Hello all. Sorry for the long winded question but Iím trying to list all of the information Iíve been able to determine. Thanks in advance for any help or comments you can give.

I have a 3-zone hydronic heating system and am having problems with the zone for the top floor. There are 4 baseboard radiators on that floor and only one of them is producing any heat. I have bled the entire system, and rechecked several times, and I believe I have removed all of the air.

On two of the three units that do not produce heat, the open-close valves seem to function normally, the other one seems stuck but it did heat last winter. All of them expel water when I open the bleed valves.

On the bottom floor, where the boiler is, there are three 1 ľ inch pipes that run from the boiler, through the zone valves, and around the periphery of the whole level back to the boiler. Obviously, there are branches off of these pipes for the individual radiators. The one baseboard unit that is producing heat on the top floor is the third of four branches on the loop

When the top floor is calling for heat, the 1 ľ inch pipe that feeds the top floor gets hot all the way around so water is definitely circulating through it.

In the case of one of the branches that is not working, the supply and return pipes run up through a bedroom on the middle floor. When the top floor is calling for heat, the supply pipe slowly gets hot but cools off as it goes higher toward the radiator. The return pipe eventually heats up also and it too cools off as it gets closer to the radiator. I cannot easily access any of the other branch pipes but I cannot feel any warmth in the area of the shutoff valves for the radiators.

I should mention that I had to drain and refill the system twice a couple of weeks ago when I initially bled the system in preparation for the heating season. This was because I had a leaky air vent on the bottom floor. After I drained and refilled the system to replace the vent, I had a leaky drain valve.

Also, the boiler name plate for this 35+ year old sears boiler says it should operate at 30 psi. The gauge is only reading about 22 psi when the burner and circulator are running. Is this the right time to check the gauge? Do I get more pressure by just adding air to the expansion tank with a pump? Could this be the problem?

Thanks!