More than likely it isn't the entire valve that needs replacing but just the power unit.
I'm not familiar with the Honeywell zone valves but often you can replace the power unit without even shutting down the system. It could also just be a wiring fault.
Somewhere on your valve there is a manual lever or wheel that will allow you to open the valve manually. Try this and see if you get heat.
Pictures of the valve and also the boiler with its nearby piping might help us to help you.