No Heat on Most of Top Floor Zone

Discussion in 'HVAC Heating & Cooling' 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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    You need to add more water to raise the pressure. the expansion tank (with no water pressure on it assuming it is a bladder tank) should be set to the normal working pressure of the system, so in your case 30#. Sounds like you still have some air in the system, but raising the operating pressure may help purge some of it. If the water circulates, the air will migrate to the top, but if there are any dips, and it doesn't circulate, it could be caught elsewhere, and adding water to up the pressure should help the circulator get water to those upper floors.
  3. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,143
    Location:
    South*East
    If your getting water out of the vents on the 2nd floor you have enough pressure on the boiler. If it's a two story house then 12# to 15# is the pressure it should be. The relief valve would open at 30#. You may not be opening the vents long enough. You should draw about a 1/2 cup of water out of the vent You also say the valves are working hard. Check to be sure the stem is turning with the handle. I have seen the handles strip with time. You will still get water out of the vents with the valves off. It will come in from the return side. What type of baseboard do you have. ( copper fin or cast iron)

    John
  4. atelsth

    atelsth New Member

    Messages:
    16
    Thanks for the replies.

    It's a 3 story house, including the basement which also has baseboards. The baseboards are copper pipe with aluminum fins. The copper pipe comes up through the floor, feeds into the baseboard, and then comes back, under the fins so that it goes back down through the floor just a few inches from the feed pipe.

    One of the valves is not turning at all, the other 3 work fine.

    I will try bleeding it some more. As of this morning, the problem seems to be affecting the 2nd floor baseboards also. The thermostat was calling for heat, the boiler was heating water and it was circulating around the main run of 1.25" pipe, but there was no hot water getting to the 2nd floor baseboards which are less than a foot above the runs of 1.25" pipe.

    I think the nameplate said the operating pressure was 30# for water but I'll double check it and the paperwork.

    If the pressure to expel the water from the bleed valve is coming from the return side and if the radiator is slightly tilted so that the bleed valve is downhill, is it even possible to get the air out by bleeding? I don't think this is my situation but I'm curious.

    I was able to prop up one side of one of the 8 or 9 foot baseboards so that the bleed valve was well above the on-off valve and the point where the feed and return lines go horizontal and only water came out - no air.

    I'll try the suggestions I've gotten and post back.

    Thanks.
  5. atelsth

    atelsth New Member

    Messages:
    16
    I took about 3 cups of water out of each of the 3 baseboards that were not working but did not get any air. I then tried elevating the end with the bleed valve, opposite the fill valve, and I did get some air out.

    After another 2 cups or so, hot water came out. However, it only flowed as long as the bleed valve was open. After I closed the bleeder, it cooled down and that was that.

    Could this be because the pressure in the boiler is too low? It reads 20 to 22 pounds when the circulator is running. The plate says the maximum operating pressure for water is 30#.

    What should it be pressurized t in a 3-story house?

    Could it be a weak circulator?

    Thanks.
  6. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,143
    Location:
    South*East
    If your getting water on the top floor there is enough pressure in the system. If the circulator is moving the water in the main it's OK. How many zones are on the system? Do they each have there a circulator or are there zone valves? Could it be that the top floor is on a loop system not coming of the main? It would be a big help if you could post a picture of you boiler & piping. There may be a way to purge the system to remove the air.

    John
  7. atelsth

    atelsth New Member

    Messages:
    16
    Thanks for the reply johnjh2o1.

    It is definitely a one pipe system for the top floor. There are 3 zones: basement, 2nd floor, & 3rd floor. There is only one circulator which was originally a 1/12 hp B&G. It uses Taco zone valves.

    I just put a pressure gauge on the expansion tank and it reads 14 psi.

    I will try to get some pictures of the piping but basically from the boiler output, the pipe splits into three branches, each with a zone valve. After the zone valves, the three main pipes run around the bottom floor at cieling level and combine back into a single pipe before running down to the circulator pump and back into the boiler. It has a Fill-Trol bladder type expansion tank and an auto fill valve and an American air purger.

    Thanks
  8. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,143
    Location:
    South*East
    Check the Taco zone valves they may not be opening. There should be a way to open them manually.

    John
  9. atelsth

    atelsth New Member

    Messages:
    16
    I'll check the zone valve but I don't think that's the problem since:

    1. When the 3rd floor is calling for heat, the pipe on both sides of the zone valve quickly heats up.
    2. The main pipe for the 3rd floor also heats up all the way around the its basement run back around to the circulator.
    3. One of the baseboard units on the third floor zone heats up and works as expected. It is the 3rd set of 4 T's off of that pipe.

    I'll check the zone valve and post back tomorrow.

    Thanks
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    That 30# is likely the max before the safety dump valve (pressure relief) opens.

    The air pressure in an expansion tank is the same pressure as you have in the overall system. Assuming it is a bladder tank, the only way to check, and adjust if necessary, is to open the water system to relieve the pressure on the wet side of the bladder and then measure the air pressure in the tank. think of the bladder as a balloon in a bottle. If you put pressure on it, the balloon will compress, raising the internal pressure, remove the pressure (in this case water on the other side), and the balloon expands and sits at its static pressure. Your system probably runs around 12-15#...it should not jump to 22, the expansion tank should allow that expanding water to move in there and the water pressure will stay fairly constant.

    If your air pressure gauge isn't very accurate, you might get different readings from the boiler's pressure gauge and your tire pressure gauge, but otherwise, when the system is operating, they will be the same, and if accurate, the gauges should be identical.

    It doesn't take all that big of an air bubble to block the flow.
  11. atelsth

    atelsth New Member

    Messages:
    16
    Thanks jadnashua.

    So to correctly check the pressure I need to do it with the system drained?

    Actually the two pressure readings may not be that different. Because it was not easy to get to, I never did get a tight seal between the valve and the tire gauge when I measured. Also, I measured with the system cold and at that time the pressure/temp gauge on the boiler was reading about 18#. I will check what my relief valve is set at but the name plate says it should be a max of 130 psi.

    The only thing that makes sense for this problem is a blockage, and since it's 3 out of 4 baseboards in one zone, it is probably air. But in 2 days of bleeding, I've probably taken 6 cups of water from each baseboard. Could there be a not quite horizontal run of pipe somewhere that is trapping the air and not letting it go? There would have to be one in each radiator branch that is not working.

    If so, would raising the pressure a little help "knock" the bubbles loose?
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    To check the expansion tank pressure, you don't need to drain the system, just open the drain valve enough to get the water pressure to zero (make sure the makeup water valve is closed and the boiler is off). If in the loop you have a fill valve and can make all of the water go all the way around the loop before it gets to a drain, you could open the fill valve and the drain valve and let it run. You don't want to constantly replace the water in a closed boiler system since new water carries oxygen and other possible contaminants in it - oxygen causes rust. Ideally, the thing gets filled once and the purge systems that remove air get it all out, and you go on from there.
  13. atelsth

    atelsth New Member

    Messages:
    16
    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]
  14. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    Geez & I was going to say start a 3rd thread
    Cause 3's the charm ;)
  15. NYCSuperintendent

    NYCSuperintendent Superintendent

    Messages:
    1
    Location:
    NYC, Queens
    High capacity bleeding

    I'm a superintendent (head of maintenance) in NYC for a 368 unit that uses a Hydronic System for heating and one of my problems is to bleed this convectors. I came with and idea similar to what you are using but instead of a ball valve I'm using a small 1/4" shut off valve in which I can attach a hose to bleed the convector/radiator. Here is a picture of before and after.
    Before

    [​IMG]

    After

    [​IMG]
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