No heat on most of top floor zone

Discussion in 'Boiler Forum' started by atelsth, Oct 19, 2009.

  1. atelsth

    atelsth New Member

    Messages:
    16
    Hello all. Sorry for the long winded question but I’m trying to list all of the information I’ve been able to determine. Thanks in advance for any help or comments you can give.

    I have a 3-zone hydronic heating system and am having problems with the zone for the top floor. There are 4 baseboard radiators on that floor and only one of them is producing any heat. I have bled the entire system, and rechecked several times, and I believe I have removed all of the air.

    On two of the three units that do not produce heat, the open-close valves seem to function normally, the other one seems stuck but it did heat last winter. All of them expel water when I open the bleed valves.

    On the bottom floor, where the boiler is, there are three 1 ¼ inch pipes that run from the boiler, through the zone valves, and around the periphery of the whole level back to the boiler. Obviously, there are branches off of these pipes for the individual radiators. The one baseboard unit that is producing heat on the top floor is the third of four branches on the loop

    When the top floor is calling for heat, the 1 ¼ inch pipe that feeds the top floor gets hot all the way around so water is definitely circulating through it.

    In the case of one of the branches that is not working, the supply and return pipes run up through a bedroom on the middle floor. When the top floor is calling for heat, the supply pipe slowly gets hot but cools off as it goes higher toward the radiator. The return pipe eventually heats up also and it too cools off as it gets closer to the radiator. I cannot easily access any of the other branch pipes but I cannot feel any warmth in the area of the shutoff valves for the radiators.

    I should mention that I had to drain and refill the system twice a couple of weeks ago when I initially bled the system in preparation for the heating season. This was because I had a leaky air vent on the bottom floor. After I drained and refilled the system to replace the vent, I had a leaky drain valve.

    Also, the boiler name plate for this 35+ year old sears boiler says it should operate at 30 psi. The gauge is only reading about 22 psi when the burner and circulator are running. Is this the right time to check the gauge? Do I get more pressure by just adding air to the expansion tank with a pump? Could this be the problem?

    Thanks!
  2. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    You still have air in the system somewhere.
  3. atelsth

    atelsth New Member

    Messages:
    16
    So the air must be in the 3 baseboard units that are not heating? I've bled them all and I get nothing but water. How long should it take before I get air out of a 7 fot long baseboard unit?

    Thanks
  4. atelsth

    atelsth New Member

    Messages:
    16
    I was able to get some air out of the baseboards by elevating one end of them. It took more than 3 cups of bleeding before I got warm water out of the bleeder.

    However, the water only flows when the bleeder valve is open. The pipe never gets hot downstream from the bleeder valve??
  5. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    How many feet from the boiler to the radiation on the "top floor"?
  6. atelsth

    atelsth New Member

    Messages:
    16
    Probably about 26 feet to the first unit from the boiler outlet. 13 feet horizontal and 13 feet up.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,153
    Location:
    New England
    With the boiler off, open a bleed valve then open the fill valve. WIth the system open, you won't build pressure too high. You'll have enough pressure and flow to push water throughout the loop. Do this at each of the radiators that doesn't heat separately. Let it run for a minute or so unless you are still seeing bubbles (you'll want someone controlling the fill valve while you're opening the bleed valve). Shut the fill valve off before you close the bleed valve. My guess is you'll get the air out.

    Another thing you can try is put a hose on the drain valve...put the end in a bucket partly filled with water. Then, open the zone valve of where you have problems, and then open the fill valve. The flow of water under pressure should go around the loop and keep it up until you stop seeing bubbles in the bucket with the drain. With the hose in the bucket you have more flexibility since if it does try to suck any air in, since the end is in the bucket beneath the water, all it will get is water. Make sure you shut off the fill valve before you close the drain valve or you may get too high a pressure in the system.
    Last edited: Oct 22, 2009
  8. atelsth

    atelsth New Member

    Messages:
    16
    jadnashua,

    The fill valve is generally open all the time. Isn't that the way it's supposed to be?

    Should I try these things and then leave the fill valve closed when I'm done?
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,153
    Location:
    New England
    If the fill shutoff valve is always open, then there should be two devices after it: a backflow preventor and an autofill valve. The backflow valve is so the stagnent water in the boiler loop doesn't feed back into the house's potable water; and, the autofill valve is (or should be) set to the required system's fill pressure...in other words, if it is working properly, it should add water as necessary (this should not be very often as it is supposed to be a closed system...it should not have leaks!) and maintain the set pressure. The expansion tank accounts for the variations in volume of that closed system with changes in temperature.

    If the autofill valve is not working, then the system pressure could drop if you lost water from a leak. It also could allow the pressure to get too high if it leaked and allowed the street pressure to leak into the boiler loop.

    The autofill valves normally have an override lever on them that allow street pressure to get into the system. If you can isolate the boiler from this higher pressure with shutoff valves, you can use that higher pressure to purge the air out since that high pressure will flow through the pipes similar to what happens when you shut the house water off to do some work, then turn it back on...you'll get some spurts, bangs, etc. until all the air is purged out (this outlet is where you want a hose in a bucket for two reasons: one, you can see easier if you are getting air out from the bubbles, and two, if there is a momentary hiccup, it will suck water in rather than air). That is what I was trying to emulate. Do not do this if you can't isolate the boiler circuit, since things in there won't like the 40 or higher pounds of pressure you'd get from a straight connection to the street pressure.
  10. atelsth

    atelsth New Member

    Messages:
    16
    The fill valve is always on and I have a backflow preventor and a auto fill valve.My autofill valve does not appear to have an override on it and there is not a valve to isolate the boiler if it did.

    I guess that means the hose on the drain valve in a bucket of water won't work?


    Here are some pictures of the boiler and plumbing...

    http://s992.photobucket.com/albums/af48/cantstart/
  11. patsfan78

    patsfan78 Web Development | HVAC

    Messages:
    33
    Location:
    Maine
    If you isolate that zone, and add some extra pressure that will help to really absorb that air into the water and push it out. If that still doesn't do the trick we may have a flow/piping problem. But like others have said it really sounds like trapped air.

    Best of luck,

    Mike
  12. atelsth

    atelsth New Member

    Messages:
    16
    Problem Fixed

    All of my baseboards are now heating so I wanted to close the loop on this in case others are having a similar problem.

    For 2 of the three non working units, the air must have been trapped in the return pipe (the return pipe does a 180 after the bleed valve and travels back underneath the finned part and goes down through the floor a few inches from where the supply pipe comes up). By bleeding the baseboard with the supply valve closed, I was able to force the air out of the return pipe and get those two units working.

    The third unit, which was in the bathroom, was more stubborn. I would bleed it until I got hot water out of the bleed valve. This took about 6 cups of bleeding. Then I would close the supply valve and bleed the return pipe until I got hot water again, about another 4-6 cups. At this point, the pipes were hot from supply to return. After this, however, the baseboard would just cool down and not get hot again.

    I finally forced the trapped air out by making a higher capacity bleeder. I then turned the boiler off and pumped up the expansion tank to about 25 psi and bled the baseboard, After a couple of seconds of pretty strong flow, I got the air out and it has been working fine since.

    Below are some pictures of the high capacity bleeder before and during use.

    Thanks all for your help.

    [​IMG]

    [​IMG]

    [​IMG]
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