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Boiler temp not reaching aquastat

DJD00DJD00 Member Posts: 6
I’ll start by saying I recently had my boiler converted from Oil to gas . And i knew with the oil burner that the water temp would reach the temp set on the aquastat and then shut off which is 180. But after gas burner installed, right away I noticed water wasn’t get much over 150. But the aquastat would respond if I turned it up that water temp would warm up by whatever amount I increased it. Could there be an problem with the aquastat or temperature gauge? The person who installed the gas had came back for some other issue and I asked about this and they didn’t seem to notice any issue.


  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,058
    The temperature on your gage should read the same as the aqaustat setting. But those setting are sometimes not that accurate. I wouldn't be concerned if it is within 10 degrees as long as the aquastat responds as it should.

    The fuel, oil or gas has nothing to do with the aquastat. The tech that installed the burner may have adjusted something
  • ZmanZman Member Posts: 5,831
    It could be something as simple as a sensor not being pushed as far into a well.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • DJD00DJD00 Member Posts: 6
    It’s more like 25-30 degrees off, aquastat is set to 180 (differential wheel is set to 5) and burner shuts off around 150-155.
  • DJD00DJD00 Member Posts: 6
    Also, while aquastat is at 180 and temp gauge read 150, if I turn aquastat to 190, the temp will also then read 160 before shutting off the burner so does if I turn aquastat to 200 the gauge reads 170. So questing aquastat is working fine since burner is shutting off at a temp. Guess the temp gauge could need replacing?
  • Intplm.Intplm. Member Posts: 1,158
    Like @Zman said. And, It could be as simple as your emersion bulb on the aquastat or the immersion well or both. It needs to be in all the way and the capillary tube needs to be undamaged. (Of course.)
    Heat sink paste that looks like gray never seize should also coat the bulb too if the directions call for it.
  • LeonardLeonard Member Posts: 903
    Was the aquastat or temp gauge replaced or new one added?
  • JellisJellis Member Posts: 202
    Make sure you dont have a bad gauge as well.
  • DJD00DJD00 Member Posts: 6
    @Leonard Nothing has been replace other then the burner, so if I turn he aquastat up it does seem to get warmer but temps don’t match. Guess I should have someone check out the temp gauge
  • Intplm.Intplm. Member Posts: 1,158
    And have the aquastat checked too.
  • HVACNUTHVACNUT Member Posts: 3,370
    If it's an L4006A then there are better aquastats.
    Was a chimney liner and spill switch installed?
  • DJD00DJD00 Member Posts: 6
    edited March 2019
    Yes it a honey L4006a. In that case the temp gauge be correct but the aquastat just not working properly. a chimney liner was installed but maybe 3-4 years ago
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,058
    Could be the gage. Could be the aquastat. I would guess the gage but I could be wrong.

    Measure the pipe supply temp with a thermometer. Do you have an oven thermometer you could tape it on a pipe tight as you can and wrap some rags or something around it to insulate. Won't be great but may give u an idea
  • DJD00DJD00 Member Posts: 6
    @EBEBRATT-Ed I your suggestion using oven thermometer, put it under pipe insulation I’m using on the pipe in the basement. And when the burner shut off, it read basically same as temp gauge in boiler (160F) and aquastat is at 190. Guess that says aquastat is faulty.
  • LeonardLeonard Member Posts: 903
    edited March 2019
    I'ld compare pipe temp to boiler guage in middle of a long circulator run, say of 10- 15 minutes. With baseboards cold when room thermostat calls for heat my boiler gauge temp drops FAST as the circulator runs for only 2 minutes and boiler temp drops ~30 degs ( it's all that cold water coming into furnace from baseboards)

    I've also got differences between my aquastat and boiler temp guage. I just chalk it up to 60 year old gauge has likely drifted, or aquastat is not all that accurate.

    One thing I accidentally found out when gradually turned up aquastat for real HOT DHW was I eventually found point where few steam bubbles noisily rose up a pipe. Then I knew actual temp was over 212 deg F.
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