Dual Zone....not heating

We have dual zoned heating (thermostat upstairs and one downstairs). To my knowledge, we only have one furnace in the basement, although we do what I think is an air handler in the attic.
Anyway, I just went upstairs and the thermostat is set at 68, but it reads 60. There is no heat. Fan works, but heat will not kick on. Downstairs heat is working just fine and has ran a couple of times in the last hour, just not getting any heat upstairs.Any ideas what could be causing this? Thermostat? something else?