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  1. #1

    25V transformer intermittently cutting out? 3-wire hot-water radiator boiler.

    I replaced a two-wire battery powered tstat with an Hvac powered one (without battery back up). So the 'Common' line was unused until now.

    After about 10 minutes of calling for heat, the tstat loses power and turns off and comes back on a minute or so later. It doesn't seem to be a tstat issue. last time it went dead, I pulled it off and checked the wires with a meter, it read ~3V or less for a while and came back up to normal.

    This only happens during heat-call and not other times. What's going on here? Is there something that kicks in after a few minutes and chokes the tstat?


    Here is how the lines are connected from the boiler to the tstat:

    TR -> Common
    TH-TR -> Return
    TH-> W (heat call)

    TIA

  2. #2
    Join Date
    Jan 2008
    Posts
    2,025
    From your wiring description, I'm thinking you're in over your head.
    We can't give DIY advice.
    I would call for service.
    "Hey Lama, hey, how about a little something, you know, for the effort." And he says, "there won't be any money, but when you die, on your deathbed, you will receive total consciousness." So I got that goin' for me, which is nice. - Carl Spackler

  3. #3
    2old2rock,

    lol, how ironic, I earn my living designing hvac products. Figured that'll qualify as not being in over my head. Should I have included a schematic diagram? pulled the wiring the labels from the Gas Valve. Here's a picture.

    Name:  IMG_0667.jpg
Views: 947
Size:  37.1 KB

    It is a bit confusing for me, I haven't worked with too many of the old-school boilers, hence the question.

  4. #4
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,013
    Explaining what could be causing the loss of power to your new thermostat would be giving DIY information which isn't allowed by site rules.

    I would also suggest that you call in someone proficient with boilers to take a look at your system. If the power to the thermstat is going away after only 10 minutes of the boiler running and then comes right back on you've got bigger problems that they should be easily able to find. While they're there, ask lots of questions and get schooled up on the "old-school" boilers.

    Just curious, but what kind of HVAC equipment do you design?
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  5. #5
    firecontrol,

    I see. So it was about DIY (now understand the meaning, thanks to you), not necessarily about the wiring diagram.

    I'm afraid you were more helpful than intended (thanks, honestly). Turns out the High Limit on the aquastat was set to 160 which was kicking in and pulling the power out of the transformer. The old battery powered tstat must have ignored this for years.

    Would asking "what is the best Aquastat High Limit setting?" still be DIY?


    (ps. I can not answer your question on-line, subject to comp. policy)

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,085
    What you think is the problem, isn't.

    Next time you have your boiler serviced, ask the tech to correct it for you.Its a simple thing to do.
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    How many times must one fix something before it is fixed?

  7. #7
    beenthere,

    What I think is the problem is, is somehow with no air in the lines, valves open, and circulator pump running, the 100K BTU boiler can't get rid of the heat fast enough with only 4 rads. And if I can't see the 'simple thing to do' then tech call it is. I would have liked to wait and ask the tech to replace the unit with a hi-efficiency of the right size. This feels like asking a tech to fix a modem on a 386.

    Eitherway, thanks for dropping the hint, got me further.

  8. #8
    Join Date
    Aug 2001
    Location
    Pavilion, NY
    Posts
    2,141
    Is this system zoned? White Rodgers zone valves perhaps?
    ...

  9. #9
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,557
    Quote Originally Posted by RMando View Post
    2old2rock,

    lol, how ironic, I earn my living designing hvac products. Figured that'll qualify as not being in over my head. Should I have included a schematic diagram? pulled the wiring the labels from the Gas Valve. Here's a picture.

    Name:  IMG_0667.jpg
Views: 947
Size:  37.1 KB

    It is a bit confusing for me, I haven't worked with too many of the old-school boilers, hence the question.
    I think you misunderstood what he meant.

    We have a vetting process here, and if you qualify as a Pro, you can post in the Pro section and get a lot of technical help.

    We can't post what you need in open forums, and certainly not in the AOP section.

    Thanks.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  10. #10
    Quote Originally Posted by timebuilder View Post
    I think you misunderstood what he meant.

    We have a vetting process here, and if you qualify as a Pro, you can post in the Pro section and get a lot of technical help.

    We can't post what you need in open forums, and certainly not in the AOP section.

    Thanks.
    I agree, this question doesn't belong here in AOP and it is DIY as noted. Will look into the pro section for the future.

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