Can a municipality force a heritage property owner to keep the building properly maintained?

Yes, generally. Municipalities can require owners of heritage-designated properties to maintain the protected heritage attributes, both through general property standards bylaws that apply to buildings generally and through more specific provisions available under the Ontario Heritage Act aimed at preventing what's sometimes called "demolition by neglect," where an owner lets a designated building deteriorate to the point that repair becomes impractical, effectively achieving the same result as an unauthorized demolition without ever formally seeking approval to demolish it.

Where a municipality believes a designated property is being allowed to deteriorate seriously, it generally has tools to require repairs, and in some circumstances can undertake necessary work itself and recover the cost from the owner if the owner doesn't comply. This reflects the underlying purpose of heritage designation: protecting attributes the municipality has identified as having genuine value, which can't be achieved if an owner is simply allowed to let the building fall apart. Owners of designated properties who are struggling with maintenance costs should raise this with the municipality's heritage staff proactively, since incentive programs or a negotiated approach may be available rather than facing enforcement after deterioration has already occurred.