cold radiator


  #1  
Old 12-05-04, 11:03 AM
lomay
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cold radiator

I have a new house with wall panel radiators (Myson). There is a 1st floor zone and second floor zone in a reverse return system. Zone valves with a single circulator are used for a total of 2000sf heated space.

Here is the problem that the plumber can't resolve.

The next to last radiator on the second floor develops air locks. When I bleed the problematic radiator, SOMETIMES the hot water comes into it from the return rather than the supply. Also, I notice when the circulator shuts off, I hear a sound in the system like when you turn the water on hard and it resonates thru the piping.

All radiators are at the same elevation except for the last radiator which is mounted 8" lower than the others. Between the problematic radiator and the last, the supply and return mains jump up over a beam and down again into the floor plenum, an offset of about 5".

It appears that that a pressure imbalance may cause the inflow thru the return, however that may be a result of the airlock. It also appears in that one radiator only, when I bleed it the pressure in the water stream is weaker than any other radiator in the house.

My thinking is if I but a valve in the supply main between the last 2 radiators and partially close it, it will force more water into the problematic radiator and force the air that collects there back to the boiler room where the air separator can remove it. Secondarily, I can put an automatic air vent on that problematic radiator to bleed it on a constant basis.

I can't understand why the problem is confined to that one radiator. Also, Why would the air locking be continuing months after the system was activated. Presumably the air separator and vent are removing any released air and it shouldn't be collecting in the radiator. I've considered also that air could be getting into the system but I don't think that is possible. We air pressure tested it before filling and there are no signs of leaks nor are there pressure drops indicated on the temp/pressure gage form one week to the next

Insight will be greatly appreciated.
 
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Old 12-05-04, 03:27 PM
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The ups and downs are not allowed. The pipes will do it but unless it is a continuous loop, there is no way to force water through that problem radiators. You can't purge unless you can isolate the other radiators. I just did one today where there were four radiators in the basement and one would not circulate. It was probably a small air trap in that particular radiator loop so I isolated (lucky they had valves) the others and purged some water through. It heated immediately and continued to work after the others were opened up again. You need to do the same thing. If you can close off every other radiator on that loop and purge some water through, you will probably have it licked. There is no other way except to find the airlocked piece of pipe and put a bleeder on it. The noise you hear when the pump stops is the air that is being pulled toward the radiator going back to the high point. Sometimes increasing the system pressure during the bleeding purging process can be helpful because it makes the air pocket smaller and it increases water velocity in the pipes when you purge.

Ken
 
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Old 12-05-04, 05:22 PM
lomay
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Cold radiator

Ken,

WThanks for the response.

I am able to bleed the cold rdiator and get it to work, sometimes for a day sometimes for several, but it eventually locks up again. So purging it is not a problem, Also, the noise I hear is not localized to the problematic radiator, it comes I think fom the boiler area though I haven't heard it when I've been next to it.

Also, please explain further what you mean by "The pipes will do it but unless it is a continuous loop, there is no way to force water through that problem radiators. " It fact the pipes are a continuus loop.
 
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Old 12-05-04, 05:40 PM
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The pipes can be run any way one chooses to run them but if you can't get the air out of them they were poorly installed. I think you have more air in the system than you think. Usually when hot water seems to go back up the return it is because the circulator stops and the pressure differential is gone. Then the hot water in the boiler goes back to equalize the pressure. What kind of deaerator is installed on your system.

Are you saying that after you bleed the radiator, the loop circulates normally for a few days? After that what happens? If you have only one cold radiator, they can't all be on a series loop. They must be parallelled on a loop. Unless I am not understanding your system yet.

Ken
 
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Old 12-05-04, 05:55 PM
lomay
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cold radiator

The hor water isn't going thru the reurn system wide, only on the branch to the prblematic radiator. There is a flow control valve on the return main where it ties back into the boiler. The problem is definitely a local one, that is it only affects that one radiator.

After I bleed the radiator the loop operates naramally for a few days or sometimes maybe only a day. The radiators are not in a series loop.

As for understanding the system, this is a 2 pipe reverse return system. Basically, I have a supply main and a return main. Each radiator is on a short loop off the main.

The 1st radiator off the supply main is the last in line to return, that is, the return main follows the supply main. The 1st radiator has the shortest pipe run from the boiler via the supply main and longest pipe run via the return main back to the boiler. The last radiator has the longest pipe run pipe run from the boiler via the supply main and shortest pipe run via the return main back to the boiler.
 
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Old 12-05-04, 06:01 PM
lomay
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cold radiator

It also occurs to me that the sidearm water heater has no purge valve on it's loop. Is it customary to have one. This could account for the additional air that seems to crop up after the radiators have been purged. Since the circulator to the sidearm probably wasn't running when the system was purged or repurged, its trapped air eventually may have been pumped thru and ended up back in the heat loop. The hot water heater piping definately gurgles when its circulator comes on. Still, I would think the air separator would eliminate this.

The air separator is an Amtrol air scoop.
 
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Old 12-05-04, 06:19 PM
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Without actually trying to sound biased, I have no use for the Amtrol Air Scoop. It is rarely installed properly and when it is, it is marginally effective. How much straight horizontal pipe leads to the air scoop without any elbows? Spirovent and Honeywell sell very effective deaerators. The reverse return is the best type of 2 pipe system. There should always be an equal pressure across all radiators. However, if you have air in one and can't get rid of it, you see the result. Once you get all that air out, or at least 90% of it, things will be OK until you need to drain it again. Where is the circulator mounted? If it is on the supply side of the boiler, you won't need a purge valve on the indirect tank.

Ken
 
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Old 12-05-04, 06:31 PM
lomay
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Cold radiator

I've considered that the problem may be an ineffective scoop. There are about 10" either side of the scoop befoore the pipe 90's.

The heat loop circulator is mounted just after the scoop and expansion tank. The sidearm circulator T's off of the the boiler out line before the expansion scoop and expansion tank. So while that sidearm water isn't de-aired like the heat loop water, it all is part of the same connected piping system so eventually it does get routed thru the scoop. So am I corrct in understnding with this setup no purge valve is required for the sidearm loop?
 
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Old 12-05-04, 06:42 PM
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10" is getting close to what is needed to make an air scoop work its best. I have the feeling you have air that is out there somewhere and has yet to be removed. I don't think you will get a whole lot of air past that scoop. Not enough to make a radiator go airbound. Do you have valves on the individual radiators? Do you have the valves necessary to purge the main loop?

Ken
 
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Old 12-05-04, 07:53 PM
lomay
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cold radiator

Each radiator has a purge valve. There is a master purge valve at the boiler where I can purge the primary outflow before it splits off into the zone loops. I would think if the separator is working properly, purging dialy or every few days at the problematic raditor would have removed any residual air.

What is the optimim horizaontal pipe length either side of the separator. I believe I've read somewhere that it should be 12"
 
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Old 12-05-04, 08:13 PM
lomay
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cold radiator

I checked the distance from the separator to the centerline of the 90 and it is actually about 5"
 
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Old 12-06-04, 05:20 AM
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If you are planning on moving it, just remove it and put in a Spirovent or equivalent. You can still put your expansion tank in the bottom of it and it will take out all air and does not need any special installation. I think the air scoop should have at least 16" but the more the better. That only pertains to the inlet, the outlet does not matter.

Ken
 
 

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