Spark ignition gas boiler. Weil McLain gas boiler. The pilot lights but the boiler doesn't start.

When the pilot lights, does the spark ignition keep sparking, or does it quit? If it keeps sparking even when pilot is lit, you may have a dirty or defective flame senser, or bad ignition control. If the spark quits, but the main burners don't kick in, check for power to the gas valve. Also check all limits to make sure they are closed. What model is your Weil Mclain?

CG-8-PIDN