building and call your gas utility from outside; do not touch switches or the unit. Switch the water heater off and let it cool before you touch any internal part, and call a licensed plumber or water heater technician if you are not sure.
The code meaning comes from the manufacturer document listed under Sources. The causes and steps below are general troubleshooting guidance, not the manufacturer's service procedure.
- Switch the water heater off and let it cool before you touch anything inside it. If you smell gas, leave the building and call your gas utility from outside.
- Check the burner sensor wiring for damage or loose connectors.
- Power the unit off and on once to see whether the code clears.
- Leave sensor measurement and board work to a technician.
- If the code returns after these checks, call a licensed plumber or water heater technician and give them the code and the model number from the rating plate.
Questions
What does Rinnai tankless error code 73 mean?
Code 73 on a Rinnai condensing tankless water heater is a burner sensor circuit error.
Can I reset the water heater myself?
Turning the unit off and back on, or unplugging it for about 30 seconds, clears some codes. If the same code comes back, the fault is still there and the unit will shut down again. Do not bypass a safety device to keep it running.
When should I call a technician?
Call a licensed plumber or water heater technician for anything involving gas, venting, the heat exchanger, a thermal fuse or the circuit board, or when the code keeps returning after the simple checks.
Other brands with code 73
The same code can mean something different on another maker's appliance. Check the brand before you act.
Other Rinnai tankless water heater codes
Sources
Part numbers are OEM references; confirm fit by your model number before ordering. Meanings compiled from manufacturer and parts-retailer documentation; see sources below. Unplug the appliance before opening it.
Applies to models including RL75i, RL94i.