Returned to replace pressure switch. Replaced pressure switch, cycled system system still not igniting. Checked and adjusted manifold pressure. Checked all pressure hoses and switches. Checked and verified orifice size. Since system is struggling to ignite, according to Lennox troubleshoot guide system needs a smaller orifice. Tried ordering orifice but nobody has it in stock, checked in warehouse and do not have any in stock either. Ordered part from Lennox riverside, Should be arriving next week. Homeowner was very understanding, but was upset.