HVACopediaNavien · Tankless water heater
E773 Wrong gas type detected
What the control is telling you
The unit detects that the gas connected does not match the gas type set at installation.
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; also Navien NPN non-condensing tankless water heaters: NPN-160U/180U/199U (universal, indoor or outdoor with vent kit) and NPN-120E/160E/180E/199E (outdoor only)
Likely causes
- Wrong gas connected
- Gas type DIP switch 1 wrong
- Unit not converted with the Navien kit
- Measuring tolerance (can trip with correct gas)
Test and repair steps
- Warning: wrong gas causes abnormal combustion and CO - shut the unit down until resolved.
- Check the rating plate against the gas supplied.
- Check front-panel DIP switch 1 OFF = natural gas, ON = propane.
- Make sure any conversion used the Navien conversion kit with the correct orifice.
- Parameter 16. Gas Connect Error Check Enable (default On) controls this check.
- Gas type and DIP setting correct but code still there? 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.
- Installation clearances (indoor / outdoor) · Navien NPN
Models that show this code
14 models in Navien NPE-2, Navien NPN
Other codes on the same units
- E615 Input and memory abnormal
- E736 Cascade communication abnormal
- E740 Outdoor temperature sensor abnormal (with air handler)
- E760 Flushing / service alarm
- E762 Vent pipe not properly inserted
- E782 Main / panel communication abnormal
- E785 Flow switch / sensor abnormal (with air handler)
- E788 Gas type mismatch: DIP switch vs panel setting
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Source: Navien NPE-A2/S2 User's Information Manual (20049624A), 5.2 Understanding Error Codes, p.18; Navien NPE-A2/S2 Installation Manual, 3.3, p.19; Navien NPN-U/NPN-E Installation Manual, 3.3, p.19. 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.