HVACopediaNavien · Tankless water heater
E030 Exhaust overheating
What the control is telling you
Flue temperature went above 149 F (65 C) and the unit shut down.
Applies to: Navien NPE-A2 (built-in recirculation) and NPE-S2 condensing tankless water heaters: NPE-150S2, NPE-180A2/S2, NPE-210A2/S2, NPE-240A2/S2
Likely causes
- Clogged cold water inlet filter
- Scaled heat exchanger
- High return water temperature in recirculation/combi systems
Test and repair steps
- Clean the cold water inlet filter.
- Flush the heat exchanger.
- When this system normally sees return water over 140 F (60 C), you may turn off the exhaust limit: open Installer Menu, then 2. Parameter Settings, then item 6. Exhaust Limit Control, and set Disable. Do this only with CPVC, PP or stainless steel venting, never PVC.
- Warning: with PVC exhaust, leave Exhaust Limit Control enabled (factory default).
- Check Status Information > 9. Exhaust Temp while firing.
- Reset once with the Back button on the front panel and note whether the code returns.
- Code back after a reset? Stay at the unit and phone Navien Technical Support, 1-800-519-8794.
Settings for these units
Installation clearances (indoor / outdoor) · Navien NPE-2
| Side | Indoor | Outdoor |
|---|---|---|
| Top | 9 in. (229 mm) | 36 in. (900 mm) |
| Back | 0.5 in. (13 mm) | 0.5 in. (13 mm) |
| Front | 4 in. (100 mm) | 24 in. (600 mm) |
| Sides | 3 in. (76 mm) | 3 in. (76 mm) |
| Bottom | 12 in. (300 mm) | 12 in. (300 mm) |
Vent clearance to combustibles is 0 in.
Outdoor: use the Navien Outdoor Vent Kit; keep 3 ft from an eave to the top of the vent terminals; mild climates only.
Water quality limits and flushing schedule · Navien NPE-2
| Hardness | grains/gal (mg/L) | Treatment | Flush frequency |
|---|---|---|---|
| Soft | 0-4 (0-60) | None | None |
| Moderately hard | 4-7 (61-120) | None required | Once a year |
| Hard | 7-9 (121-160) | Softener or Navien PeakFlow recommended | Once a year |
| Very hard | 9-12 (161-200) | Softener or PeakFlow highly recommended | Residential once a year; commercial twice a year |
| Extremely hard | >12 (200) | Softener or PeakFlow required | - |
Other max levels: hardness 200 mg/L, chloride 250, copper 1.0, iron 0.3, manganese 0.05, sulfate 250, TDS 500, zinc 5, chlorine 4 mg/L; aluminum 0.05-0.2 mg/L; pH 6.5-8.5.
Flushing is advised when no treatment device is installed; use white vinegar or a tankless descaler.
Models that show this code
7 models in Navien NPE-2
Other codes on the same units
Save it for the next call
Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.
Source: Navien NPE-A2/S2 User's Information Manual (20049624A), 5.2 Understanding Error Codes, p.17. Summarized in our own words; check the original manual for your model.
Homeowner looking at this code? See what it means for you and when to call a technician.
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.