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L8184E, 2 circulators, one T calls, high limit exceeded

Have the Aquastst high limit set to 190F; when one of the thermostats (each thru a R845A) is calling, high limit does not work, it overshoots to 240F with lots of pounding, bubbling that starts at 220F before I chicken out to see if it will eventually kill the burner. When the other thermostat thru its own R845A calls, everything is fine. The one that has a problem is a very small baseboard loop run thru 1/2" copper. When both thermostats are calling both loops work, but sometimes when the small loop calls the circulator runs but does not circulate (air bound?)...supply and return lines are same temperature.

The install was done the old way, with circulators in the return lines, so subject to air issues. The main loop is actually an old radiator, gravity ladder. The new, troublesome loop is about 16' of baseboard in a 12 x 12 room. Replaced the automatic air valve and have bled system several times. The high limit control works fine, shuts the burner off at 190 or so when only the big, old system is calling. It's only when the small loop is calling by itself that there's a problem. The two R845A's are wired in parallel to the TV-T terminals, and the L8148E has damper control installed. The small loop circulator is a bit noisy but rather than replace it I;m wondering if a zone valve would be better, cheaper fix Other choice is to move circualtor to supply side. Final detail; reason I dug into this is to replace a couple radiators with baseboard in the main house.

Comments

  • STEVEusaPA
    STEVEusaPA Member Posts: 5,292
    Some opinions

    I think your high limit isnt working, or isnt working correctly, for starters.  It should either work everytime or it needs to be replaced.  I would pull it, make sure you have some well grease, then reinsert it.  If the doesnt fit snug in the well, make sure you slightly bend the wire to ensure the bulb is making contact with the well.  Then fire it back up, either on the small zone, or disconnect the circulator and let it run up the temp and see if it shuts off on high limit.  If it doesnt, or does sometimes and not others, you need to replace it.

    The small zone just might be the reason why it's running up to limit, but the limit should work when either zone calls, and shut down the burner.

    Checking the smaller zone circuit.  Go through your basic trouble shooting. Check all wire connections. Going into the relay, are you getting 120v?  Coming out of the relay, are you getting 120v (when the tsat is calling for heat)?  Check your low voltage side. Going into the circ, same testing.  If everything is ok there, then you can move on to see if the zone is getting heat.  Do you have enough pressure?  Did you confirm with a separate gauge?  Bleed the zone again (circ off).  Call for heat in the zone, check supply and return pipes.  Could be bad/wrong circ, bad impeller, flow check stuck, or built up with crud and cant fully open/close.  This might be why you get heat when the other zone calls.  Is there a flow check on this loop?

    You could repipe with one circ with a zone valves.  However, you might run into a balancing problem when both zones are calling.  So you will need to consider that with a re-pipe.

    I would solve your first problems via troubleshooting, and worry about re-piping and a different control strategy second.  Like resident gure Icesailor always says, If it was working before, what changed?
    steve
  • AZNHBob
    AZNHBob Member Posts: 17
    thanks

    I agree, tracing down an erratic, illogical problem means a systematic checkout, which I attempted. I did verify the wiring, looking for some sneak path, but I can think of no way for a good high-temp limit to fail every time only the small loop is calling, but be OK on the large zone. What I need to do next is actually observe the burner to see if the high temp limit has worked, maybe it's just the "thermal momentum" of a boiler way oversized for the small loop (163 BTU/HR) with an erratic pump that carries the temperature over the limit.



    As to what has changed, well, other than draining the system, and dead ending two radiator rungs, then refilling, the only other possible issue was the pump may have been dead-ended the first time the hammering commenced. No one is sure if the ball valve above the circulator was in the open or closed position when the system was refilled and started up. And I read that exceedng the punp temperature limits are easy to do in that situation. And the pump on the small zone is noisy. And fussy about whether or not it's working. There's no air bleed on the baseboards, but the new automatic air bleed seems to be working fine. And yes, there's a checkvalve on that zone, but no boiler bypass piping anywhere.



    I see that on 2 circulator systems the preferred connection is for one circulator to be on the L8184E, the other on the R845A, but again, just as you have said, high limit should work no matter what. I'll doi just as you've recommended, get some well grease and re-do the thermowell.

    Thanks again
  • icesailor
    icesailor Member Posts: 7,265
    Bombs in the cellar:

    Somehow, you have a wiring issue. The High Limit part of the control is being over ridden by the small zone. If the second zone is the "845" relay, it is wired so that when the circulator is running, the burner is supposed to do the same, but be interrupted by the High Limit side of the 8184E. If the zone with the over-ride on it doesn't stop, disconnect the black feed wire at the circulator while It is supposed to be running, and if the circulator stops but the burner doesn't stop, then, remove the wire on the "845" and see if the burner stops.If it does, then you have a cross wiring situation.

    If you properly used the ZC/ZR feature on the second zone, this won't happen. If it is wired wrong, it can cause this because the ZC/ZR over rides the "operating" part of the 8184. Somehow you have over ridden the High Limit. If you turn on the primary zone that seems to work properly, and you have it running, with the "Lo Limit" set for 120 degrees or lower, turn the High Limit down  to below the boiler temperature and the burner should stop, but the circulator should keep running. That's how it is supposed to work. If you turn on the the 845 zone and the boiler temperature is say 150 degrees, turning up the thermostat should make the circulator start AND the burner at the same time. If you turn the "High" limit down below 150 degrees, the burner should stop but the circulator should keep running until the thermostat is satisfied. If the above doesn't worked as described, it is mis-wired.

    So far as the circulator being on the returns, get that out of your head for now. Where I travel, 95% of all hydronic systems installed before 2000 have the circulators on the return. Where they now want the primary circulator on tea pot boilers to be. Pumping IN to the boiler and having cooler water going through them. If you first, re-pipe the boiler and you still have the same problem, you will be back to the wiring.

    What I used to see all the time was that the "845" second zone, not wired through the ZC/ZR and the zone ran independently of the boiler controls and only ran the circulator while the boiler ran on the operating control.

    It is highly unlikely that the 8184 is defective if it will properly run the main zone that is connected to it. The boiler isn't all that big. And if it was bigger, it wouldn't make all that much difference. It should still work.

    It's also why commercial installed boilers require a secondary high limit with a manual re-set.
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    edited May 2012
    Is this a two zone system

    or is it a three zone? If it is a two zone get rid of one of the 845's and use C1 and C2 on the L8148E for one zone thermostat wired to T and TV. Then wire the 845 terminals 5 and 6 on the other zone through the limit on the L8148E (B on the limit and B2 on the relay) and the circulator off either 3 or 4 (depending on location of the jumper on 845).



    By the way there is no ZR and ZC on the L8148E relay so that is not an option.
  • AZNHBob
    AZNHBob Member Posts: 17
    2/3 zone, limit switch

    Yes, its a 2 zone and clearly there is a wiring problem, plus maybe a check valve issue. Ran a series of tests. after I replaced the zone 2 circulating pump.

    1. Disconnect zone 2 thermostat, adjusted hi limit to 180 and see how zone 1 functions. Called for heat via thermostat, ran it until high limit exceeded, and it shut down at about 185+; now I immediately connected zone 2 thermostat (calling) and burner comes back on, and both zone `1 and 2 circulate.



    2. Now I disconnect zone 1 thermostat and zone 2 pump runs but circulation stops and burner stays on up to 220; I immediately rereconnect zone 1 thermostat and burner shuts off immediately, aAnd now both zones are circulating.



    So:

    A. when only zone 1 is calling, everything works fine.

    B. when only zone 2 is calling, the zone 2 circulator runs but does not circulate, and the hi-limit is disabled.

    C. when both zones are calling both zones flow correctly but the hi-limit does not work.



    I don't know how long the system has been wired this way, but have to assume that normal operation is for the small zone (a sun room run at a lower temperature anyway) never to call before the zone 1, and always to be satisfied before zone 1 because it is such a small room.



    I do know I don't like it at all, when the high limit is disabled any how, any time.



    So Tim, is there an issue with the B on the limit when there is a vent damper? There is a wire on each B and R on this system.

    Thanks, All
  • Paul48
    Paul48 Member Posts: 4,470
    There

    isn't any external connection for B and R on the l8148e. There is a connection for B and R on an optional low limit control. There is so many unknowns about what you actually have, and how it's wired,it's hard to tell what could be wrong.Can you give a little more detail about the control setup. How is the damper wired?Is everything wired off a single power source?
  • AZNHBob
    AZNHBob Member Posts: 17
    details

    I appreciate everyone's input, and agree that a complete schematic is necessary. I have done one, but want to go back and double check before I post. The rest of the project that got me into looking at the boiler controls is at a critical stage, and right now we're well out of needing heat so it'll be a couple days before I get back to it. Right now I've got zone 2 disabled and will leave it that way until the hi limit problem is resolved, as it's only a problem when zone 2 is connected.

    Regards,

    Bob
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    Paul the L8148E

    has torx head screws on the terminals R & B the one is a no tamp (little tit in the middle) the other is not a no tamp so you can loosen it and wire to it. That procedure which I initially offered as a solution is not the best. Read on as to best way to solve this. I have e-mailed the poster a diagram showing how to do this.



    The vent damper is connected to a plug built into the L8148E and is powered by the call for heat initiated at T and TV on the relay. This will cause the damper to open and the end switches on the damper to close putting 24 volts back through the L8148E high limit circuit and then to B1nd B2 which will power the gas valve.



    The simplest way to wire this would be to have the R845's control the circulators for each zone. Then wire 5 & 6 off the R845's to T and TV on the L8148E. This will insure hi-limit protection and also operate the vent damper correctly. You would not use C1 and C2 on the L8148E.
  • Paul48
    Paul48 Member Posts: 4,470
    The

    schematics are very simple. I would just want to make sure there has been no cobbling done, and if optional equipment has been added, proper jumpers have been removed,etc. Probably over cautious, but I've run into a lot of things that seem straight-forward until you actually see them. Then it's like....What in the world is that!?
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    Not sure what

    "cobbling" is?  Actually jumpers need to be in place on the R845's from terminal 1 (120 Volt Hot) to terminal 3 or 4.
  • Paul48
    Paul48 Member Posts: 4,470
    The

    work of a cobbler,or shoe-maker.
  • AZNHBob
    AZNHBob Member Posts: 17
    I gots connections to B and R,

    OK the schematic and my wiring agree except that even with damper control I have connections (B has blue wire, R has green) both wires go thru a hole in the board. A retired contractor, here do do a different job looked at the system and marveled at how totally oversized most of the old piping was (from gravity days) and how poorly installed the old was, with lots of 90 el's instead of dual 45's, running probably 40 feet of 2" iron before the first radiator, lots of unnecessary fittings, etc. He said the system probably is heating 10 times the water necessary because of the huge pipes. Could that have anything to do with the inability of that loop to circulate unless the main circulator is running?

    And, what do the blue and green wires do inside the aquastat?
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    The B and R terminals

    are the high limit switch in the relay. Wire the unit as the diagram I sent and you will have high limit protection.
  • AZNHBob
    AZNHBob Member Posts: 17
    B, R, & 8148E High Limit

    Well, I have some other problem, then. The wiring agrees exactly with the schematic I found earlier for a 2 circulator circuit, and your 3 circulator one. The only chance for an error that I could see was if B and/or R somehow should not have connections because of the vent damper. So my original problem remains, which is that only when zone 2 is calling, the high temp switch fails to function. When zone 1, OR ZONE 1 AND ZONE 2 CALL, the high temp switch works fine. Very weird, very worrisome.
  • AZNHBob
    AZNHBob Member Posts: 17
    Ah-hah moment?

    Thinking about how the system was working, it occured to me that since the 1 1/4 supply and return lines of the main zone, with the big B&G circulator were as close to the 1/2 inch porch zone as the boiler, maybe the porch zone wasn't even seeing the boiler when it was the only zone calling, and with no circulation, the boiler overheated faster than the aquastat could respond. I mentioned this to an HVAC guy, and he said maybe the main loop check valve isn't working. I said there is no check valve. There's only one, and it's in the porch loop. He said every zone has to have a check valve. Seems to make sense, so Is that correct?



    Further, I'm thinking that I should put in a small 3/4 restriction so the main loop and my new baseboard loop are better matched. Is that sensible? I plan to put in a 3/4 check valve in both the main zone and my new baseboard zone, so I will have 3 total.



    I figure I will also have all 3 zones run off the same thermostat just to be safe, with this huge Burnham boiler and just a couple baseboards, it seems to me they are just too small a loop for the high temp control to respond before the temperature runs up.



    Comments? Advise?

    Thanks all

    R Howe
  • Zman
    Zman Member Posts: 6,957
    Pumping Away

    I am not convinced you have a control issue. I guess you could have a bad (or miswired) operating stat and high limit stat. It just seems unlikely. Have you checked you temp gauge to be sure it is giving reliable info?



    Back to the problem. The noise you describe sounds a lot like air (steam actually). If you have several larger circulators all working to draw the pressure down on there inlet side, you could actually be creating negative  pressure in your system. Your water could be boiling at or below 190. Your temp gauge may be reading 240 (the temp of the steam) and the high limit 190 the temp of the water.



    Where is your expansion tank located in relation to the circs?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Paul48
    Paul48 Member Posts: 4,470
    Information?

    Please post the wiring diagram you drew up, and make a simple drawing of the piping of your system,and post that also. At this rate, the problem will never be fixed. No offense, but you're giving us information in dribs and brabs, that you think  is pertinent, and then asking what we think.If we know exactly what you have, we can tell you what is wrong or how to troubleshoot it. No guessing involved.
  • AZNHBob
    AZNHBob Member Posts: 17
    info

    With all due respect, if I had posted every detail, I would have gotten flamed for I'll bet. My initial post indicated it was an old gravity ladder system converted to a circulation pump in the return leg. That suggests large diameter piping, I'd say. Note the 2" lines in the return.

    The piping diagram is an excellent suggestion, and it is attached, along with the wiring diagram I was sent, which matches what I have (for 2 zones), and a photo. I have a more detailed piping diagram, where I identifiy every fitting. And that caused me to look carefully at one old T that turned out to be, yes, a check valve on the main system. Missed that until I did the diagram. So now I am truly stumped.

    I started this out by just wanting to replace a radiator with a baseboard. I did that, with 3/4 copper and a I get essentially no flow in the baseboard. I throw in a circulator I still get no heat. If the main loop checkvalve is working, how can that be if the pump is running in the right direction? I suppose I can toss in a checkvalve, but there is already a rung using 1/2 copper that works fine with no checkvalve and no circulator.
  • AZNHBob
    AZNHBob Member Posts: 17
    diagrams, photo

    somehow didn't come thru. 2 more to come after convert format.
  • AZNHBob
    AZNHBob Member Posts: 17
    diagrams, photo

    somehow didn't come thru. 2 more to come after convert format.
  • AZNHBob
    AZNHBob Member Posts: 17
    photo

    wiring to come, but it's standard 8148E with 2 845's but forum won't accept .doc format
  • AZNHBob
    AZNHBob Member Posts: 17
    expansion tank

    see photo posted: it's just behind the boiler, and top is hot, bottom not.
  • Paul48
    Paul48 Member Posts: 4,470
    Try

    hooking that circulator up to the return line of the zone, not the supply of the boiler.Lose the 1/2" on the inlet side of the circulator. It's like pumping a pool out through a straw. The pump is cavitating.
  • Zman
    Zman Member Posts: 6,957
    Expansion Tank

    Where is the air eliminator and expansion tank in the piping diagram?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • AZNHBob
    AZNHBob Member Posts: 17
    return line

    actually that's where it is, and that's what I thought I showed in the diagram with the directional arrows.
  • AZNHBob
    AZNHBob Member Posts: 17
    air eliminator

    both are in the supply line, after the pressure regulator. The expansion tank is just behind the Burnham, about 6" below the air eliminator.
  • AZNHBob
    AZNHBob Member Posts: 17
    lifeline: 50:50

    I think I'm going to eliminate a couple wrong answers: boiler control and separate thermostats for the two small zones. Instead of wiring the thermostats in paralles woth the 8148E thru the 845's, I'll just let the zone 2 thermostat control the circulator, not the boiler. That way when the main house is calling, the porch gets heat. When not calling, water will circulate which will prevent freezing in the occasional below 32 days here, but will not cause the boiler to fire, because that's when the aquastat slow response time causes the overheat before the high limit kicks out. There is no circuit interaction between the zone 2 845 and the high limit, concern that there was led to my original confusion. With such a huge boiler and a skimpy 16' baseboard on 1/2 copper, it overshoots in about a minute, maybe 2. Running the main zone balls to the wall, it takes over an hour and a half to get the boiler up to 190F because of the oversized piping. I'll just hook my new baseboards to a separate loop, with its own TACO circulator and FloChk 218, to be powered up only when the main zone is calling and circulating.

    Thanks all, and for this forum.

    Bob Howe
  • Paul48
    Paul48 Member Posts: 4,470
    Sorry

    I was confused by the fact that you called out the dimensions of the tee connecting it to the supply of the boiler, and that would just form a boiler loop.
  • Zman
    Zman Member Posts: 6,957
    not ideal

    Ok,

    Pumping into the tank is not ideal and is certainly not helping the air removal. Since both zones have equal access to it I doubt it is the source of the problem.



    I like the theory of the lack of check valve in the big loop. If this theory is true, you would have water from the small circulator flowing backwards through the big zone, and not through the boiler (causing a rapid temp spike) This is very likely in a converted gravity system, because the pipes are huge.If you had an isolation valve on the big loop you could close the valve and see if the problem goes away.With no valves you may figure it out  by observing the pipe temps.



    Did this problem start with the addition of baseboard? How was it piped?



    Does the boiler come up to temp and cycle normally when the big loop is calling or does it never reach it's operating temp.



    Please let us know how this turns out.

    This is an interesting one.

    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • AZNHBob
    AZNHBob Member Posts: 17
    failure to communicate

    sorry, must have misused the terminology: the water supply line to feed the boiler is where the expansion tank is; I don't know how that's piped in to the boiler , whether it's a separate port or is directly connected to either supply or return lines.

    A prior post corrected my notion that the main loop had no checkvalve. It has one, I just didn't recognize it as such. There's a lot in this system I didn't recognize at the outset, and I still don't know if there's a rationally for all the different pipe sizing and multiplicity of fittings.



    Actuallly there are several valves in the gravity system, but all are downstream and all are open.



    Problem started when I tried running the zone 2 small baseboard via 1/2" copper by itself to see if that's how I should add the new baseboards. The boiler took off, hit 240 clanking and bubbling in under a couple minutes, and showed no temperature difference between supply and return of zone 2. Soon as I enabled zone 1 circulator, the temp dropped to 140. Zone 1 alone always runs fine, hi limit works, cycles, and behaves like it should.



    Several new baseboards are about to be added.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Several new baseboards are about to be added.

    If hot water does not flow through them, it will not help no matter how much baseboard is added.
  • AZNHBob
    AZNHBob Member Posts: 17
    baseboards added

    I realize this is a long thread, but if you go back and follow the developments you'll see that the lack of flow by just replacing main zone, gravity-converted-to-circulator (ie laddered runs, large diameter pipes ranging to 2") radiators with 3/4" copper baseboards is what started the issue. It didn't flow, so I looked at the second zone, 16' of baseboard fed thru 1/2" copper which had its own thermostat, circulator, and checkvalve, all wired in parallel with the main zone. When I ran the second zone by itself, it very quickly overheated and failed to circulate. The Hi-Limit switch did not shut off the boiler at 190 which led to thinking a wiring error was disabling the switch. Instead, it looks like the 8148E aquastat design is for fairly slow response but the tiny loop, starved by 1/2' feed but heated by a 163BTU boiler was like a nitro-fueled funny car engine in a Yugo. So I decided I would not copy that design for my new baseboards. And I decided to remove boiler control from zone 2 thermostat/845 solenoid.

    I'm adding a separate loop for the new baseboards (zone 3) with its own circulator and checkvalve, no thermostat, and wired to circulate whenever the main zone circulator runs. Zone 2 will circulate whenever its thermostat calls, which will supply that zone with heated water whenever zone 1 is running, and with tempered water whenever zone 1 is not running, which will keep it from freezing in the winter without adding appreciably to the heating cost.

    That's it in a nushell.
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