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Fried aquastat

T. J.
T. J. Member Posts: 47
edited October 2017 in Thermostats and Controls
I have a Honeywell L8148E1265/U controlling my New Yorker boiler on my hydronic heating system (single zone with a mixture of baseboards and fan/coil convectors).

When I tried to start it up for the first time this season, the thermostats turned on the convector's relays and sent voltage to the aquastat, but nothing happened on the boiler end. The burner didn't fire up, the circulator didn't turn on and the damper didn't open. I thought I smelled something burning ever so slightly, so when I took off the cover of the aquastat, sure enough, it looked like the circulator relay burned up and must've taken everything out with it.

I have two questions:

1. In your opinion, is replacing the aquastat something a homeowner whose performed some plumbing and wiring in the past accomplish himself? I know I don't have to drain the boiler or anything, but is the immersion well setup complicated procedure?
2. Is it possible that a stalled rotor or something else wrong with the circulator could have taken out the aquastat and I actually have two failures? If so, what's a safe way to test the circulator? It's a Grundfos 15-42F.

T. J.


  • unclejohn
    unclejohn Member Posts: 1,759
    If you can get the exact same aqua stat down to the last number it will be a wire for wire change out. Don't normally see that kind of failure so something else most likely wrong. If you don't get a normal start up with in 10 seconds of power up shut it off and call some one.
  • Alan Welch
    Alan Welch Member Posts: 255
    Any possibility water from above dripped on the control? A major cause of control failure. To check the circulator, with power to control off,disconnect wire from terminals c1 and c2. Then power those wires carefully from another source . The circulator should run normally.
  • T. J.
    T. J. Member Posts: 47

    Any possibility water from above dripped on the control? A major cause of control failure.

    Wow, I never connected the two, but we did have a 10 gallon fish tank leak and drain out overnight a couple of weeks ago in the living room above which made it's way through to the basement, but the leaking seemed to be confined to a couple of feet away and on the other side of the boiler. I guess it's possible that some of the water could have wicked along the beams above in the basement and dripped on it a bit, but I didn't see any evidence in that area at the time. Not beyond possibility, I'd imagine, though.
  • T. J.
    T. J. Member Posts: 47
    Regarding replacement. I don't see a set screw at the bottom of the immersion spud as seen in the shot I took of my setup (looking up from below, aquastat on right and the supply elbow in the center which contains the immersion well).

    The instructions for the 8148 aquastat depict a set screw to remove the old unit. Does my setup indicate that I need to drain the system and remove the entire well?
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,776
    The actual well, yes. If you can isolate the boiler, and turn off the water feed, you'll have to drain it to below the well to change it (if it's leaking). Or if you go with an electronic control, you may have to change it if required to allow the low water cut-off to work.
    EBEBRATT-Ed Member Posts: 12,314
    I think the screw your looking for may be in your picture. if you replace the control with the same model you do not have to drain the boiler or change the well
  • SeymourCates
    SeymourCates Member Posts: 162
    Ed is correct. You do not need to change the well. Just turn that hex screw in the photo and the aquastat will release from the well.

    One of the primary failure modes of the HW controls is the failure to properly wrap the wire at least 3/4 turn beneath the screw head. Many installers just catch the side of the wire (because a full wrap is difficult and time consuming) and the heat buildup beneath the head of the screw eventually takes out the entire control.
  • BobC
    BobC Member Posts: 5,317
    If you can put that old control apart and see if it's a printed circuit card. If it is you may find a faulty solder joint caused overheating and failure.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
    HVACNUT Member Posts: 4,654
    The 5/16 hex bolt in your 2nd pic is what loosens the aquastat from the well. It's a clamp inside so you might have to give it a little smack to pop it free.
    Take a pic of the wiring so you know for sure where everything goes.
    Looks like someone used pump pliers instead of a box wrench to install the well. Yuck.
    Do you have a low water cutoff?
    If not, look into the Hydrostat 3200 Plus. Then you will need to change the well, and use a Hydrostat well.
    The Hydrostat aquastat will give you low water cutoff protection, has boiler reset, or an optional ODR.
    Even if a LWCO is already there, you can use the 3200 Plus and NOT change the well. There's a lot more room in there to wire it up as opposed to the L8148.
  • T. J.
    T. J. Member Posts: 47
    That screw indeed released the unit from the spud. On the new unit, I coated the bulb with the thermal grease and crimped on new spade connectors with self-sealing heat shrink tubing on a lot of the wiring as some of the old connectors looked a bit flimsy.

    Here's what it looked like after I sewed everything back together....

    Everything works great and I have heat! Thanks to all for the advice. BTW, I took apart the old aquastat. You can see the damage....

    EBEBRATT-Ed Member Posts: 12,314
    good job!!