System Corrosion - not an issue
Hydronic system corrosion isn't much of an issue to be concerned with. It happens, and it continues as time go by, but it's really not an issue that we need to be concerned with.
Much of my hydronic heating system is made of iron. The homemade wood stove heat exchangers are all made of iron pipe, the water pump is made of iron, and the hot water filter unit is all made of iron. Many other components are made of unprotected iron, yet I'm not concerned about corrosion.
It's not an issue, and here's why.
Hydronic heating systems are closed loop, so they're not exposed to the air. It's oxygen in the air that supports system corrosion, so as the oxygen is consumed through corrosion, it becomes less and less a concern as a source of corrosion inside the system.
In addition, when water is heated, it drives out the air dissolved within it. Less air in the system means less potential for corrosion. Eventually, the water is deemed to be "dead" as it can no longer act upon system components in a meaningful way.
If the truth be known, the water in the hydronic heating system is always causing corrosion, but as time goes by, the corrosion taking place drops to a rate so small as to be insignificant. Therefore, the use of corrosion inhibitors isn't necessary. We'll all see corrosion inside our systems, but if we keep them buttoned up and operating, it really isn't an issue to be concerned about.
Anytime you open up your system, for whatever reason, you'll be introducing air into the system, and that will start the corrosion cycle all over again, so keep it sealed up unless it's necessary to open it.
Done with System Corrosion, back to Alternative Energy Sources