was the installer lic,, have ins., did you sign a contract with a warranty? how old is the system? what part of the country are you in? In Texas I use Class 200 pvc for my installs and repairs,and rarley use sch 40 pvc. If you dont feel comfortable with reataching the connection, then i suggest redoing the install with the proper pipe.
Jimmy
Texas Lic. Irrigator
Landscape Irrigation Auditing & Management
Texas Lic. Backflow Tester