HeatingCodesTankless water heater no hot water in cold weather: what to check
Step 1: Read the code
Look at the display. Then use the matching table: Rinnai, Rheem or Navien. The same number can mean different things by brand.
| Symptom or code | What the manual says | Page |
|---|---|---|
| Rinnai code 10 | A clogged or frozen condensate line backs up into the condensate trap and shuts the heater off (SENSEI and SENSEI RX/CX models) | Rinnai 10 |
| Navien E110 | Abnormal air pressure: ensure the vent pipe is free of obstructions | Navien E110 |
| Rinnai 11, Rheem 11, Navien E003 | No ignition or flame not detected: gas valve open, propane in tank, gas type setting, venting | Rinnai 11, Rheem 11, Navien E003 |
Navien's freeze-protection guidance
- Do not unplug the power supply cord except for routine maintenance. The freeze protection function needs electricity and runs as long as the electric supply is connected, whether or not the unit is switched on.
- Do not close the gas valve except for routine maintenance, as this limits additional freeze protection.
- If power or gas must be disconnected for an extended period, drain the water heater, because freezing damage may occur if there is a loss of power or an interruption in the gas supply.
- Navien strongly recommends a direct vent exhaust and intake system and says the optional recirculation mode is intended for freeze protection.
- The unit should not be installed outdoors in areas prone to freezing temperatures.
- Freezing damage is not covered by the Navien limited warranty.
If you suspect the unit is frozen
Navien's manual gives these steps for a unit you believe is frozen: press the Power button to turn the water heater off; close the gas valve; open the hot water faucet nearest the water heater; and warm the primary and secondary heat exchangers with a hair dryer or a portable electric heater. It then says to check every few minutes for water flowing at the faucet, and once water flows, check the unit and piping for leaks. If you detect leaks or the unit is not operating properly, contact an authorized technician or licensed professional.
A note on scope
The freeze-protection steps above come from the Navien NPN manual. Other Navien models and other brands have their own instructions, so check your owner's manual before applying them.
Frequently asked questions
Why does my tankless heater stop in freezing weather?
The manufacturer documents list a frozen condensate line, a vent or intake blocked by snow or ice, a gas supply interruption or a frozen heat exchanger or pipe. The display code helps tell which.
Should I turn off my tankless water heater during a cold snap?
Navien's manual says to keep the power connected and the gas valve open, because the freeze protection feature depends on both. Draining the unit is recommended when power or gas will be disconnected for an extended period.
Sources
- User's Information Manual: NPN Non-Condensing Water Heaters, section 5.2 Understanding Error Codes (Navien) Covers: Navien NPN-series non-condensing tankless water heaters (NPN-120E through NPN-199U). Condensing NPE/NCB models have their own manuals.
- Troubleshooting Tankless Water Heater Diagnostic Codes (Rinnai America) Covers: Rinnai tankless water heaters in the SENSEI, SENSEI RX/CX and non-SENSEI series. Not every code applies to every model.
- High and Super High Efficiency Tankless Water Heater Troubleshooting Manual (AP21822 Rev 02) (Rheem) Covers: Rheem high and super high efficiency tankless water heaters (condensing and non-condensing, indoor and outdoor) covered by this manual.
Safety note: this page is general information drawn from the sources above. Gas, combustion and line-voltage repairs belong to a licensed professional. Your own equipment's label and manual take priority over anything here. Read the full disclaimer.