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Thread: Trouble with one zone and general understanding

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  1. #1
    DIY Junior Member mln's Avatar
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    Default Trouble with one zone and general understanding

    I have an old Weil McClain boiler. It's gas fired but I believe that it's a conversion unit on an oil burner. It has four zones. One of the four zones that heats the upper floor is not heating up. It seems like there might be air in the line as it's warm near the boiler but it cools off a few feet away from the boiler. I can't however understand how to get to the bottom of it and would certainly appreciate some input.

    I have attached a photo. The circulator nearest the camera is the problem. The black valve has a hose bib type connection on it. When the thermostat is off, water flows from here. When the thermostat is on it doesn't flow, just light air. I can't seem to locate any other valves on the line upstairs to allow air out.

    A few more notes. The other zones work fine. The pressure gauge reads zero. The valve for the incoming line off the water main was closed. I opened it today (it's still open) thinking that it would add pressure to the system it didn't seem to have any affect. The thermostat seems to work fine, it clicks on the circulator when switched on. While trying things I opened the valve on the overflow/expansion tank and allowed water to drain for maybe 10 seconds, no idea if this was a bad thing to do.

    Does this sound like air, or maybe something wrong with the circulator??
    Any thoughts are very much appreciated.
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  2. #2
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Quote Originally Posted by mln View Post
    I have an old Weil McClain boiler. It's gas fired but I believe that it's a conversion unit on an oil burner. It has four zones. One of the four zones that heats the upper floor is not heating up. It seems like there might be air in the line as it's warm near the boiler but it cools off a few feet away from the boiler. I can't however understand how to get to the bottom of it and would certainly appreciate some input.

    I have attached a photo. The circulator nearest the camera is the problem. The black valve has a hose bib type connection on it. When the thermostat is off, water flows from here. When the thermostat is on it doesn't flow, just light air. I can't seem to locate any other valves on the line upstairs to allow air out.

    A few more notes. The other zones work fine. The pressure gauge reads zero. The valve for the incoming line off the water main was closed. I opened it today (it's still open) thinking that it would add pressure to the system it didn't seem to have any affect. The thermostat seems to work fine, it clicks on the circulator when switched on. While trying things I opened the valve on the overflow/expansion tank and allowed water to drain for maybe 10 seconds, no idea if this was a bad thing to do.

    Does this sound like air, or maybe something wrong with the circulator??
    Any thoughts are very much appreciated.
    You need to replace your auto feed. If you are getting a zero pressure reading the water is not reaching the 2nd floor. You should be running between 12 & 15 #

    John

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    Retired Defense Industry Engineer jadnashua's Avatar
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    A boiler running at zero pressure is likely to flash boil in the burner...not good. It's sort of like running your car without the pressure cap on the radiator...it can boil over. It could be that your pressure gauge is bad, though. As noted, it should be in that range. With the type of expansion tank you have, you need to turn off the autofill (if you have one, it is either turned off or not working) or fill valve, then drain all of the water out of the expansion tank, then close that valve and turn the water feed on an pressurize the system to the specified pressure. For it to work right, you need to start with the tank empty and the water off. Then close the valve and turn the water on and pressurize the system.

    If you don't have a bleed valve upstairs, it may be very hard to get all of the air out. it does look like you have fairly big circulator pumps, so they may have enough head pressure so that they can overcome an air blockage IF you have the system filled properly (and at zero pressure, you don't).

    Assuming the flow is up from the pump (might not be, but probably you should be able to tell from an indicator arrow on the pump), if you open that valve below it while it is on, you'd have it sucking air...this is not good for a water cooled bearing!

    See what the pros think...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Do not drain the expansion tank. Get the auto feed replaced first. If the auto feed is not working we don't want to drain any more water out of the boiler. You don't have enough water to reach the second floor. Also by trying to remove the air from the system you are only making matters worse. When you open the air vents you are taking more water out of the system and the auto feed is not replacing it. From what I can see of your system it looks like you can purge the system at the boiler which is a much better way for removing the air. But none of this can be done until the auto feed is replaced. I would advise you to get a pro to replace the auto feed as this requires draining the system. Then after refilling he will remove the air for you. If there is air in system no circulator can move the water. They are not real pumps they just create a small difference pressure between the feed and return. Look at the motor most are 1/8 HP.

    John

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    DIY Junior Member mln's Avatar
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    Thank you for the replies, I have a pro coming out in the morning.

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    Pipefitter/Plumber Jon-J's Avatar
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    Sounds like an air issue to me. Are there drains on each side of each zone? If so, turn your boiler off and isolate each zone. Take the zone that is giving you trouble and hook a wash machine hose up to one of the drains on the supply zone. Then take a hose and hook it to the return of the same zone. Take the two open ends of the hose and get a small Waynes make up pump and hook the hose thats going to the supply on the zone to the outlet side of the Waynes pump. Get two five gallon buckets and fill with water.
    Prime the pump and then take put a hose on the inlet side of the pump and put it in one of the full buckets. Take the hose from the drain on the return and then put it in the bucket you are sucking out of with the pump.
    It would helpfull to put ball valves on the pump so you can open and close quickly but if not just turn the pump on and let it dead head off the supply drain if you don't have someone helping. Then.....

    1: Turn the drain valve on the supply

    2: Then open the drain valve on the return

    3: Let the pump circ the new water out of the bucket while it is emptying from the other outlet being careful to keep the return hose under the water so you can see if it is pushing air out of the system.

    4: LEt the pump stay running until you have seen that there is no more air being pushed into the bucket.

    5: Shut the RETURN drain first. Do not shut off the pump yet. After return is shut, then shut off Supply. After supply is shut then turn the pump off.

    As long as your zones have these valves on both supply and return i would repeat the process with all the zones.

    With boiler pressure at zero, open each zone one at a time and monitor the gauge press on boiler. You may have up to 30 PSI on each zone depending what stage you were able to get the valves shut off while flushing each zone. Bleed press off system as needed when opening each zone back up.

    This should bleed all the air out of your system. Run the pressure up to 10-18 psi at boiler. The other thing I would do is get rid of those museum piece pumps and get some in line Grunfos pumps. You will probably pay for them in two years just in the power they save you never mind the maintenance peplacing couplers and whatnot. Going to be a whole lot quieter too.
    Sorry so long.

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