Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Wiring Mystery

Hilly Member Posts: 428
We show up today to fix a broken aquastat as the domestic indirect was putting out almost 200°F. Thermostat on the TT - Phase III was gone too.

Here's the problem.
Boiler is on a triple acting aquastat and the TT are jumped out. It appears the heater always runs on one big loop and each unit has its own zone valve. We get there and the maintenance just had the system pump disconnected. In my diagram you'll see 2 wires go from the "ice-cube" relay to the aquastat. When I switch everything over I can get the indirect to fire just perfect. I have no idea what the point of the ice cube relay is here. How can those wires be connected in a way that something is achieved. Either I'm missing something or the last person put in something that had no purpose so disconnecting the 2 wires was his solution. These icecubes always make my head spin in circles when troubleshooting.

Thanks in advance.


  • Hilly
    Hilly Member Posts: 428
    Unless maybe it was once wired to the ZC to somehow give domestic priority? That's all I can think but I'm not certain how exactly.
  • Hilly
    Hilly Member Posts: 428
    I had to take a break and start over.

    I think the below is what is happening.

    The ice cube is a priority. Basically c1 is hot c2 is neutral.

    C1 -> power to system pump
    C2 -> neutral to ice cube

    Ice Cube
    Return wire goes to system pump (splice undercover of aquastat)

    The ice flip flops

    So when the indirect energizes the neutral "breaks" on the system pump preventing it from running while the indirect calls for heat.
    HVACNUT Member Posts: 5,870
    Start by designating numbers to your relay drawing. The coil is 2 and 7 which according to your drawing is the bottom left and bottom right. The unused pins on your drawing I assume are the N.C. contacts (4 and 5). Other than that, I'm lost. The relay diagram is CW in numerical order. Can you draw yours the same? Oh, and can you make it a circle too?
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    If you just write the numbers of the terminals that those wires on the relay are landed on we can figure this out.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!