Tankless water heater troubleshooting guides

17 guides. No hot water, temperature swings and flow problems on tankless water heaters. Each one lists the likely causes and what to check, in order.

All brands (2)

• No hot water
  Water runs but never gets hot, and the unit may or may not show an error code.
• Water temperature fluctuates
  Hot water goes hot and cold during use or does not reach the set temperature.

Navien (4)

• Hot water slow to reach fixtures - Navien NPE-2
  Long wait for hot water at the taps.
• Hot water turns cold - Navien NPE-2
  Water from the hot tap is cold or turns cold and stays cold.
• No water from hot tap - Navien NPE-2
  Nothing comes out when a hot water tap is opened.
• Water not hot enough or too hot - Navien NPE-2
  Hot water temperature is lower or higher than expected.

Noritz (9)

• Cleaning ignition and flame rods - Noritz
  Part of annual service and the first check for codes 11 and 12.
• Cleaning the fan and burner - Noritz EZ/NRCR/CDV
  Premix units: a dirty fan or venturi lowers air and gas to the burner (code 90 on older installs).
• Descaling (flushing) the heat exchanger - Noritz
  Periodic descale for hard water. Scale causes 14/16/20/65 codes, unstable temperature, overheated water and clogged filters. A descale takes about 1 h
• Draining to prevent freezing - Noritz EZ/NRCR
  Drain the heater when it will be unpowered or unused in freezing conditions. The unit must stay plugged in for freeze protection.
• Field gas conversion NG to LP - Noritz NRCR/EZ Pro
  Pro units ship for natural gas with the LP kit taped to the top; conversion takes about 5 minutes. Must be done by a qualified installer.
• Heat exchanger replacement - Noritz NRC111 / NCC199
  Service procedure for replacing the stainless (secondary) and/or copper (primary) heat exchanger on NRC111 and NCC199 (N-0841MC / N-0842MC) units. For
• Heater does not fire when hot water is opened - Noritz tankless
  Unit stays off when a faucet is opened, or shuts off after the temperature is changed, with no error code.
• Recirculation not working or hot water slow - Noritz NRCR
  NRCR built-in recirculation does not run, runs at the wrong time, or hot water takes too long.
• Water not hot enough or temperature fluctuates - Noritz tankless
  Customer says water is not hot, swings in temperature, or one fixture is cooler, with no error code. Use the maintenance monitors to split a heater pr

Rinnai (2)

• Checking PC board fuses and thermistors
  How the guide says to test the board fuses and the temperature sensors with a meter.
• Weak or missing flame signal (flame rod checks)
  Electrical checks for a flame rod circuit that reads low, from the Electrical Diagnostics page.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.