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Low limit not turning on boiler

shadowdoc2shadowdoc2 Member Posts: 5
I have old oil furnace with tank-less coil for hot water. HWBB throughout the house. Recently the call for hot water from using hot water is no longer triggering the furnace to fire up. The call for heat works fine as long as the temp does not go below the low limit set point. I've found a work-around when we need to shower, and that is to kick my thermostat up a couple degrees, which quickly causes the furnace to fire up, and then we enjoy our scorching hot water in the shower. This isn't so bad when its really cold out, but as it is getting warmer, I won't need the heat as much. Why won't the drop in water temp trigger the furnace all of a sudden?

Comments

  • icesailoricesailor Member Posts: 7,265
    Low Limit Not Turning On:

    Either the control has failed or the High" and Low (Operating control) are set too close together. They must be at least 20 degrees apart. For a start, set the "HI" at 180 and the "LO" at 160 and see what happens.
  • shadowdoc2shadowdoc2 Member Posts: 5
    Low limit not turning on boiler

    That is exactly how it has been set and working fine for the entire year. Now as long as there is a call for heat before the temp drops below 160 degrees, the boiler works fine. If there is no call for heat and the temp drops below the 160 or if we use the hot water to say say shower, a drop in temp of any degrees will not cause the boiler to kick in.
  • billtwocasebilltwocase Member Posts: 2,385
    temps

    Do you have a tempering valve on the coil? If you do, try higher temps. 170/190. What is the temp gauge reading, and where is the control activating the burner? What control model do you have? Pics?
  • shadowdoc2shadowdoc2 Member Posts: 5
    edited April 2011
    Low limit not turning on boiler

    It's an old system, installed in 1963. I know I should replace it, but it has served me well with not a crazy cost. The pics are of the aquastat and gauge. There is no temerping valve I can locate. Raising the limits does not change how it operates. Thanks for the replies thus far.
  • billtwocasebilltwocase Member Posts: 2,385
    looks like

    an L8024C. When you raise the limits, no response? I would check for power at both screw terminals on the temp block where the solid metal jumper is. It becomes a cold start control when there is no jumper, or power there. Can you hear a click when you raise the low limit above the water temp reading according to gauge? Was the 170 temp on the boiler from a heat cycle? Those controls rarely went bad, but it does have a few years under it's belt. If you have a volt tester, I would raise it and check for power at B-1.  would also have a licensed professional check and replace it if need be. 
  • shadowdoc2shadowdoc2 Member Posts: 5
    edited April 2011
    Low limit not turning on boiler

    You're good. :-) It is a L8024C. I tighten all the wires, as 2 were a little loose, B1 being one of them.



    I went back and played with the limit switch and realized that there is a lot of 'play' in the setting switches (hi/lo). I turned the heat off at the thermostat and slid the low limit almost all the way down. I then let the boiler temp drop to 160 and slowly moved the low switch up and at "about" 160, the boiler kicked on. Did the same to get the high to shut it off at 180.



    I put the thermostat back on to heat and LUCKILY, the system has been working fine since yesterday. Not sure if this makes sense or I just got lucky. lol



    I sincerely appreciate all your help. I just love trying to solve a mystery and learn something at the same time. M
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