Rheem tankless descaling kit
Use for E16/E61 scale faults after confirming service valves and pump hose fittings.
$35-$110
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Rheem Water Heater Error Codes
Rheem water heaters use different fault signaling methods depending on the type: gas tank models use LED flash codes, electric models use error codes on the EcoNet display, and Rheem tankless models (RTGH, RTEX series) use numbered error codes on a digital panel.
Gas Tank Water Heater — LED Flash Codes
Rheem gas tank water heaters (Performance, Classic, Classic Plus) have a status LED on the gas control valve. Read the flash pattern to diagnose:
| Flash Pattern | Meaning | Fix |
|---|---|---|
| 1 flash (every 3 sec) | Normal operation | None needed |
| 2 flashes | Thermopile voltage low | Clean thermocouple, check gas |
| 3 flashes | Ignition failure | Relight pilot, clean thermocouple |
| 4 flashes | Exceeded temperature limit | Check T&P, water temp setting |
| 5 flashes | Sensor fault | Replace temperature sensor or gas valve |
| 6 flashes | Thermistor fault | Replace gas control valve |
| 7 flashes | Gas valve solenoid fault | Replace gas control valve |
| Continuous on | Power fault | Check voltage to unit |
| No light | No power or pilot out | Restore power, relight pilot |
Fixing 2 Flashes (Low Thermopile Voltage)
The thermopile generates millivolt power from the pilot flame to power the gas valve. Low voltage means:
- Pilot flame too small
- Thermocouple/thermopile dirty or mispositioned in flame
- Old thermopile (replace after 8–10 years)
Clean the thermocouple tip with fine steel wool. Ensure it’s positioned fully in the pilot flame (1/2” into the blue cone). Voltage should read 400–800 mV across the thermopile leads when pilot is lit.
Rheem Tankless Error Codes (RTGH Series)
| Code | Description | Fix |
|---|---|---|
| P1 | No flow detected | Minimum flow not met, check flow sensor |
| E1 | Ignition failure | Gas supply, igniter, flame sensor |
| E3 | Overheat (high limit) | Check flow rate, scale buildup |
| E5 | Fan fault | Verify fan runs, check wiring |
| E7 | Flame sensor fault | Clean or replace sensor |
| E8 | Inlet sensor fault | Replace NTC inlet sensor |
| E9 | Outlet sensor fault | Replace NTC outlet sensor |
| E11 | Communication error | Check wiring between modules |
| E16 | High combustion temp | Descale heat exchanger |
| E29 | Water leak detected | Check connections and flow sensor |
| E61 | Heat exchanger dirty | Descale with citric acid flush |
Descaling (E16, E61) — Most Common Tankless Issue
Scale buildup in the heat exchanger is the primary long-term fault on Rheem tankless units in hard water areas. Symptoms: reduced hot water output, longer heating time, E16/E61 codes.
Descale procedure:
- Close hot and cold service valves at the unit
- Connect a submersible pump and hose to the service ports
- Circulate food-grade citric acid solution (1 cup per gallon of water) for 45–60 minutes
- Flush with clean water for 10 minutes
- Restore water flow and verify operation
Do this annually in hard water areas (over 7 grains per gallon hardness).
Rheem Electric Water Heater — EcoNet Display Codes
Rheem Hybrid Heat Pump and EcoNet electric water heaters use digital codes:
| Code | Meaning |
|---|---|
| E1 | Upper element fault |
| E2 | Lower element fault |
| E3 | Sensor fault |
| E4 | Control board fault |
| LOC | Leak detected (if leak detector installed) |
Technician Tips
Water-heater faults usually point to ignition, flame sensing, venting, water flow, temperature sensors, scale buildup, or control-board inputs. Confirm gas or electrical supply, clean inlet screens, check venting, and descale tankless units before replacing sensors or boards.
DIY vs Pro: Resetting the unit, cleaning inlet screens, confirming water flow, and basic descaling are owner-level checks. Gas pressure adjustment, combustion testing, high-voltage work, and control-board replacement should be handled by a licensed technician.
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.
General Troubleshooting Tips
- No hot water at all: Check gas supply or circuit breaker (electric). Verify pilot is lit on gas models.
- Lukewarm water: Element or burner not firing on demand. Check codes.
- Water too hot: Turn down temperature setting on gas valve or thermostat dial. Max safe is 120°F for residential use.
- Water smells like sulfur: Anode rod depleted. Replace magnesium anode rod.