Thank you all for the advice. Here's how the problem was resolved... (Sorry for my lack of knowledge and correct jargon) For the second floor heat (in our 45yr old+ house), apparently there is one loop of piping and each radiator has a supply and return coming off this loop. The hvac person installed valves (in the basement)on the supply and return "T's" of the problem radiator and also replaced the circulator pump with a variable speed circulator (so that he could push more water through). With the valves, he was able to shut off the flow to each end of the radiator (1 at a time)and was finally able to get the air out. He said the supply line is connected to the end of the radiator DISTAL from the bleeder valve - but that it doesn't matter...since it is a complete loop. This doesn't really make sense to me... but the heat is working now. By the way he said that he connected the radiator as it was before, and it must have been like this all along...??? So, hopefully my problem is solved, and we will not have constant problems with this radiator...???

The outflow pipe from the water heater is warm just above the heater, so it is heating, but the rest of the pipe (6-10 ft) to the cirulating pump is cool to the touch. The pumps themselves were almost too hot to touch, and the pipe just beyond them was also very warm. I could feel some vibration so it appeared the pumps were running. We have now turned the system off and everything is cool (except right at the water heater). Could there be a vapor lock or something like that where the pumps are working hard and heating up but the water isn't circulating?

If you have a lot of pipe and it takes time to hot water to the faucet they are worth it. They are used mainley in buildings so instant hot water is available. You can install an aquastat in the line, possibly at the end and wire it in to your circulator. For example, set the aquastst at 130deg. When there is 130deg in the line it will shut the pump down. When the water in the line cools it will activate the pump to reheat the water.

You've probably never been in a home with properly sized ductwork. Don't feel bad, it's estimated that as much as 3/4 of the heating and cooling systems in the US are oversized. 2 stage and modulating furnaces are better, but I've lived in a home with both, and both can be very comfortable and the single stage equipment doesn't make it feel more dry that I can tell. BUt you are correct, multistage cna reduce the sense of dryness you might get with a less than ideal system. THe RH of hot air is lower than cooler air, but cool air can make things feel drafty. That's why radiant heat is popular. You essentially have very, very low air velocities and much of the heat energy is indirect infrared heat which make you feel warmer, similar to direct sunlight. Keep in mind too, that unless you have an outdoor rest control for hte boiler or to sped up or slow the circulator, most hydronic air handlers are single stage for heating. So the heat is no different than a furnace. Worse, as you reduce BTU's to the coil, the airflow speed is usually ocnstant, so air temps get cooler. My point being, that a properly designed and installed furnace won;t make it feel dry even if single stage. But yes, oversized furnaces and those with restricted airflow can. Vairble capacity will always make the system more comfortable, but it will cost more. Radiant heat overall is superior, but the installed cost is much, much higher. That's why it fell out of favor. Same reason drywall took over the market and plaster disapeared. ITs' primarily a matter of cost. It's also why stone and brick homes aren't built anymore and concrete homes are the minority.