Charging a high-mass solar thermal heating system is much like charging a pressurized system. However, flushing all the air out is more complicated if you're running a combination system: you will need to flush each individual circuit. Always keep at least one circuit open during this procedure.

• If you have a bypass around the hot water heat exchanger, close the ball valve on that bypass half way.
• Close the valve on the shunt loop completely, pushing all flow to the heating system.
• Leave two circuits open and close the others. Allow the air bubbles to exit the system.
• Close those circuits and open the next two. Allow the air bubbles to exit the system. Repeat until all circuits are clear of air.
• Once all the floor circuits are flushed, open the shunt loop and close the floor valve.
• Pump until all the bubbles leave the system.
• Open all the circuits.