Board says it is a limit switch fault
Furace goes into pre ignition, fan comes on and sometimes even the main burner ignites, but the blower will not come on... is this the blower motor or could this be a switch somewhere?

More than likely your limit switch is faulty, or the sensor is bad in the combustion chamber.

If your furnace lights the main burners but the main fan fails to come on, the limit switch is doing its job by shutting down an over heated furnace. Your fan motor may need a new capacitor (small can with wires to the motor). If it looks swelled up or is leaking it needs to be replaced. It could just be weak. Your motor could be shot, or it could be a blower relay not telling it to come on.