Boiler kept shutting down.Re-starts but drops not...

Question

Home heating. I do not have any manual on where to begin troubleshooting but I am able to re-start it It is made by PENNCO (Cast Iron Boilers) with model number: 1504HWD series: 1504HWD serial number P350200053. I could check basic electical connections, open and close valves but will have no idea on what are required running the boiler except for water supply and gas.