Lennox · Furnace / HVAC
3 blinks Pressure switch failed to close
What this code means
The pressure switch that confirms the inducer is drawing exhaust properly isn't closing at startup.
Most likely causes
- Blocked or iced-over vent pipe
- Weak or failing inducer motor
- Condensate line blockage affecting the switch
What to try first
Check the outside vent termination for ice, snow, nests, or debris blocking it.
Safety note: if this code returns after one clean reset, stop resetting it — repeated lockouts usually mean a real fault that needs a licensed technician. Never bypass a safety switch.
FAQ
What does Lennox error code 3 blinks mean?
Pressure switch failed to close. The pressure switch that confirms the inducer is drawing exhaust properly isn't closing at startup.
Can I fix Lennox code 3 blinks myself?
Usually not. Check the outside vent termination for ice, snow, nests, or debris blocking it. If the code returns after one reset, it needs a licensed technician.
What causes Lennox code 3 blinks?
The most common causes are: blocked or iced-over vent pipe; weak or failing inducer motor; condensate line blockage affecting the switch.
Other Lennox furnace codes
All Lennox furnace error codes →
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This information may contain errors or not apply to your exact model — always double-check it against your appliance's own manual before acting. If there's any chance of a gas, fire, electrical, carbon monoxide, or other safety hazard, stop and call a licensed professional or the appropriate agency (e.g. your gas utility) instead of relying on this page alone.