Upon arrival unit was on and running. Upon inspection found that there was a large amount of air in the system causing one of the zones to get air bound and not have heat. Attempted to purge the zones and found that the autofeed was not letting enough pressure into the system to purge all air out. After getting customer authorization we replaced the autofeed backflow combo. Purged most air out of the 4 zones. While purging the air we found the pressure gauge is stuck at 22 and is not moving. Need to return on Wednesday to replace the pressure gauge and finish getting all air out of the system.