Probable causes: 1. Bad safety switch. Boilers are equipped with these all over the place. They can be jumped with a little piece of wire as a bypass. (Don't run a jumped boiler for a long time) 2. Pilot is out. This can happen from backdrafts through your chimney or a bad thermocouple 3. Air in the line. If your heat kicks on and you can hear water swishing around while you're reading in your living room, that's air. Big no no. 4. Bad thermostat. You can test this by taking the cover off and jumping the two connections. If the boiler kicks on, you need a new thermo. Leave the rest to us. Happy shoveling. 😨