Furnace was flashing 3 times when arrived, which is the pressure switch. Checked system and switch. When the inducer is running, it is drawing -.9 to -1.1 in wc of draft. The pressure switch closes at -.65. The inducer works correctly. Jumped out the switch and the burner starts. The pressure switch is closing intermittently and needs to be replaced. Called supplier for availability. Performed a heating pm on a gas furnace. Started and checked the safeties. Cleaned the flame sensor, checked the gasket pressures. Performed a combustion test.