Ruud Error Code 15: Inlet Temp Sensor Fault
Warning: Your Ruud tankless water heater has detected a problem with its inlet water temperature sensor and has shut down to prevent potential issues. You'll need to troubleshoot or call a technician to get hot water again.
How to Fix Ruud Code 15
- Step 1: Check the display periodically to see if the error clears itself. Sometimes transient electrical noise can cause false errors.
- Step 2: If you are comfortable, check the wiring connections to the water heater. Make sure the power is off. Look for any loose or corroded connections. Do not disassemble anything, just visually inspect.
- Step 3: If the error persists, contact a qualified HVAC technician to diagnose and repair the issue.
How to Reset Ruud Code 15
- Turn off the furnace power switch, usually located on or near the unit.
- Turn off the circuit breaker for the furnace. Wait 30 seconds.
- Restore power at the breaker and flip the furnace switch back on.
- Set the thermostat to call for heat. If the error code returns after 2-3 ignition attempts, the fault requires repair.
What does 15 mean?
The '15' error code on your Ruud tankless water heater indicates a fault with the inlet water temperature sensor. This sensor is responsible for monitoring the temperature of the water entering the unit. The control board uses this information to regulate the burner and ensure proper operation. If the sensor is faulty, the water heater may not be able to accurately control the water temperature, potentially leading to overheating or inefficient operation. Because the unit can't verify safe operation, it locks out until the issue is resolved. This protects the unit from damage and, more importantly, protects you from scalding water.
Affected Models
Replacement Parts
| Part | OEM Number | Est. Cost |
|---|---|---|
| Inlet Water Temperature Sensor | REU6109 | — |
| Control Board | — | — |
Related Codes on Same Models
| Code | Description | Severity |
|---|---|---|
| 11 | No Ignition | Critical |
| 12 | Flame Failure | Critical |
| 13 | Improper Combustion | Critical |
| 14 | Overheat / Thermal Fuse | Critical |
| 16 | Outlet Temp Sensor Fault | Warning |
| 21 | Air Supply / Operational Switch | Warning |
| 24 | Flow Sensor Malfunction | Warning |
| 29 | Condensate Neutralizer Issue | Warning |
| 31 | Inlet Water Filter | Warning |
| 33 | Fan Motor Fault | Warning |