The other day, my heating guy removed our old system (completely) and installed a new system (Weil Mclain Gas-Fired Water Boiler) along with a new water tank. He said we didn't need all these 'elbows' on the new system and he wanted to redo everything. He's passionate about his work. Last week one zone stopped working. He fixed it by letting some air out. Then another zone wouldn't work and he fixed it. Now the same second zone isn't working.
The home has 2 zones top floor / lower floor. Upstairs has a control unit just for heat and another just for A/C. They are seperate thermostats. Same for the first floor. One unit for A/C, and one unit for heat. This is just how the builder did it many years ago. There might be some reasons for this but I am not entirely sure as to why. Big home? 120 ft long?
When the HVAC guy was hooking up the thermostats to test out the system he was caught off guard when he noticed we had 4 thermostat controllers providing for two zones.
Here's a photo of new setup.