HVACopedia

Lennox · Air handler

E312 Reduced airflow - indoor blower cutback

Low severity

What the control is telling you

The blower cannot deliver the requested CFM because of excessive static pressure (design range 0 to 0.8 in. w.c. total external static); runs reduced CFM (dealer information). S30/S40 thermostat alert code 312 (shown as E312 on the unit control display).

Applies to: Lennox communicating air handlers and EIM-equipped indoor units in S30/S40 smart thermostat systems

Likely causes

  • Dirty filter
  • Restrictive or undersized ductwork
  • Closed dampers

Test and repair steps

  1. Measure total external static pressure (cutbacks do not always show an alarm).
  2. Replace the air filter.
  3. Repair or add ductwork.
  4. Clears when the call finishes successfully.

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: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.25. 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.