Rinnai 65
Rinnai code 65: water flow control fault
Short answer
Code 65 is a fault in the water flow control device, a motorized valve (servo) that limits how much water passes through the heater. Rinnai's steps are to check its wiring, cycle the power, and replace the flow control servo if the code returns.
In this guide
When demand is higher than the burner can handle, a tankless heater restricts the water flow slightly so the water still comes out hot. A small motorized valve, the water flow control servo, does this. Code 65 means that device is not responding correctly.
Rinnai's guide also notes that on units with a bath fill function, code 65 can mean the servo failed to close during bath fill. If that happens, turn off the water and stop using the bath fill feature.
Rinnai makes several generations of tankless heaters (SENSEI, SENSEI RX/CX and older non-SENSEI models). The meaning below comes from Rinnai's own diagnostic code guide; the exact service steps differ slightly between generations.
Common causes
- A failed servo motor
- A loose or damaged wiring harness between the servo and the control board
- Scale or debris binding the valve, especially in hard water areas
What you can do
- Turn the power to the heater off and back on and see whether the code clears.
- Clean the cold water inlet filter, since debris that gets past a torn filter can reach the flow parts.
- If code 65 returns, call a technician.
The usual repair
Rinnai's fix is to replace the water flow control servo after checking its wiring and resistance. It is a mid-priced part, and the job means shutting off gas, water and power and working inside the unit, so it belongs with a licensed installer.
See the full list on our Rinnai error codes page.
Common questions
Does scale cause Rinnai code 65?
It can. Scale and debris can bind moving parts in the water path. Regular descaling and a clean inlet filter reduce the risk.
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Other Rinnai codes
| Code | Meaning |
|---|---|
| 02 | No burner operation during freeze protection |
| 03 | Power interruption during bath fill |
| 05 | Bypass flow control device fault |
| 10 | Air supply, exhaust blockage or condensate trap full |
| 11 | No ignition |
| 12 | Flame failure |
| 14 | Thermal fuse or overheat sensor tripped |
| 15 | Venturi control fault |
| 16 | Outgoing water temperature too high (safety shutdown) |
| 17 | Venturi blockage |
| 19 | Electrical grounding fault |
| 21 | Data transfer error after a control board replacement |
| 25 | Condensate drain clogged or condensate pump error |
| 32 | Outgoing water temperature sensor (thermistor) fault |
| 33 | Heat exchanger temperature sensor (thermistor) fault |
| 34 | Combustion air temperature sensor fault |
| 38 | Exhaust gas temperature sensor fault |
| 41 | Freeze protection sensor fault |
| 51 | Inlet water temperature sensor fault |
| 52 | Gas valve or modulating solenoid valve signal fault |
| 54 | High exhaust gas temperature |
| 57 | Burner overheat switch open |
| 58 | Secondary heat exchanger overheat |
| 61 | Combustion fan motor fault |
| 63 | Recirculation low flow |
| 65 | Water flow control device (servo) fault |
| 70 | Control board (PC board) fault |
| 71 | Gas solenoid valve circuit fault |
| 72 | Flame rod (flame sensing) fault |
| 73 | Burner thermocouple fault |
| 79 | Water leak detected inside the unit |
| LC | Scale buildup in the heat exchanger |
| SS | Service soon (maintenance reminder) |
| FF | Maintenance has been performed (service history marker) |