Since the new boiler became "a physical part of" the structure when it was installed, it gets classified as Residential Rental Real Estate and depreciated over 27.5 years with the depreciation for that boiler starting on the date it was placed in service.
Over the past 28 years, the boiler is still on the books with some depreciation left as of last tax year.
Am I to assume this is the old boiler that was replaced with a new boiler in 2020? Am I to further assume that you entered that old boiler as it's own asset 28 years ago? If both assumptions are correct, then that boiler "should" be fully depreciated. (or it will be when you indicate it was removed from service.)
Edit the old boiler and work it through. Select the option to indicate that you stopped using that specific asset in 2020. When asked, enter the date you stopped using it in the rental (which would be the day it broke I presume?) Somewhere in the process of working it through you'll be presented it screen asking "Special Handling Required?" Click YES on that screen. If you click no, then you will be *forced* to enter sales information for that boiler. I seriously doubt you sold a non-functioning asset.
The final screen will show you the depreciation on the old boiler for 2020, up to the time it was removed from service. I fully expect it will show it as being fully depreciated. If that's the case, then you "MUST" leave that old boiler asset on your 2020 tax return so it's reported to the IRS that it's fully depreciated and no longer in use as a rental asset. Then, if that old boiler is transferred into your 2021 tax return *next* *year*, you can just delete it from your 2021 tax return *next* *year*.
