What This Error Means

A two-blink code means the furnace pressure switch remains open when the control expects it to close. The furnace cannot confirm the required draft or venting condition.

Symptoms You May Notice

Inducer may run without burner ignition; furnace may repeatedly attempt to start; no heat; code returns during startup; condensate or venting problems may be present on high-efficiency models.

Common Causes

Blocked intake or exhaust vent; water or debris in pressure tubing; cracked, loose, or kinked tubing; blocked condensate trap or drain; weak inducer performance; blocked pressure port; failed pressure switch; wiring fault.

Safe Troubleshooting Steps

1. Turn off furnace power. 2. Check outdoor intake and exhaust terminations for visible snow, ice, nests, or debris. 3. Inspect accessible pressure tubing for obvious kinks, cracks, water, or loose connections. 4. On condensing furnaces, check the external condensate drain for visible blockage or freezing. 5. Do not jumper the pressure switch. 6. A qualified technician should measure draft pressure, inspect the inducer and vent system, and test switch operation against the model-specific specification.

Parts Commonly Involved

Pressure switch; pressure tubing; inducer motor and wheel; intake and exhaust venting; condensate trap and drain; wiring; integrated furnace control.

When to Call a Technician

Recommended if the visible vent openings and drain are clear or if the code returns after one restart.

Safety Notice

Never bypass a pressure switch. It verifies combustion-air and venting conditions that are necessary for safe furnace operation.

Manufacturer Documentation