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Aquastat L8124A no 24v

BGYMR Member Posts: 3
edited April 2019 in THE MAIN WALL
First time post, but I've been lurking! I spent some time researching my issue, but couldn't find an answer.

I live in PA, and we had a warm weekend, so my New Yorker boiler didn't work much over the weekend. Well, when it got cold again on Monday, it wouldn't come on. Hmmmm so I started looking at it. The boiler also heats our domestic water, and that was hot. When we moved in I switched out the oil burner for a Carlin gas unit, and it's been working great. Being that we had hot water, I knew the gun wasn't the issue. We have two zones in the house, one we never use, it's the attic. But when I turned that thermostat on, it fired up no issues. This led me to the Aquastat that controls the entire house (minus attic).

I started searching online, and sure nuff, I was in the right area. My thermostat is a Nest and it showed that it wasn't getting power on the white and red wire. My meter confirmed that there was no power at the Nest (upstairs) or at the terminals inside the Aquastat. (yes I had it on AC). Out of semi frustration, i whacked gently the Aquastat, and wala! It fired up, heated my house until Wednesday. Well, I'm back here, it's stopped working again.

Wednesday night out of a panic I ordered a transformer, it will be here today. But further reading suggested that these transformers are usually the last thing to fail in the Aquastat.

I would like to get your input, what to check. The solder joints look ok. I have 120vac coming in. If I move the relay by hand, it fires up and then stops after 3 seconds. Am I crazy for wanting to replace the transformer, I didn't find one post on this anywhere, but seems simple enough.



  • pecmsg
    pecmsg Member Posts: 4,193
    I hate NEST

    Change the stat!
    BGYMR Member Posts: 3
    Ok, good suggestion, I'll do that. But any help with the Aquastat?
  • Jamie Hall
    Jamie Hall Member Posts: 21,541
    Yes. Change the aquastat while you're at it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,257
    Agree with the above.
    You should change the aquastat to a modern one, and you could add a transformer to power your nest, although most professionals seem to agree that the nest is problematic.
    BGYMR Member Posts: 3
    Thanks for the suggestions.

    By a modern Aquastat are you saying to get away from analog and go to a digital one? I'm assuming that the one on my boiler is original, and if I get the same span out of a new analog Aquastat, I'm probably approaching a boiler replacement anyway.

    Do you guys not repair the aquastats because you do this as a business and it's simpler to swap it out, or because you figure it's only a matter of time before something else gives out on it?

    What number stat should I put in instead of mine? I called a local HVAC supply shop, they said a new L8124A is $239, a bit higher than online options, but I like supporting local.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,257
    Yes digital.
    I don't repair them because in my mind, it's a UL product and repairing/fixing them would put the liability on me if they failed and a disaster occurred. Plus they are an operating and safety device.
    I imagine others feel the same way.
    Plus there's no warranty. They are all pretty standard so it's never a case of not having one to replace a failed existing.
    As far as longevity, I doubt any new one will last as long as the old one-mechanical or electronic. But the electronic one has more features (like LWCO, economizing & circulator hold off), is more accurate and could save you some money.
    EBEBRATT-Ed Member Posts: 13,810
    Before you scrap the aqustat disconnect the thermostat wires going to the nest. Jumper the stat wire at the aqustat and see if it runs. It should start and stop with the jumper
    HVACNUT Member Posts: 5,258
    edited April 2019
    The main zone worked for 2 days after "wala" so I dont think it's the transformer.
    When you measured voltage was the Nest calling for heat at the time? It will read 0 volts across TT with a heat demand, 24v without a heat demand. TT is just a switch, not a source.
    Is the attic zone relay wired to ZR,ZC on the aquastat?
    My guess is failing erratic 1K1 and 1K2 contacts.
    Forget replacing parts. Do like at @STEVEusaPA said and update to a modern aquastat.
    The Hydrostat 3250 Plus is nice.
    A resistor can be wired in series for your (YUCK) Nest.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,257
    Side note: a 3250 in this situation only because its a gas power burner, similar(ish) in wiring to an oil burner. If it were a regular gas boiler, 3200.
  • unclejohn
    unclejohn Member Posts: 1,833
    Does your system have a vent damper?