Furnace will not start; status LED shows 6 red flashes repeating; inducer may run briefly then stop.

Safety first: Turn off power before removing panels or disconnecting hoses. Condensate may contain mild acids; avoid skin and eye contact.

Steps to check:

• Inspect condensate system (condensing models): Locate the condensate trap and drain tubing near the inducer. Remove the trap and flush it with warm water to clear debris. Ensure the drain line slopes continuously downward and is not kinked or frozen.
• Check vent piping: Follow the PVC vent and intake pipes from the furnace to the outside. Look for sags that can collect water, improper joints, or long unsupported runs. Correct obvious sags and ensure hangers support the pipe.
• Monitor pressure switch during run: A technician can connect a manometer to verify that draft pressure remains within the range specified on the pressure switch label. If the switch opens intermittently during operation, it may be weak or the venting may be marginal.
• Replace suspect pressure switch: If all venting and condensate issues are corrected and the switch still cycles open, replace it with the exact Coleman-specified pressure switch for your model.

Because venting and combustion safety are critical, have a licensed HVAC professional verify the installation if this code recurs.