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mikenri 01-14-2011 09:38 AM

Need advice on bleeding forced hot water heating system
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My heating system has two zones, forced hot water w/ baseboards. I don't know much about heating systems.

In one of my zones, i noticed that the heat recently started not working well, the top pipe in the baseboard gets hot where it enters the baseboard and eventually gets cooler as you move farther away from where it enters the room, the bottom pipe stays cold.

I checked the thermostat and it seems to be working OK.

I also noticed in the zone that is working that i can hear water moving in the pipes when the heat comes on.

I am unsure of the proper way to bleed the system, i see two "hose" valves, one on a pipe coming out of the furnace/boiler, another on the side.

I have attached some images of the two hose valves as well as where it seems the cold water possibly interfaces with the system, any help would be appreciated, this seems like a simple problem to call in a pro for and i just need to purge the air from the lines.

Thank You!

1910NE 01-14-2011 10:16 AM

This may or may not help, but on my system (old cast iron radiators) you bleed each individual unit at the radiator, since air in the system is going to rise up into them. Depending on what type of radiators you have, you might be able to do it that way. There are a lot of variables, depending on the radiators, and how the supply and return lines are plumbed. Have you posted the question over in HVAC? You might get a better response.

mikenri 01-14-2011 10:44 AM

I have baseboards, the hot water goes through the upper pipe in the baseboard, goes all the way around the room, then it's a closed loop going back through the bottom pipe that the fins are around. The portion of the pipe with fins doesn't get warm but the upper pipe does get hot in a portion of the zone, it gradually gets cooler as i move away from where it enters. I didn't see any valves to bleed the system in the baseboard within the problematic zone.

from what i've read these types of systems are bled at the boiler/furnace.

i didn't realize there was a hvac section, i'll try posting there as well.

DexterII 01-14-2011 01:00 PM

I can't see it in your pictures, but at a high spot in the plumbing at your furnace, see if you have an air emitter; a brass cylinder about 4" tall and 3" diameter, with a red cap on top, like an air valve cap on your tires. That red cap should be loose, and there should be no water leaking from it. If the cap is tight, loosen it a turn or two, or, if the device shows water leakage, you will need to replace it. This device should automatically remove the air. Another option is to remove the end covers from some of your units, until you find a vent, which you can loosen with a screwdriver, let the air escape, adn retighten it.

AllanJ 01-14-2011 04:05 PM

The zone control valve for the cold zone may have failed. The system uses either separate circulator pumps, one for for each zone (your picture shows only one, it's green in color) or electrically operated valves, one somewhere in each zone, probably near the furnace.

Does the cold zone work or work better if you shut off the hot zone completely (turn its thermostat all the way down)?

mikenri 01-14-2011 07:29 PM

Thanks for your help and giving me an understanding of how this system works.

Turning the working zone off didn't have any effect on the cold zone.

I found the air emmitter and two zone valves up in the drop ceiling, i tested the valves first by manually setting each of them to open one at a time to figure out what valve controlled the problematic zone.

Sure enough when one of them was manually opened the cold zone got hot, i'll have that faulty zone valve replaced.

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