Pilot lit,thermostat on,aquastat and pump working no main heat.

After some research I found that my gas boiler has two sensors,one is called a roll out switch and it shuts off after your boiler over heats due to clogged heat exchange,and the other senses the dampner for position open/closed,well one had a reset tab and presto I have heat. What I learned is clean your boiler every year,you have to take the panels off and reach the heat exchange and brush out and vacuum the soot ,I also used compressed air to blow out between the tubes !