Fresh water carries about 5% air, which would add 1% oxygen to your system to rust the metal parts inside.
The deoxygenated water in the system is now liquid gold, as it can’t be replaced with anything with less oxygen. Also, it is unusual that there is no anti-freeze in the system, so you might be making a very expensive replacement for very good fluid.
If it ain’t broke, don’t fix it.
http://www.HeatProUS.com energy businessmen’s knowledge
Yes, you really have to find out the MAKE and MODEL to get good answers. There IS more than one machine made.