A hot water heating system doesn’t require a great deal of maintenance. Examine the type of circulator you have, to know if it requires a few drops of oil once per year or none at all. Look at the pressure gauge on the boiler to see any sudden pressure drops that would indicate a leak. Do not change the water in the system as it has already been deoxygenated through use to prevent oxygen corrosion. Have the boiler checked and serviced by an experienced heating plumber at least once per year.