Am I required to fill the water on my tenants steam heat boilers

[Benjamin Perkins]

Purchased a duplex a few years ago and inherited two longstanding tenants.  The last owner was in his 80s used to stop by once a week and fill the water in the steam boilers. Both tenants expect this to happen as part of part of their rental agreement. It’s not specifically written, just that I have to provide heat. I do not have a lot of free time and would like to put this responsibility on the tenants. It takes an hour of my time and it only takes about 10 seconds for them to do while they are already in the basement doing their laundry. Is this something I am legally required to do?