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Rheem · Furnace troubleshooting

Communicating system not found / no communication

What is going on

RGPE/RGLE: thermostat should show SEARCHING then FURNACE FOUND and AIR CONDITIONER/HEAT PUMP FOUND within 30 minutes.

Likely causes

  • SW4 TERM/BIAS switches not all ON
  • Wire too long or too small
  • Old wire ends
  • Wiring not direct

Check in this order

  1. Make sure all three SW4 dipswitches are ON.
  2. Max wire length thermostat to furnace 100 ft, furnace to condenser 125 ft, 18 AWG minimum.
  3. Wires 1 and 2 should be a twisted pair (green on 1, yellow on 2 recommended).
  4. Trim and re-strip existing wires to expose fresh copper.
  5. Run dedicated 1, 2, R, C wires directly furnace to thermostat and furnace to condenser.

Applies to: Rheem/Ruud (-)GPE upflow/horizontal and (-)GLE downflow 2-stage 80+ communicating gas furnaces

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Source: Rheem RGPE/RGLE Installation Instructions 92-24161-77-02 (ManualsLib 1287511), Communicating systems - wiring and startup, p.49 (PDF p.53). Written in our own words; check the manual for your exact model.

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.