I need to move one of those under the counter heaters in my kitchen. It is attached to my forced hot water heating system. What should i do to drain the system and make sure that it doesn't fill itself while I am moving the heater? Kill power to the heater and turn off new water feed to heater. Is there an easy way to drain the hot water system? Once I turn it back on will it purge the air or do I need to do something.