Responded to no-heat call for 10-year-old LP boiler system displaying ignition fault/lockout. Discovered severely plugged heat exchanger which was cleaned as part of a maintenance kit installation. After cleaning, identified and resolved combustion issues likely caused by either gas mixture changes following recent LP tank filling or previous throttle screw adjustment. Made necessary throttle screw adjustments to properly calibrate combustion on both low and high fire. Verified proper system operation for 20 minutes with stable ignition and performance restored.