Have Lennox Value series with white rodgers 36E gas valve. When thermo calls to run, blower comes on but inightor doesn't lite. It has a Lennos Surelight 4242-C board and the indicator light 1 slow flashes and light 2 is constant on, which the legend indicates primary/secondary limit switch open. I cleaned the flame sensor with steel wool.

Cleaning the flame sensor was good preventive care, but it won't cause a limit switch to reset. Check the air filter, replace if clogged. Typically, limit controls are situated in "hot spots" on the unit, to sense overheating and shut down burner(s) if necessary. Look the unit over for small devices with 2 wires connected and a tiny pushbutton in the center. If you locate any, and the device "clicks" when the button is pressed, that area of the unit is overheating for some reason.