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Old 11-19-2010, 08:59 AM   #1
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Open Hydronic Heating System... how / need to bleed?


I have an open hydronic heating system in my house. System shares a common stainless steel 80 gallon 188K BTU tank to heat the water along with our domestic H2O supply. From the 2" outlet of the tank, it goes through a 2" spirovent air eliminator, then the 2" pipe continues on to a manifold. Connected to this 2" pipe are six Taco pumps branching off one after the other. These serve each of the heating zones in our home. Each pump feeds through a one way fitting, then connects to a 3/4" PEX distribution line until it reaches each zone's manifold. From each zone manifold pex is reduced down to 1/2". Number of 1/2" lines distrbuted from each zone manifold ranges from two to six. There is a drain valve to connect a garden hoze to just after the spirovent, then just after the return side of the main manifold & just before the water returns to the cold / entry side of the hot water tank.

SYMPTOM: When I turn on the thermostat controlling the first pump in line from the hot water tank, the pump turns on, but water never goes through the PEX leaving it (PEX never gets warm). When I THEN turn on the 2nd pump in line from the hot water tank, I finally do get hot water traveling through the zone on the first pump. However, now I don't get hot water traveling through the 2nd zone. Sure enough, turning on the 3rd pump causes hot water to flow through the 2nd pump. This keeps happening until I get to the last pump. With all five pumps running before it, & when I turn it on, I do get hot water sent through it & on to it's heating zone.

This is a sympton that confuses me and my now various HVAC professionals that have looked at the system. Last winter after bleeding the lines (done by a local HVAC company) the system did work correctly. After sitting for the summer I closed off the cold input into the tank, and flushed thoroughly each of the zones one by one starting with the 6th zone, working back to the 1st. I basically let the home's water main fill the tank and flush water through manifold, through the entire zone, the back to the drain valve just before the cold entry in the hot water tank. I'd then turn the angle cock open leading back to the tank, close the drain valve, turn off that zone's pump, close the tanks cold water input valve, and flush the 5th, then 4th, then 3rd, etc. zone until I completed the 1st zone. I thought during this process I would have been bleeding the system as I went. Only thing I did not do is individually flush each of the 1/2" lines leading from each zone's manifold one at at time... instead I simply flushed all of these 1/2" lines at the same time as I was flushing the entire zone.

What are your throughts? should I bleed the system? Is there another problem?

Thanks in advance for your assistance.

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Old 11-19-2010, 03:51 PM   #2
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Open Hydronic Heating System... how / need to bleed?


Sounds like you may have allowed air to enter the individual loops.

Worse thing you can do to a hydronic system. Is run fresh water through it.

Probably have to bleed each individual pex now.

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