HVACopedia

Navien · Tankless water heater

E438 Circulation pump abnormal (with air handler)

Medium severity Navien NPE-2

What the control is telling you

The circulation pump is not working properly when an air handler (AHU/H2Air) is installed.

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

  • Pump not running or seized
  • External pump not wired to TB1
  • Pump draws more than the PCB output allows

Test and repair steps

  1. Check that the circulation pump runs (manual's listed action).
  2. Run Service menu > 3. Test Mode > 4. Pump (A2) or Ext.Pump (S2): the pump runs 10 s / stops 5 s, 5 times.
  3. External pump wired to TB1 on the PCB with the external pump wire; max 150 W, 1.5 A - use a relay for a bigger pump.
  4. Check the space heating loop for closed valves or air.
  5. Reset once with the Back button on the front panel and note whether the code returns.
  6. Code back after a reset? Stay at the unit and phone Navien Technical Support, 1-800-519-8794.

Settings for these 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.

Open the app

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.