The single speed flo center circ pump failed. It is on a 31 year old "loop pump kit" LPK from Command Aire Geo HP 2 ton closed loop pressurized system. While give great info on variable speed pumps - am opting to not temp fate and use OEM replacement. The local HVAC guy will install, but no Geo experience. So some back up advice helpful. The loop has no manifolds - headers on system outside. One income pipe/one outgoing. Flo center - incoming into an air expansion that goes into the circ pump and from pump directly to Geo unit. The circ pump has an isolation valve on each side of pump. I know that the two isolation valves are shut off and only pump motor and impeller installed - not entire pump. Q: How do you get pump filled and air out without pushing air into loop? I would think opening one isolation valve with screw open until fluid comes through - but it appears that Grundflos is saying NOT to use pump to bleed system. Q: LPK says to use one of the opened isolation valves to adjust loop pressure back to 40 psi. What and where would the HVAC guy do that? Would it be done on Petes of both incoming AND outgoing loop pipe connections at HP? Anyone have experience with these really old geo systems?