How do I properly "bleed" the cast iron radiators in a home hot water heat radiation system ?

My home heating system is not operating quite as it should. Not bad, not good. I have one radiator that heats on it's lower half and not the upper half. Another does not heat at all. The first/ground floor radiators in my house seem to work just fine and the two problem radiators are both on the second/upper... show more My home heating system is not operating quite as it should. Not bad, not good. I have one radiator that heats on it's lower half and not the upper half. Another does not heat at all. The first/ground floor radiators in my house seem to work just fine and the two problem radiators are both on the second/upper floor. What's going on here?

When I bleed water from a radiator does the heating system automatically compensate for this by taking in new water?

If the water bleed produces discoloured water does this indicate a problem?

Yes! Go ahead and recommend a website that discusses this particular problem in detail if you would prefer.

Thank You !!
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