Furnace does not run; status LED on Miller control board flashes 2 times repeatedly.

Safety: Turn off power to the furnace before removing panels. Do not bypass the pressure switch for operation; it is a critical safety device.

• Inspect pressure tubing: Locate the round pressure switch near the inducer motor. Remove the rubber tubing and check for water, debris, or kinks. Blow gently through the tubing to clear any blockage and reinstall firmly on both the switch and the inducer port.
• Check vent and drain: On Miller high-efficiency models, ensure the condensate drain trap and hoses are not clogged, as water backup can affect pressure readings. Clear any blockage and verify proper slope.
• Test the switch: With power off, disconnect the wires from the pressure switch and check continuity with a multimeter. A stuck-closed switch will show continuity even with no call for heat or inducer off. Replace the pressure switch if it does not open when at rest.
• Inspect wiring and board: Confirm the pressure switch wires are not shorted together and are connected to the correct terminals on the Miller control board. If the switch tests good but the board still reads it as closed, the control board may be defective and require replacement.