Posts

All the articles I've posted.

• State Tankless Water Heater E03 Error Code - Causes & Fix

  31 May, 2026

  E03 on State tankless heaters usually signals overheat or low water flow. Check your model manual, clean the inlet filter, and verify flow.

• State Tankless Water Heater E02 Error - Causes & Fix

  31 May, 2026

  E02 means your State tankless heater detected water over the safe temperature limit. Most often the thermistor sensor is faulty.

• Ruud E99 Error Code - Causes & Fix

  31 May, 2026

  E99 on a Ruud tankless water heater means exhaust blower or vent fault. Most often fixed by clearing blocked vents or replacing the blower.

• Ruud Tankless E12 Error Code - Causes & Fix

  31 May, 2026

  E12 is a flame-failure fault: the heater tried to ignite but could not prove a stable flame. Check gas supply and clean the flame rod.

• Ruud E11 Error Code - Causes & Fix

  31 May, 2026

  E11 means ignition failure: the burner won't light or flame isn't detected. Most common fix: clean the flame rod and igniter.

• Ruud E05 Error Code - Causes & Fix

  31 May, 2026

  E05 on a Ruud tankless water heater signals a water flow problem. The most common fix is cleaning the inlet filter screen.

• Ruud E03 Error Code - Causes & Fix

  31 May, 2026

  E03 on a Ruud tankless water heater means overheat shutdown. Usually caused by low water flow or scale buildup in the heat exchanger.

• Ruud E02 Error Code - Causes & Fix

  31 May, 2026

  E02 means high-temperature or overheat fault. The water heater detected unsafe heat and shut down. Lower the setpoint or check sensors.

• Bosch C1 Error Code - Causes & Fix

  31 May, 2026

  C1 means blocked flue or combustion air during startup. Most often caused by obstructed intake/exhaust vent or dirty air filter.

• Bosch E4 Error Code - Causes & Fix

  31 May, 2026

  E4 means backflow temperature over 309°F. Most often caused by blocked venting or a failed secondary fan. Check vent and fan first.

• Bosch E3 Error Code - Causes & Fix

  31 May, 2026

  E3 on Bosch tankless heaters signals a flue gas temperature sensor fault or overheating. Check sensor wiring, test the sensor, or descale.

• Bosch E1 Error Code - Causes & Fix

  31 May, 2026

  E1 means the hot water sensor detected over-temperature (above 185°F). Most often caused by scale buildup or a faulty sensor.

• A.O. Smith E21 Error Code - Causes & Fix

  31 May, 2026

  E21 means a shorted thermistor (TH-1 or T-Out). Most often the sensor itself has failed. Check wiring, then replace the thermistor.

• A.O. Smith Tankless E20 Error - Causes & Fix

  31 May, 2026

  E20 means the inlet thermistor is shorted. The fix is to replace the inlet temperature sensor or check its wiring and connections.

• A.O. Smith E10 Error Code - Causes & Fix

  31 May, 2026

  E10 means the inlet temperature sensor is open. Check the thermistor connection first, then replace the sensor if the code returns.

• A.O. Smith Tankless E06 Error - Causes & Fix

  31 May, 2026

  E06 on an A.O. Smith tankless heater means water temperature is too high. Run a hot tap for 5 minutes to clear the fault or check sensors.

• A.O. Smith Tankless E04 Error - Causes & Fix

  31 May, 2026

  E04 on an A.O. Smith electric tankless water heater means moisture or a leak is detected inside. Turn off power and water, then call support.

• A.O. Smith Tankless E02 Error - Causes & Fix

  31 May, 2026

  E02 means over-temperature: heated water exceeded the limit. Most often caused by low flow or a failing thermistor. Here's how to fix it.

• Rinnai LC Error Code - Causes & Fix

  31 May, 2026

  LC code means scale buildup in the heat exchanger. Flush the unit with descaling solution to clear the code and restore full operation.

• Navien E782 Error Code - Causes & Fix

  31 May, 2026

  E782 means abnormal main panel communication. Usually caused by a failed PCB or loose connector. Check wiring first, replace board if needed.

• Navien E777 Error Code - Causes & Fix

  31 May, 2026

  E777 means abnormal LWCO operation on Navien combi units. Most often it's a loose LWCO wire or low water level on the heating side.

• Navien E740 Error Code - Causes & Fix

  31 May, 2026

  E740 means outdoor temperature sensor failure. Check sensor wiring and outdoor reset configuration, or replace the sensor if damaged.

• Navien E615 Error Code - Causes & Fix

  31 May, 2026

  E615 signals an abnormal control-board or input/memory fault. Most likely fix is to power-cycle the unit and replace the PCB if it returns.

• Navien E594 Error Code - Causes & Fix

  31 May, 2026

  E594 means abnormal EEPROM operation on your Navien tankless heater. The main control board has failed or corrupted memory. Replace the PCB.