HVAC Code Lookup

Carrier Furnace Code 31

WarningShown as: 3 short flashes, 1 long flash

Pressure switch did not close, or reopened during the cycle. On single-stage furnaces this is the main vent pressure switch; on two-stage furnaces code 31 is the high-heat pressure switch or relay. If the switch stays open longer than 5 minutes the inducer shuts off for 15 minutes before retrying.

Manual wording: “31 PRESSURE SWITCH DID NOT CLOSE OR REOPENED - If open longer than five minutes, inducer shuts off for 15 minutes before retry.”

Documented for: 58SC0A, 58MCB (single-stage); 58MVP, 58UVB high-heat pressure switch (two-stage)

Likely causes, most common first

  1. Restricted vent, or the intake/exhaust pipe blocked by snow, ice, leaves or a nest
  2. Plugged condensate drain
  3. Excessive wind at the vent termination
  4. Disconnected or obstructed pressure tubing
  5. Defective inducer motor or low inducer voltage
  6. Defective or out-of-calibration pressure switch
  7. Improper vent sizing or inadequate combustion air supply

What you can safely check yourself

  • Go outside and check the furnace intake and exhaust pipes for snow, ice, leaves, or a bird/insect nest, and clear anything blocking them
  • Check the condensate drain line and trap for a clog or standing water
  • Check that the air filter is clean

When to call a technician

If the vent pipes are clear and the drain is not clogged, the inducer motor, pressure switch, or tubing needs a technician. Never jumper a pressure switch to make the furnace run.

A Carrier furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.

Sources

Other Carrier codes