John, circulators and zone valve imply a hot water boiler. Is that what you have?
In a boiler, there are numerous safety monitors. Low pressure, high pressure, over temp, flame sensing, and more if it is a closed system like vacuum caused by the forced induction system. Any one of those safety interlocks could prevent the system from operating.
If you are fairly handy and own either a test light or a multimeter, and can find the wiring diagram, you can isloate what is preventing the system from firing.