HVACopediaNavien · Tankless water heater
E21 No hot water
What the control is telling you
No hot water
Applies to: Seen on N280
Test and repair steps
- Check the gas
Settings for these units
- Installation clearances (indoor / outdoor) · Navien NPE-2
- Water quality limits and flushing schedule · Navien NPE-2
- Installation clearances (indoor / outdoor) · Navien NPN
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Source: Field report 2026-10-03 by Test User. Summarized in our own words; check the original manual for your model.
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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.