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Aquastat Relay

Alan (California Radiant) Forbes
Alan (California Radiant) Forbes Member Posts: 2,753
edited April 4 in THE MAIN WALL
For some reason, I'm not getting power to the ignition control module on this Hydrotherm boiler. All the safeties (spill, rollout and hi limit) on both legs of the transformer are closed, there's power at B1 and B2 and the light is on on the vent damper. Can I just bypass the vent damper and wire B1 and B2 directly to the ignition control module? I'd make sure the safeties are intact and lock the vent damper open.
If yes, do I need to determine which terminal (B1 or B2) is which? Just for interests sake, how do I do that? Whichever one shows power to ground is "R"?


Often wrong, never in doubt.

Comments

  • HomerJSmith
    HomerJSmith Member Posts: 1,286
    1 & 2 operate the Vent motor- 3 & 4 send power to the ignition module. Alan, you're really smart at this stuff. I'm surprised that you are asking. What is the voltage between 1 & 4 ? Should be 24 V. Between 3 & 4 is a micro switch. Jump 3 & 4 and see if you are getting 24 V at the ignition module. If so just jump 3 & 4 and block the vent open removing power to #1 or just replace the micro switch.

    You don't want to eliminate any of the safety devices. Happy Easter!

  • Yeah, yeah. I'm smart until I'm not.

    I want to eliminate the flue damper entirely. I don't like them because I don't understand them.
    Often wrong, never in doubt.
  • HomerJSmith
    HomerJSmith Member Posts: 1,286
    edited April 5
    Yes, you could connect B1 to the 24 V on the ignition module and B2 to the 24 Grnd, but you would eliminate the safety rollout switch.

    However, you could connect B1 to one side of the rollout switch and still have it in the circuit. Never the less, jumping #3 & #4 would accomplish the same thing.

    If you're not getting voltage at the 24 V on the ignition module, check the continuity on the rollout switch. It may be open. If it is open, the vent motor may not be opening the vent and the flame has nowhere to go except out the front of the fire box. The vent damper usually has an indicator telling you the position of the damper-- open or closed.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,753
    edited April 5
    Thanks for responding, Homer.

    I would keep all the safeties on board and just bypass the flue damper.

    What does the "Z" terminal on the aquastat relay do?

    If you're not getting voltage at the 24 V on the ignition module, check the continuity on the rollout switch. It may be open. If it is open, the vent motor may not be opening the vent and the flame has nowhere to go except out the front of the fire box. The vent damper usually has an indicator telling you the position of the damper-- open or closed.
    That's really smart of you to say that. It's my first time on this job as the owner lost patience with the previous tech. As I found it when I showed up, the flame rollout switch wires were jumpered and the fusible link was blown (no continuity). The previous tech. had replaced all the burners and the burner door since they were all fried and the new burner door already had heat damage.

    I usually don't see these Hydrotherm boilers soot up, especially on a radiator system, but the first order of business is to clean the HX and then to get the boiler fired.

    The guy before me told the owners they needed a new boiler.

    As far as the Johnson Controls flue damper, it's stuck open and the light is on, but I don't think the end switch is closed. As you can see on the picture below, there are three relays surrounding the stem of the damper and I don't know which one is the end switch.





    Often wrong, never in doubt.
  • HomerJSmith
    HomerJSmith Member Posts: 1,286
    edited April 5
    Since you have 24 V at B1 & B2 at the aquastat, it means that the relay ( K2) in the aquastat is functioning when the thermostat calls for heat. It is an AC circuit, but consider B1 as a powered lead and B2 as the grounded lead. B1 would go to the 24 V on the ignition module and B2 would go to the 24 V grnd terminal.

    Z on the aquastat is connected to one leg of the secondary on the aquastat transformer sending 24 V to #2 on the damper. #1 is connected to B2 the other leg of the aquastat transformer. That completes a circuit when K2 relay closes, activating the damper motor.

    Between Z & TV should be 24 V.

    I don't have a schematic for the damper, but I see a capacitor, resistors and diode, a relay and micro switches and synchronous motor on the board. Usually, I think, when power is disrupted to the motor, it defaults to an open position because the damper is spring loaded.

    See this:
    https://forum.heatinghelp.com/discussion/179453/old-and-discontinued-mizer-johnson-control-m35ba-1-damper-control-replacement

    and:
    http://www.graycoolingman.com/uploads/1/0/6/6/10667336/johnson_controls_m35be_vent_damper.pdf
    Alan (California Radiant) Forbes
  • HomerJSmith
    HomerJSmith Member Posts: 1,286
    edited April 5
    The Red & Blue wires attached to the molex plug at the vent damper are #3 & #4. Pull off the molex plug and jump the Red & Blue wires and leave it disconnected from the vent damper board.

    The damper should have defaulted to the open position and you should get power to the 24 V connection at the ignition module after you replace the rollout switch (thermo fuse).

    When you get it running check the flame and draft.
    Alan (California Radiant) Forbes
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