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Carrier · Heat pump

16 Lost communication with user interface

Medium severity Carrier 2-stage 24ANB/25HNBCarrier single-stage communicating HP

What the control is telling you

Amber STATUS light flashes 16: the outdoor board no longer hears the Infinity user interface.

Applies to: Carrier 25HNB6/25HNB9 two-stage HP; single-stage communicating HP

Likely causes

  • Loose or broken ABCD wiring
  • Wiring fault at indoor unit or UI
  • UI or indoor unit without power

Test and repair steps

  1. Check the A, B, C, D connections at the UI, indoor unit and outdoor board.
  2. Confirm 24 V between C and D at the outdoor unit.
  3. Look at the green COMM LED it should be on steady once messages are received.
  4. After 2 min without messages the board returns to standby.

Models that show this code

8 models in Carrier 2-stage 24ANB/25HNB, Carrier single-stage communicating HP

25HNB62425HNB63625HNB64825HNB66025HNB92425HNB93625HNB94825HNB960

Other codes on the same units

  • 25 Invalid model plug / inverter size
  • 31 High pressure switch open
  • 32 Low pressure trip
  • 45 Outdoor control board failure
  • 46 Brownout
  • 47 No 230 V at unit
  • 53 Outdoor air temperature sensor fault
  • 55 Outdoor coil temperature sensor fault

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Source: Carrier Residential AC & HP Application Guideline and Service Manual 24-25-9SM (text export), Table 14 Status Codes / Table 18 Troubleshooting. 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.