Recommendation needed for heating system repairs

[readsalot.livejournal.com]

So, here I am in my still-fairly-new-to-me house, and I've noticed that the heating system on the second floor doesn't seem to be working. The house has gas heat, baseboard heaters, and 4 zones: first floor, first floor extension, second floor, hot water. All of the zones except for the second floor are getting heat. Can anyone suggest a repair person?