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Electric Boiler Sounds Like Coffee Maker (and Honeywell T9 Short Cycling)

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  • GroundUp
    GroundUp Member Posts: 1,907
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    danwheeler said:

    Thanks, @GroundUp - OK, so:

    1) Reduce glycol mixture
    2) Double check expansion tank PSI
    3) Turn down boiler setpoint to 100F
    4) If 2 and 3 don't keep PSI consistent, tee expansion tank to PONPC

    I'd probably pipe the tank to that tee you noticed. It came with my kit and just has a schrader valve on it but I don't know what it's for.

    How important is it that an expansion tank is mounted to allow air to escape from the lines running to it? Seems like if it was mounted wrong, it would turn into a dead-end air trap if it were mounted above the point where it tees into the system flow or had pipe that went up and back down again. (no flow to push the air through)

    One more question - everyone says disconnect your expansion tank before charging it. I completely discharged it before installing it and pumped it up to 12PSI but since I want to double check its pressure before going to the trouble of changing where it connects into the system, is it acceptable to just drop my system pressure to 0PSI then check the expansion tank pressure?

    Mounting is of less importance than connection point, but the idea is to keep the pipe connecting it full of water. Any moist air in the water side will contribute to corrosion, but that's not to say they CAN'T be mounted and piped another way. I have seen a LOT of 20+ year old expansion tanks mounted upside down or on the side or with goosenecks in the piping that are still working well, but the proper channel is to keep the whole water side wet. I don't think anyone ever said to disconnect the tank before charging, but there simply can't be any pressure on the water side when setting or checking the pressure on the air side. If you discharged the air side before connecting, that's probably why there's too much in it now. They come factory precharged to 12 and should remain there unless the water side needs to exceed 12. If I were you, I would just check it after you dump the glycol and the water side is at 0. Use a low pressure gauge, not a regular tire gauge that goes up to 100.

  • hot_rod
    hot_rod Member Posts: 22,131
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    The point at which the expansion tank connects to the system establishes the PONPC
    If your circulator is flowing down then you are in fact pumping away from the PONPC, it’s fine where it is.

    So the few lbs of pressure differential that the circulator adds to the system would show up as pressure increase if you had a gauge at the discharge side of the circ 

    Static pressure us what you read with the circulator off. Dynamic pressure is what you read with it running. The amount of increase depends on the pump size and the circuit connected.
    From room temperature to highest operating temperature, expect to see some pressure increase. As long as you stay 5 lbs or so below relief valve pressure, no problem. Higher pressure helps remove air, as the air bubbles get squeezed smaller and make their way back to the air purger.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • GroundUp
    GroundUp Member Posts: 1,907
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    A properly sized, installed, and charged expansion tank will maintain one pressure point regardless of system temperature. That is their intended purpose. While some rise is acceptable, it is not ideal. Doubling pressure with an already oversized expansion tank is not even acceptable.
  • nate379
    nate379 Member Posts: 37
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    I have a T9.and same issues with short cycling.

  • danwheeler
    danwheeler Member Posts: 72
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    https://forum.heatinghelp.com/discussion/comment/1743990#Comment_1743990

    Get rid of it. I switched to an ecobee and it's so much better.



  • nate379
    nate379 Member Posts: 37
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    https://forum.heatinghelp.com/discussion/comment/1744006#Comment_1744006

    NNo more short cycling?

  • danwheeler
    danwheeler Member Posts: 72
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    https://forum.heatinghelp.com/discussion/comment/1744907#Comment_1744907

    Problem solved for me after dumping the Honeywell T9 and installing an Ecobee. The Honeywell T9 has zero "swing" and is obnoxious if you're anywhere you can hear your equipment turning on and off. I think it would have worn out my boiler relays if I left it in and the noise was driving me nuts. I'm going to install that T9 in my other home with forced air, I think it will be a better fit.

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