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EL01 Indoor / outdoor communication error

High severity Viessmann Vitocal 200-S DLCM(R/H)B multi-zone outdoorViessmann DLFSHB high wall indoor

What the control is telling you

No reply between the indoor and outdoor boards: the indoor unit heard nothing from the outdoor unit for 120 s, or the outdoor heard nothing from an indoor unit for 180 s. Old-style code E1 (48K HH) / outdoor board E2.

Applies to: DLCM(R/H)B multi-zone outdoor units with DLFSHBH high wall indoor units (Midea, Carrier, Viessmann)

Likely causes

  • Wrong or loose L1 / L2 / S wiring
  • Faulty indoor PCB
  • Faulty outdoor main PCB or IPM board
  • Reactor not connected

Test and repair steps

  1. Safety kill power at the disconnect and wait for the inverter capacitors to discharge before touching boards or wiring.
  2. Cycle power at the breaker. If the code clears, watch it for a while.
  3. Check L1, L2, S and ground between outdoor and each indoor terminal block against the diagram. The S wire is polarity sensitive. Use 14/3 stranded with ground, never thermostat wire.
  4. With the unit on, put the red lead on terminal 2 (L2) and black on S (or terminal 3) at the outdoor unit. A healthy line swings back and forth between + and - DC. Stuck positive = outdoor board side. Stuck near zero = indoor side.
  5. Press the outdoor check button (SW1) once: the display shows how many indoor units are talking. Compare with the number installed.
  6. Check the IPM board LEDs and the main board LED are lit, and that the reactor wiring is tight.
  7. Swap parts in this order based on what you found: indoor PCB, IPM board, outdoor main PCB.
  8. In high EMF areas a 14/2 shielded cable can replace L2 and S, shield grounded at the outdoor unit only.

Models that show this code

12 models in Viessmann Vitocal 200-S DLCM(R/H)B multi-zone outdoor, Viessmann DLFSHB high wall indoor

DLCMHBH24CAKDLCMHBH30DAKDLCMHBH36DAKDLCMHBH48EAKDLCMRBH18BAKDLCMRBH36DAKDLCMRBH48EAKDLFSHBH09XAKDLFSHBH12XAJDLFSHBH12XAKDLFSHBH18XAKDLFSHBH24XAK

Other codes on the same units

  • EH31 Indoor external fan over voltage
  • Eh60 Room sensor (T1) fault
  • Eh61 Indoor coil sensor (T2) fault
  • EL0C Refrigerant leak detected
  • F0 Current overload protection
  • F1 Outdoor ambient sensor (T4) fault
  • F2 Condenser coil sensor (T3) fault
  • F3 Discharge sensor (T5) fault

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Source: DLCMRBH/DLCMHBH Multi-Zone Outdoor Service Manual (sold as Midea, Carrier and Viessmann Vitocal 200-S; Viessmann doc 6225551-03, 12/2024), Table 23 Outdoor Unit Error Display p.26; diagnosis p.34-36, 46-48; Carrier MS-DLFSHB-01 High Wall Ductless Service Manual (04/2021), Table 9 p.17, EL01 p.26-27. 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.