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Zone that doesn't heat properly

ntonkinntonkin Posts: 126Member
edited January 29 in Gas Heating
I replaced a Weil Mclain HE4 propane boiler with a Lochinvar Knight KBN106 about 5.5 years ago. I have 6 zones now but had 4 zones before I replaced the HE4.

Zone 1 = 466 sq. ft. with 16' of baseboard slant-fin radiators and 3/4" copper pipe under the slab.
Zone 2 = 475 sq. ft. with 20' of baseboard radiators
Zone 3 = 367 Sq. ft. with 17' of baseboard radiators
Zone 4 = 407 sq. ft. with 15' of baseboard radiators
Zone 5 = 840 Sq. ft. with pex in concrete garage floor
Zone 6 = 547 sq. ft. + stairwell with 38' of baseboard radiators

The smallest zone (3) will not maintain above 65 degrees and the thermostat thermometer never reads above 58 degrees even though an accurate thermometer in the middle of the rooms reads 65. The zone is almost always calling for heat. This is the case whenever the outside temp is below freezing. No other zone has any trouble heating the space up to where the thermostat is set. Zone 3 is also the closest zone to the boiler. The zone worked fine before replacing the HE4.
Before I called for help I had cleaned radiator fins, flushed the zone, replaced the thermostat, replaced the pump for the zone and switched positions on the controller.... all with no change. After the Tech support guy at Lochinvar suggested monitoring the delta T for the zone (which was negative as it turned out) I installed a backflow preventer in the return line - - still no change. The next tech suggested I change the position of the expansion tank connection - still no change. He also suggested flushing out the anti-freeze and cleaning the system, refilling with only conditioned water. Left the cleaner in for 2 weeks then refilled with water and conditioner. Still no change. As I see it there is nothing left but to tear out the piping and replace with new clean pipes. when flushing the zone there seems to be no restriction in flow through but there must be something restricting flow that limits the amount of heat the radiators emit. I have had 4 different heating Techs come to fix this problem and none of them could figure out how to correct this issue... everything done so far really hasn't even improved the situation noticeably.

Has anyone run across a problem like this - - any suggestions?


    Do heating elements get hot? Have you tried turning off other zones and running only zone # 3
  • ntonkinntonkin Posts: 126Member
    Yes & no, they put out a modest amount of heat but not like the radiators in other zones. and yes, I have shut off all the other zones - - still the same.
  • Intplm.Intplm. Posts: 684Member
    I have run across this problem before.
    As to the new installation. Were the pipes soldered, pro-press or pex installed?
  • unclejohnunclejohn Posts: 1,362Member
    Delta T means a change in temp and would be a drop in heating. Are you saying the water temp stayed the same in and out of that loop? What do you mean by negative?
  • ntonkinntonkin Posts: 126Member
    edited January 29
    Pipes were soldered. The only pex is in the garage floor zone. What I mean by "negative Delta T" is that the return temp was higher than the supply temp. I know that it makes no sense but I checked it numerous times and that was what it was. I have no idea how that could happen. I switched the thermometers and same result.
  • Intplm.Intplm. Posts: 684Member
    I'm leaning toward an obstruction. But a partial or intermittent obstruction. I sure would like to know or see how it is piped .
    This kinda thing can make you crazy.
    @ntonkin solder? propress? or pex tubing?
  • ntonkinntonkin Posts: 126Member
    Pictures of my system:

  • Intplm.Intplm. Posts: 684Member
    I found a lot of solder caught in areas near valves or circulators. The problem is that it gets caught in these certain spots and when the circ. stops it falls back into the pipe no longer causing the restriction. The area that the solder gets caught in acts like a next so enough water can flow visibly but not enough to provide heat.
    Since you have been so thorough so far. Do you think that you might have this type of obstruction.
    It's happened to me.🤯
  • Intplm.Intplm. Posts: 684Member
    Acts like a net not next as written above.
  • ntonkinntonkin Posts: 126Member
    edited January 29
    Hello Intplm,
    Thanks, you must be right... the only thing is that I've not done anything to that zone except remove a zone valve and install a pump in it's place - I can't imagine how solder would get in there. This zone heated just fine for 22 years. I've replaced the pump once so the obstruction can't be in the pump. How do you deal with clearing this kind of obstruction - short of replacing the copper pipe in the zone? I do have air bleed valve elbows on each of the three radiators in the zone.
  • neilcneilc Posts: 659Member
    how can the return be hotter than the supply ?
    is the circ pumping the wrong direction ?
  • ntonkinntonkin Posts: 126Member
    edited January 30
    That's a very good question and I have no idea. It doesn't make any sense and it's hard to believe isn't it? I switched the contact thermometers around and adjusted their position and nothing would change the resulting readings which were crazy. As you can see in the picture, all the pumps are in the same direction. That's why I put the back flow preventer just before the zone joins with the other returns so the zone can't flow backwards. You can see it in the 921 photo at the very top of the picture if you enlarge it (light is shining right on the preventer).
  • neilcneilc Posts: 659Member
    not sure I see that check,
    but raises another question,
    are the other zones checked ?
    could this zone be drawing cooled water from other zones not circing?
    try closing all other zones by ball valve, and thermostat turned down, and see if temp makes sense on troubled zone.
    ah, that makes no sense either, the return is still hotter, still.
    It's gotta be flowing backwards.
  • neilcneilc Posts: 659Member
    you sure green pump isn't pumping down
  • DZoroDZoro Posts: 752Member
    Do all the pumps have checks in them? Does the radiant floor pump have a check? Hard to tell from the pic but there is a good chance the trouble is the radiant floor mix valve and pump. Valve off the radiant flooring zone entirely, supply and return, and then turn on the trouble zone and see if that makes a difference.
  • SuperJSuperJ Posts: 478Member
    edited January 30
    You have to look at the pump impeller housing to tell the direction. It’s possible the casting is upside down but the motor rotated to match the others.

    I think your header piping might be a bit undersized, which may cause undesirable interactions between the zones.

    Is the temp delta still backwards if it’s the only zone pump running?

    Are you sure the pump is getting proper power, maybe temporarily feed it power from an adjacent zone pump as a check.
  • GordyGordy Posts: 9,264Member
    edited January 30
    If it worked fine for 22 years you have to ask what’s changed?

    You replaced the pump. My money is it’s backwards, or air locked.
  • ntonkinntonkin Posts: 126Member
    All the pumps have check valves in them. I have tried shutting off all the other zones and it doesn't help. The delta T is now 25 degrees as it can't back flow now. I'll check the garage floor zone tomorrow morning.
  • SuperJSuperJ Posts: 478Member
    What about the zone with the mixing valve, does it have a check on the supply (not just the pump since the pump is inside the mixed loop)? Theoretically you could back flow through the thermostatic valve. Some thermostatic valves have built in checks. If there are checks everywhere maybe one of the checks has failed or cruded up? It sure seems like a back flow problem.

    Can you somehow prove if you have flow even if the temperature isn't what you want? If you do then it's flowing backwards from an adjacent zone to feed the trouble zone. If you don't have flow than it's some sort obstruction, air, or a pump problem.

    To prove this isn't happening valve off the supply (don't just shut the pump off).
  • ntonkinntonkin Posts: 126Member
    The delta T for the zone is +15 degrees (ie; supply side is 15 degrees hotter than return side this morning and there is heat coming from the radiators therefore there must be some flow in the right direction but it is still calling for heat continuously and never gets up to the set temperature.

    There is no check valve in the garage Zone other than in the pump, unless there is one in the mixing valve. I'll try shutting off the garage zone this afternoon when I return.
  • ntonkinntonkin Posts: 126Member
    edited January 30
    neilc & SuperJ,
    I double checked all the pumps and the arrows on the pump body are all pointing in the right direction. I put a back-flow preventer
    to prevent getting the hotter return and haven't had that issue since. all the grundfos pumps have a sticker that says "with check valve" and the green TACO has a sticker that says "integral flow check"
    It is very rare to have more than 4 of the 6 zones calling at the same time and I don't think I've ever seen all six calling at once. The pump that was taken out of zone three is now in the garage flow zone.

    first change was replacing a zone valve with a pump, then I replaced the pump with an identical pump. Those are the only changes I've made since I put the zone in service in 1991. The very first thing I did when I started having this problem was to crack the vent valves on each radiator. Then I flushed the zone several times and it seemed to flush through freely each time.

    There is no check valve on the supply line to the garage zone. I just had the garage zone shut off (both supply and return) for an hour and a half with no change in heating in zone 3.
  • ntonkinntonkin Posts: 126Member
    edited January 31
    The manifold in the garage zone is labeled "Viega" and I looked through their current product line and didn't see anything that looks like the manifold I have. However all of their current manifolds have no check valves within them.

    Zone 3 (the problem zone) now has a back-flow preventer on the return (just before it merges with the other zone return lines) so I don't think it's possible for it to flow backwards anymore. The Delta T on this zone varies between 15 and 25 degrees and I think this variation is due to how the boiler is firing at that particular time.

    The only way I think I can prove there is "flow" is that the radiators are giving off heat. Is there any other way to verify that there is in fact flow through the zone?
  • ntonkinntonkin Posts: 126Member
    OK, I just shut down all zones except for 3 for over 20 minutes. No increase in radiator heat flow and no increase in temperature in the zone. I did notice that when I went down to turn the other zones back on, the supply temperature to the manifold had dropped to just about the same temperature as the return temp of zone 3. Why would it do that?
  • SuperJSuperJ Posts: 478Member
    When you say shut down the other zones. Did you actually close off the ball valves to the zones or just turn off the pumps.
  • SuperJSuperJ Posts: 478Member
    The check valve for the garage zone should be between the header that feeds all the zones and the mixing valve. The check in the pump or manifold won’t necessarily do much since it’s behind the mixing valves.
  • BrewbeerBrewbeer Posts: 575Member
    Zone 3 could have higher average heat loss than the other zones. Longer radiators or higher output radiators might help, but you said you have a temp delta of 15 degrees through 17' of baseboard? Is this correct?
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread:
    System Photo:
  • ntonkinntonkin Posts: 126Member
    edited January 31
    Yes all ball valves closed except zone 3. Ok, I'll have to get that check valve in after it warms up.
  • ntonkinntonkin Posts: 126Member
    This just seems crazy, after shutting off all the other zones for 20 minutes, the Delta T on zone 3 is barely 5 degrees. Before, it was 15 - 25 degrees. The heat given off by the radiators doesn't change significantly at all. This just doesn't make sense. The boiler seems to be working normally and the other zones heat fine. It's -16 outside now so if most zones were not working, I would know it pretty soon.
  • ntonkinntonkin Posts: 126Member
    This morning it is -32 outside and the temperature in zone 3 has dropped to 62 degrees in the middle of the zone and 55 on the thermostat (which is set at 65). All the other zones are holding the set temperature. The Delta T for the zone 3 is 7 degrees. The boiler is running steadily at 100% with a Delta T of 24 degrees and now all six zones are calling for heat. The latest recommendation from the local tech is that I add a buffer tank to the system. Does anyone think that would cure this problem?
  • JellisJellis Posts: 110Member
    edited January 31
    Hello @ntonkin in reading your post i wanted to clarify a few things that are concerning to me.

    "first change was replacing a zone valve with a pump, then I replaced the pump with an identical pump. Those are the only changes I've made since I put the zone in service in 1991. The very first thing I did when I started having this problem was to crack the vent valves on each radiator. Then I flushed the zone several times and it seemed to flush through freely each time."

    "Zone 3 (the problem zone) now has a back-flow preventer on the return (just before it merges with the other zone return lines) so I don't think it's possible for it to flow backwards anymore. The Delta T on this zone varies between 15 and 25 degrees and I think this variation is due to how the boiler is firing at that particular time. "

    Based on what you stated here you now have 2 checks in the loop, one in the pump and one that you installed. I responded to many calls for similar issues to this, very low or no flow through baseboards on a call for heat.
    Multiple times one of our new techs had replaced a circ pump with a new circ that included an internal check. The circ would then have to overcome to check's in the line and this would greatly reduce flow.
    The plastic checks can be removed from the pump quite easily, just break it out. This may be your problem.

    That would explain why you are able to purge water through the loop just fine, the water pressure would be enough to overcome the checks.
  • ntonkinntonkin Posts: 126Member
    Hello jellis,
    Thanks, I will give this a try. Can the check be reinstalled if removing it has no effect?
  • JellisJellis Posts: 110Member
    you have to break it out of the pump so no, once you remove it you cannot replace it unfortunately.
  • ntonkinntonkin Posts: 126Member
    I tried changing the pump speed on zone 3 from low to medium but that seemed to only reduce the Delta T from 7 to 2 degrees. So I changed it back to low and the delta went back up to 7. Outside temp is up to -12 now and temp in the Zone is up to 64. I'm not going to take the check valve out until it gets warmer out.
  • GordyGordy Posts: 9,264Member
    edited January 31
    I see a lot of delta t measurements, and room temp measurements, but what is the actual temperature going into the zone, and coming out of the zone base board?

    Delta t measurements can mean many things. Wide, or narrow.

    In the end if the room is not meeting setpoint, and it use to assuming at the outdoor temps you are experiencing now not meeting set point. Something is wrong.

    So what is the temp into, and out of the baseboard. At the baseboard?

    If your boiler is running 100% a buffer tank isn’t going to help your problem zone.

    You also indicated that before replacing the boiler you had 4 zones, and now you have six zones.

    Was zone 3 the problem zone one of the new zones?
  • ntonkinntonkin Posts: 126Member
    No, zone 3 was one of the original zones in the system and always worked fine until I put in the new boiler and the two additional zones. I have been measuring the zone delta T with contact thermometers - one right below the pump and the other one is on the return line 18" before it joins the other return lines heading back to the hydro separator.

    The outside temp is up to -8 and the delta T has dropped to 3 degrees.

    I'll move the thermometers up next to the radiators and see what that shows.
  • ntonkinntonkin Posts: 126Member
    Temperatures at the radiators are: 145 in and 115 out. I guess the only way the return (where I previously recorded) could be so high must be heat transfered from the returns on the other zones.
  • GordyGordy Posts: 9,264Member
    Why are you only getting 145 to your baseboard?

    In those temps I’d be looking for 170 awt.
  • GordyGordy Posts: 9,264Member
    What is the boiler putting out? Supply water temp?

    Is the outdoor reset hooked up?

    IS the heating curve programmed correctly if it is?
  • JellisJellis Posts: 110Member
    @ntonkin do you get similar temps at other baseboard in the house? you could be getting low temps at this baseboard due to the restricted flow we were talking about earlier.

    i experienced similar issues at the service calls i referenced, warm baseboards but never hot.
  • GordyGordy Posts: 9,264Member
    I see you have a hydraulic separator.

    It would be helpful to also know the supply, and return temps going into, and out of the boiler side of the separator, and the supply, and return temps going out of the separator.

    In knowing this we can start nailing down what the boiler is producing, and what the total system is using.

    The boiler side of the separator will see a constant flow.

    Being you are zoned with pumps the system side of the separator will see varying flows depending on how many zones are calling. If one zone verses all zones are calling for heat those flow rates will be very different going through the hydraulic separator. This will also cause different mixing temps with in the separator.
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