Arrived onsite to customers complaint of no heat, provided options for replacement furnace, and diagnostic work, customer approved diagnostic work. Found that the inducer motor housing was full of water due to condensate trap being plugged. Cleared condensate drain. Next noticed that the furnace was cycling off and on, it was bouncing off of the high limit. Found 14x24x1 filter to be very dirty, swapped with customer supplied filter. High limit switch was still tripping, discovered that it was closing when it was not above its maximum temperature rating. The high limit switch has gone bad. Discovered that the return air duct was 2”x14” this is not adequate return air, and it is causing the internal temperatures to be too high, especially when the filter is dirty. This caused the limit switch to go bad. Found browning marks on control board, these are called hot spots, and are caused by over heating the control board, the cause for this is lack of return air, hot spots on the control bo