Recommendations vary dramatically, but it is worth checking a boiler's water level frequently, cleaning parts of the unit monthly and having the unit thoroughly clean at least once a year. Safety relief valves and other parts should be checked once every few weeks.
Boiler specifications differ by brand and model, so homeowners should follow recommended guidelines to ensure the longevity of their investment. Maintenance schedules for commercial and residential units also differ; since homeowners are rarely HVAC experts, residential units are designed to work well even if neglected for lengthy periods of time. Large commercial and industrial units, on the other hand, often favor slightly better efficiency even if it means more frequent maintenance is required. Many manufacturers recommend near-daily cleaning on some of their especially large units.