HVAC Code Lookup

American Standard Furnace: 3 Flashes

Code 3 Flashes: Draft pressure error

Soft lockoutShown as: 3 flashes, pause, repeat

Draft pressure error. The pressure switch that proves the draft inducer is moving flue gas is not in the state the control expects, so the control will not open the gas valve.

Manual wording: “3 Flashes --- Draft Pressure Error - Possible problems: a) Venting problem b) Pressure switch problem c) Inducer problem”

Documented for: *UD1 / *DD1 and CUB1 / CDB1 fan-assisted gas furnaces with the LED-only integrated furnace control

Likely causes, most common first

  1. Venting problem
  2. Pressure switch problem
  3. Inducer problem
  4. Excessive combustion vent pressure or flue blockage
  5. Induced draft blower failure - if pressure is not sensed by the pressure switch it will not allow the gas valve to open, therefore the unit will not start

What you can safely check yourself

  • Look for blockage - check whether snow, ice, weeds, grass, leaves, or a nest is blocking the furnace venting outside
  • On a 90%+ condensing model, check the condensate drain line and trap for a clog and check that any condensate pump is working
  • Make sure the furnace door is on properly

When to call a technician

If the venting is clear, the pressure switch, its tubing, or the inducer motor needs a technician. Never jumper or bypass a pressure switch.

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

Sources

Full page for American Standard code 3 Flashes

Other American Standard codes