Rinnai outlet temperature sensor
Part: Rinnai 100001223
Primary sensor to price first for Error Code 52.
$20-$55
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Rinnai Error Code 52 — Outlet Water Temperature Sensor Fault
Error Code 52 on Rinnai tankless water heaters indicates a fault with the outlet water temperature sensor (also called the outgoing hot water thermistor). The sensor has failed or is reading an out-of-range value, causing the unit to shut down to prevent scalding or heat exchanger damage.
Jump to Fix
Role of the Outlet Temperature Sensor
The outlet temperature sensor monitors the temperature of the water leaving the unit. This is the primary feedback for the modulating burner — if the sensor fails, the unit cannot regulate water temperature and shuts down safely with Error 52.
Rinnai Temperature Sensor Codes
| Code | Sensor | Location |
|---|---|---|
| 52 | Outlet water temperature sensor | Outgoing hot water side |
| 53 | Inlet water temperature sensor | Incoming cold water side |
| 61 | Gas combustion fault | Not a sensor — burner issue |
Common Causes {#most-likely-cause}
| Cause | Likelihood |
|---|---|
| Failed outlet temperature sensor | Very High |
| Corroded or loose sensor connector | High |
| Damaged sensor wire (water damage, pinching) | Medium |
| Control board analog input failure | Low |
Step-by-Step Diagnosis {#diagnosis}
Step 1 — Locate the outlet temperature sensor
- The sensor is mounted on or near the outgoing water connection on the heat exchanger
- It is a small thermistor in a metal probe or clip
- Visually inspect for obvious damage, corrosion, or disconnected wires
Step 2 — Check the wiring connector
- Disconnect and re-seat the sensor connector at the control board
- Inspect for corrosion from condensate or water infiltration
- Clean contacts with electrical contact cleaner
Step 3 — Measure sensor resistance Rinnai outlet temperature sensors are NTC thermistors:
- At 77°F (25°C): typically 10K–15K ohms (model-specific)
- Infinite resistance: sensor is open — replace
- Near-zero resistance: sensor is shorted — replace
- Resistance should decrease as temperature increases
Step 4 — Compare to a reference
- Take the sensor resistance reading and compare to the service manual resistance table
- Hold the sensor in your hand (roughly body temperature, ~98°F) and confirm resistance drops accordingly — confirms the sensor tracks temperature
Step 5 — Check the control board
- If the sensor resistance is correct but Error 52 persists, the board analog input may have failed
- This is uncommon — try a known-good replacement sensor first
Replacement Parts {#parts}
| Part | Notes |
|---|---|
| Outlet temperature sensor | Rinnai part 100001223 or model-specific equivalent |
| Inlet temperature sensor (if confused with 53) | Rinnai part 100001222 |
| Control board | Last resort — verify sensor and wiring first |
Need Replacement Parts?
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Reset Procedure
- Replace the sensor
- Reconnect all wiring
- Press ON/OFF to power cycle the unit
- Error 52 should clear on startup
- Open a hot water fixture and verify stable outlet temperature
Note: Rinnai Error 52 and Error 53 are often confused. Error 52 = outlet (hot water leaving the unit); Error 53 = inlet (cold water entering the unit). Both are fixed the same way — replace the failed sensor.