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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.

the new set up recently installed

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Probably still have air in the system.

The circulating pumps on these do not provide much head pressure and cannot overcome significant accumulations of air in any vertical return lines.

If you have baseboard radiators with air bleed valves near the high spots then crack those open to vent until no air and only water comes out (with all zones circulating and also assuming your make-up water connection works correctly). If you do not have the luxury of strategically placed accessible air bleeds then someone will need to properly flush air out by closing the loop across the boiler and flushing line pressure water in one side at high velocity while draining it out the other side across all zones until all the air is purged.

The separate heat/cool thermostats are likely because the original installer did not want to deal with integrating separate boiler and a/c controls into a single thermostat, which would have required slightly more complicated control work than is typical.

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