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Navien · Tankless water heater

E434 Water adjustment valve abnormal

Medium severity Navien NPE-2

What the control is telling you

The water flow adjustment valve is not moving or reporting correctly.

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

  • Valve motor or wiring fault
  • Valve stuck (scale)

Test and repair steps

  1. Run Service menu > 3. Test Mode > 2. Water Flow Adjust Valve: the valve drives fully open then closed over about 12 s and shows 0-100%; check the feedback.
  2. Check the valve connector and wiring.
  3. If scale is suspected, clean the inlet filter and flush the heat exchanger.
  4. Reset once with the Back button on the front panel and note whether the code returns.
  5. Fix given 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.