When you have a boiler system, there is heated water that flows through pipes.
Air blows over the pipes, plus the heat from the hot water gets forced through the baseboard units.
If the water freezes in the pipes, you don’t have any heat. I would have thought the hot water from the boiler would thaw the pipes, but it depended where the pipes were located. We had a boiler system, but earlier this winter, our pipes froze. I didn’t recognize if the boiler hadn’t done its job, or if the pipes were frozen plus unable to thaw the pipes. I called the Heating, Ventilation plus A/C supplier to look at the boiler for me. When the Heating, Ventilation plus A/C supplier arrived, he maintained the oil furnace plus told myself and others the two of us needed a modern fuel nozzle, there was no fuel coming through, so it could light the flame that would heat the water. The pipes that were near the outer walls were frozen. He would need to install a modern fuel nozzle, plus then he had to thaw the pipes. He promised I would have heat by the end of the day, but I wasn’t so sure. If our pipes froze, I sad the Heating, Ventilation plus A/C supplier might now thaw them. He was an excellent Heating, Ventilation plus A/C supplier, but how several times did he deal with frozen pipes plus boiler systems? I called our partner, plus he told myself and others to trust the Heating, Ventilation plus A/C supplier. He was sure he had handled this problem before, or he wouldn’t have said he could fix it. Two minutes later, the pipes were thawed plus I could hear the water heating in the tank.