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Rheem · Furnace troubleshooting

Furnace short cycles or does not hold setpoint

What is going on

Heat cycles end early or room temperature drifts.

Likely causes

  • Thermostat badly located
  • Heat anticipator setting
  • Limit opening and closing on low airflow
  • Furnace oversized

Check in this order

  1. Check thermostat location away from registers, sunlight, pipes/wires in walls.
  2. Check heat anticipator setting; an isolation relay may be needed.
  3. Check if a limit is cycling (code 22) filter, ducts, blower speed, temperature rise.
  4. Verify furnace size against load.

Applies to: (-)802PA050314MSA, (-)802PA075417MSA, (-)802PA100521MSA, (-)802PA125524MSA, (-)802PA150524MSA and matching (-)(-)80MDP models

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Source: Rheem (-)802P/(-)(-)80MDP Installation Instructions 92-24161-146-02, Diagnostics Flowchart (Figure 33), p.51. 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.