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Navien · Tankless water heater

E110 Abnormal air pressure

High severity Navien NPE-2

What the control is telling you

The air pressure sensor (APS) detected a blocked or restricted air path.

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 air intake filter
  • Blocked exhaust or intake (debris, snow, ice, nests)
  • Vent run too long or too many elbows

Test and repair steps

  1. Make sure the exhaust pipe and termination are clear (manual's listed action).
  2. Clean the air intake filter (the manual says a clogged filter causes Error 110).
  3. Check vent length max 75 ft with 2 in. (6 elbows), 150 ft with 3 in. or 4 in. (8 elbows); subtract 8 ft per 90 deg elbow on 2 in., 5 ft on 3 in. or 4 in.
  4. Make sure terminations are at least 12 in. above the highest expected snow line.
  5. Check Status Information > 14. Current APS (APS voltage).
  6. Reset once with the Back button on the front panel and note whether the code returns.
  7. Code back after a reset? Stay at the unit and phone Navien Technical Support, 1-800-519-8794.

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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.