[Trainer]

The need to flush the system is caused by contaminating the fluid in the Aqua Hot coolant tank. Your heater uses regular engine antifreeze. The fluid is never in an engine but it does darken with age.

So flusihing is simply your choice which is not a bad thing but not an urgent process.

Now with the tank drained, the zone pumps will have lost prime. So, once full again, place a radiator pressure tester on the coolant tank, pump it up to 15 psi and turn the pumps on one at a time and watch for coolant to flow through the pex lines. Once primed, they will stay that way.

Glad to hear you are all warm again.