If your toilet overflows and damages your floors or ceilings, it may be a covered loss, depending on your deductible amount. However, an instance, or series of instances where your toilet merely runs due to old valves and pumps, extending the cost of your monthly water and sewer bill is not something covered under most ISO property insurance forms.
The only time it is covered is if by the toilet running, it damaged someone elses property. In that case it is called Property Damage. For you broken toilet it is not covered.
Generally, if Water back up coverage is provided in your policy, it should be covered after the deductible is paid. Check the exclusions page of your policy.
A "running toilet" is not typically covered by most homeowners insurance. In fact, even the exploratory digging neeeded to determine foundation leaks is not covered. Actual damage to the structure caused by the leaks would, however, likely be covered. Thus, a ruined rug and the moldy flooring underneath would be covered, but the broken toilet part would not be covered.