Rinnai water flow sensor
Part: 100001226
Flow sensor reference for Error 65 after the inlet screen is clean and the turbine still fails to signal flow.
$35-$90
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Rinnai Error Code 65 — Water Flow Rate Fault
Error Code 65 on Rinnai tankless water heaters (V series, RU series, and RL series) means the unit has detected insufficient water flow or a fault with the water flow sensor. Rinnai units require a minimum flow rate to activate the burner and prevent overheating — when flow falls below this threshold, Error 65 is triggered.
Jump to Fix
Minimum Flow Rate for Rinnai
- V75e / V94e / V65e: Minimum activation flow = 0.26 GPM
- RU Series (condensing): Minimum activation flow = 0.26–0.40 GPM depending on model
- Below this flow rate, the unit will not ignite and may display Error 65
Common Causes {#most-likely-cause}
| Cause | Likelihood |
|---|---|
| Clogged inlet filter screen | Very High |
| Partially closed shutoff valve | High |
| Low water pressure at the unit | High |
| Scale or debris in the flow sensor | Medium |
| Failed water flow sensor | Medium |
| Scale-clogged hot water piping or fixture | Medium |
| Recirculation pump issue | Low |
Step-by-Step Diagnosis {#diagnosis}
Step 1 — Check inlet filter screen The most common fix for Error 65:
- Turn off cold water supply to the unit
- Disconnect the cold water inlet connection
- Remove the filter screen (mesh disc inside the inlet)
- Clean with water and a soft brush — replace if torn
- Reinstall and retest
Step 2 — Check water pressure and flow
- Measure cold water pressure at the unit inlet (should be 15–150 psi)
- Partially open fixtures at multiple points to verify flow is reaching the unit
- Check for partially closed shutoff valves at the unit or upstream
Step 3 — Check the flow sensor
- The flow sensor is a hall-effect turbine inside the unit on the water inlet
- Remove and inspect for scale or debris lodged in the turbine wheel
- Clean with water — do not use metal tools on the turbine
- Spin the turbine wheel manually — it should rotate freely with no binding
Step 4 — Test the flow sensor signal
- With power on and water flowing, the flow sensor sends a pulsed signal to the control board
- If the turbine spins freely but Error 65 persists: flow sensor has failed — replace
Step 5 — Check for pipe scale (hot side)
- In high-scale areas, the hot water piping or fixtures can scale internally and restrict flow
- Disconnect the hot water outlet and measure actual flow from the unit
- If flow at the unit is adequate but fixtures are slow: scale is in the distribution piping
Replacement Parts {#parts}
| Part | Notes |
|---|---|
| Flow sensor (water flow rate sensor) | Rinnai part 100001226 or model-specific |
| Inlet filter screen | Rinnai part 100028 or equivalent |
| Flow control valve | Some models have a flow adjustment valve — may need cleaning |
Need Replacement Parts?
Before ordering, match the water-heating part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
Reset Procedure
- Fix the root cause (clean filter, restore flow)
- Press the ON/OFF button to clear the error
- Open a hot water fixture to verify the unit fires at normal flow
- If Error 65 returns: flow sensor is failed
Pro tip: In hard water areas, descale the unit annually and clean the inlet filter every 6 months. A clogged filter is responsible for the majority of Rinnai Error 65 calls.