jplante4
You are correct but you also have a leak in your system. Steam systems use water but hot water systems use almost nothing as the system is sealed (except for the air purge valve). I have a boiler and hot water heat. My solution is to install a a large pressure gauge and have my house sitter read it as part of his walk thru. I also have the sitter turn on the water once a week to water house plants and flush the toilets. Doing this allows the auto fill to replenish water to the boiler in case of a small leak.