Bleeding a forced hot water system

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Old 01-30-04, 06:43 PM
lab
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Bleeding a forced hot water system

It would be great if I could get some advice. I have a forced hot water heating system with two zones. It is full of air and does not have bleeders on the baseboards. I have tried to bleed the air from spigots above the zone valves and the spigot right before the circulating pump. I get air out evertime but never all of it. What is the proper way to go about this?? Any info would help a great deal. Thanks.
 
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Old 01-30-04, 08:30 PM
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Turn off the thermostats, close off both zones (there should be two valves per zone), connect a garden hose to one drain valve and open the drain valve. Open the isolation valve to the zone you connected the garden hose to. The valve is the one furthest away from the point where you connected the garden hose. One isolation valve should be below the drain. Not this one.

Now the important part is to also open the water regulator ( small lever is moved to the vertical position). This will allow more flow and higher pressure to fill and push the air out. I find that it is best to have the other end of the hose in a bucket so that it is is below the water surface. If there is any air in the system, you will easily see the air bubbles in the bucket. Just keep this running until all the air is gone (may take 10 minutes or so). Close the isolation valve and drain valve. Swap the garden hose to the other drain. Repeat the above process for the other zone.

You may need to repeat each zone one more time. When done, make sure you set the water pressure regualator arm back. Do this while the garden hose is still connected to an open drain valve.
 
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Old 02-02-04, 05:52 AM
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Ok... quick question about the process above..... Once you turn off power to the boiler and attach the garden hose to the drain valve for that particular zone and open the spickot to let water out thru the garden hose.... do you leave the isolation valve for that zone open or closed?? Last time I bled my system I think I had the isolation valves for all 6 zones closed while bleeding each zone one at a time. Is this correct? Thanks!!
 
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Old 02-02-04, 06:13 PM
lab
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We spent all weekend bleeding these pipes....and they sound just a bad as ever. Is there something else I should check. We got tons of air out of them (and when the bubbles stopped), sealed the system back up and listened. The 2nd floor stayed silent for about a day, the first floor just never got there. Any additional recomendations....other than a plumber?
 
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Old 02-03-04, 07:22 PM
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George2002. there are typically two isolations valves. One is for the water leaving the boiler going to the baseboards and one is after the drain valve on the return loop. You will need to open the valve that leads out to the baseboard. All other valves should be closed.


Lab, are you sure that the system has air in it. I am not sure how you determined that it has air. The sound you hear may be expansion and contraction of the pipe up against wood. If there is air in the system, you will hear water running when the circulator is running. It will be silent (except for the expansion noices - ie ticking, etc) if the pipes have no air.


You just need to make sure that only one loop is open at all times. This will make sure that all the air is pushed out of that loop. You also need to open the inlet feed (regulator) so that it lets more water than the typical 12-15 psi. The water coming out of the garden hose should be pretty fast. Almost as if you had it hooked up to an outside spigot and opend the valve all the way.

The one thing to keep in mind is that since you are putting new water into your heating system, it also bring dissolved air with it. This will all come out of solution over time, but this should easily be taken care of by your autovents and air scoop down at the boiler.

I have successfully done this with baseboard that leads up to a 3rd floor. I would guess that it may take 15 - 30 minutes to completely remove the water out of a zone. I sometimes close the valve and let things settle a bit and then open again.

If you follow the avove steps and see that no more air is coming out of the garden hose, there is no way that air can bet back into the system. If air is getting into the system, then you should also see water getting out of the system there as well.
 
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Old 02-06-04, 12:54 AM
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Bleeding a hot water system

What is the pressure in your system.
Vertically up from your gauge to above the highest rad the pressure needs to be 1 psi for every 2.3 ft. ie if your highest rad is 23ft above the gauge then the pressure in your system should have 10 psi at the gauge plus a small margin. say 2-3 psi, This way the water level will be above the radiator or baseboard or what ever.
If the pump is running at too high speed the suction pressure of the pump MAYBE (I said maybe) dragging in air from valve glands or even joins which don't leak water out but will still allow air to 'sucked' in.
If the pump is too big you will get the same effect and also you can get cavitation,
Normally you should not hear the circulation of water in your system if you do it means you have a problem.
Not enough water in the system or circulation too much.
 
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Old 02-13-04, 04:15 PM
lab
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Thanks for all of the help! It was really air in the pipes (it sounded like a waterfall) but it works great now. We replaced the air scoop on top of the expansion tank and bled the air and everything is fine now. The air scoop was not working properly. Every one was very helpful and I am glad there is somewhere to go like this to get help with this kind of problem. It's easy enough to fix if you have someone will to share the knowledge.

Thank you!
 
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Old 02-14-04, 09:21 AM
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air scoops

caution!!! do not close the cap on the auto air vent, or you will be back to square one! Hopfully you replaced this too, as the are inexpensive.
 
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