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L8148E aquastat/thermostat dilemma

lmanc2222lmanc2222 Member Posts: 12
I have a thermostat that shuts the heat off when set at 68* and turns it back on when it's set for 72*. The temperature of the room is 72*. What the heck? Apparently something is wired backwards but what? What am I missing here? I played with the anticipator going the full range and it remains the same for every setting. Is the thermostat hung upside down (mercury switch going backwards)?

Please help, boy it seems like I should know this but I just don't know.


  • neilcneilc Member Posts: 812
    What you describe sounds like a correct operation.
    The room is 72, you set the heat lower, 68, and it shuts off, set it back up to 72 and it is on again, makes sense from where I'm sitting.
    while that 4* spread seems a bit wide,
    maybe it's closer to 3?, or 2*?
    are you comfortable?
    want it hotter? try 74.
    want it cooler use 68, 70,
    Mine stays at 64.
  • lmanc2222lmanc2222 Member Posts: 12
    edited December 2018
    Something additional that I forgot to mention. The burner and circulator only run simultaneously. I can't seem to get the burner to run while the circulator is off to make water temperature. Hmmmm...I have to set the temperature wheel to 210* to get the gauge to read 190*. My thermometer reads 180*. Am I looking at a new aqua stat? Thermostat? Both?

    Geez. This elderly customer has been doing with marginal heat for quite some time.
  • neilcneilc Member Posts: 812
    yeah, that's a different reply, and might be beyond my wheelhouse,
    post a picture of that aquastat showing the setting(s) inside,
    there is likely an offset inside also, see if you can determine that,
    Unless you're well north of Ct, you shouldn't need 210, 190, or even the 180,
    sounds like a wrong setting, or possible miswired,
  • neilcneilc Member Posts: 812
    and rereading your 2nd post,
    again, it sounds like the thermostat is satisfied,
    why bother trying to hit high limit after that?
    just wasting that fuel,
    you might just have a correctly, or closely sized boiler,
    what boiler temp are you at when the boiler and circ shut off?
  • SuperTechSuperTech Member Posts: 1,389
    I would install a L7224U and call it a day. It sure sounds like that aquastat is on its way out.
  • lmanc2222lmanc2222 Member Posts: 12,

    Neil! Exactly what I needed. I've been trying to solve this without the schematic. What I have is Fig. 4, page 4.
    A three post thermostat station (TV, W and T). What? "TV" and "T" (?) go to the thermostat. "T1" and "T2" are permanently wired at the factory just below the station on the pc board and "W" is factory jumped to "Z" (?). "Z" is jumped to "TP" (?) and there isn't a "low limit controller" nor millivoltage gas valve controller. "B1" and "B2" go to the low voltage gas valve directly. Hahahahahahah.
    I think I have to call Honeywell (if possible) to find out what this aquastat is used for. It only has a high limit wheel. It must be a 'definite purpose' control and not one for domestic heat loops.
  • lmanc2222lmanc2222 Member Posts: 12
    My final note is this. The copper heat loop itself is 1" copper which is BUSHED UP to 1 1/2" galvanized and disappears into the concrete slab floor to feed a radiant floor heat system. It returns to the boiler in two places. Hahahahahahahahahahahahahha.
    I don't care about this shoemaker installation. I care that this elderly gentleman has no sensible heat. He smiled at me while I was trouble shooting this disgusting mess and told me I was a true friend and he said that he thought he was old when he turned 90 but he can't take the cold now. God bless you, Mr. Lukac.
  • lmanc2222lmanc2222 Member Posts: 12
    Hello Neil,
    YES, indeed! It does sound like it's operating correctly . I don't think I'm explaining myself correctly. Let's see, I'm looking at a aquastat that only has a high limit wheel, no operating range. It's got me talking to myself. Boiler temperature does not go higher than 120*. I remove the circulator from the circuit and hook it up manually to 110V. Now, with the circulator out of the circuit, the boiler temperature reaches high limit. Ok, I run the circulator manually and the temperature drops to 120* (ok) but it stays there. Hmmmm. I want the circulator to turn off at the set point on the thermostat and I want the burner flame to stay on until the limit is met. Eventually I want to circulate 190* water. He only gets 120* water.
  • STEVEusaPASTEVEusaPA Member Posts: 4,353
    What you hope to accomplish is not necessarily correct, or even a good idea.
    You appear to have a simple high limit aquastat. You could bump up to a modern aquastat with circulator hold off, or you could add another simple aquastat that breaks at the set point, typically called a low limit reverse, and wire that to the circulator. Then the boiler water temp will be much higher, circulate at a higher temp, and you’ll be protecting the boiler from low temperature return water.
    I’m still a little confused as to the actual problem. If the boiler is satisfying the thermostat, that’s good, right?
    Your high limit is a safety control, not an operating control. You don’t want, nor should you need, the boiler bouncing off the high limit on every call for heat. You should only need 180/190 degree water on the few coldest days of the year.
    Let me know what if anything I am missing.
  • lmanc2222lmanc2222 Member Posts: 12
    Hi STEVEusaPA,
    I have since contacted Honeywell and they have confirmed that the aquastat needs to be replaced. The method of operation for this 8148 aqauastat is to use the thermostat as a operating control. It's the thermostat that turns the circular on and off (as usual) and when the room is satisfied the circulator is supposed to turn off and the burner is supposed to run separately until the high limit is met. Yes, it's using the high limit as an operating control and a safety. That's just how the very old aquastats use to work. There wasn't a differential adjustment many, many years ago. Remember? Maybe not.
    However, this man's boiler never reaches the high limit for some reason. The circulator runs constantly and the boiler never satisfies. It's rather puzzling to me why the water doesn't eventually heat up (in a 24 hour period) even though the circulator is running throughout the cycle. After all, it's a closed system. The water maintains 120* and the system runs indefinitely. There are no leaks. The boiler feeds directly into the return loop and just maybe this is tempering the water as it returns into the boiler rather than feed the boiler directly.
    I'm changing the aquastat out with a 4006 and going from there. I'm guessing that the new stat will hold the circulator off until the boiler reaches temperature and then turn the circulator on. I'm expecting the new stat to turn off the circulator when the boiler temperature falls below set point and use the hi limit only as an exclusive safety. It's what I did manually for a few cycles. I must admit that it is intriguing why the water doesn't eventually heat up under the 8148 system.
  • STEVEusaPASTEVEusaPA Member Posts: 4,353
    It’s possibly a combination of an undersized boiler and a large water content in the system. Plus you said you had 1 1/2” going into a radiant slab. If the slab isn’t insulated, the ground could be extracting all the btu's.
    I don’t understand why you would bother with a 4006. You’d be better off with this:
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