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Thread: Bit of an electrical Gremlin on an older boiler system.

  1. #1
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Default Bit of an electrical Gremlin on an older boiler system.

    Hey guys I got called out to a boiler today that wasn't working properly.

    So I get there and see it's an older (~13yrs) Weil McLean with what is basically a fan-control relay controlling it. (The standard ones with RWYGC).

    Anyway the thing was basically an electrical nightmare looking like a rats nest. So I began to trouble shoot and it turns out that the fan-control was shot. I hooked it up exactly as it was but the boiler did not fire.

    So my troubles began.

    The system has 2 pumps, and 4 zones. It's all in floor heating and being an older natural draft boiler it would appear that the 2nd pump is designed to keep the boiler hot with a primary loop and the in floor taking off that main loop. There is also a mixing valve on the return side of the infloor loop(s).

    I should also note that when I got there the control-relay was making a very loud chattering sound. Like it was shorting out. This is why I changed it.

    So after tracing out my wires and checking for power it would appear that the zone valves are wired correctly with the end switch coming back telling me there is a call for heat. This goes to G on the control relay. Once G gets power it trips a relay built into the control relay (DUH) and brings on the pump feeding the infloor. The pump for what looks to be the hot loops looks as though it's designed to come through another relay that is tripped by 24v as well.

    Y gets the start of the safety circuit which leads to the gas valve, then ofcourse the gas valve is ran back to C on the control relay.

    W has nothing.....

    R obviously is giving out power to all zone valves and end switches and thermo-stats.

    C is accepting the common side of the zone valve motors and the and the gas valve.

    The boiler is also equipped with a power damper. It has 4 wires, (YRGB I believe). Obviously one is power for the motor, one is common, and the other 2 are for the end switch. Does anyone know which is which off the top of their head?

    Also how would you wire up the pumps to trigger to come on? I should note there is a high limit just off the top of the boiler as well as (what I am assuming is) a control limit for the in floor loops.

    Also for some reason I seem to be getting a constant 24v coming back on a wire and I can't figure out for the life of me what it's for. By coming back I mean from the zone valves/end switches.

    Because of some electrical gremlin I can't find I am basically going to rewire it tomorrow. It'll be easier to start over then try to figure out what's wrong with the damn thing.

  2. #2
    In the Trades Wally Hays's Avatar
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    From the instructions - wire the boiler as shown.

    Get hold of a Taco ZV controll or Tekmars or Argos.

    Wire the zone valves and thermostats to the new control
    Use the dry end switch contacts to call the boiler
    Perception is 3/4 of reality

  3. #3
    Plumber jimbo's Avatar
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    QUOTE: Also for some reason I seem to be getting a constant 24v coming back on a wire and I can't figure out for the life of me what it's for. By coming back I mean from the zone valves/end switches


    "coming back" is possibly a misnomer. If you have hot on a line that is not connected directly to the 24 V hot, it can mean that you are on the return side of a coil, but the path for current is not complete, so the votage drop across that coil or other load is zero. Another way to think about it....when trouble shooting such circuits, be it 120 or 24 volts, you will read full source voltage across an OPEN CIRCUIT. Look for a loose wire, or another switch or relay contact that is not making.

  4. #4
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by Wally Hays View Post
    From the instructions - wire the boiler as shown.

    Get hold of a Taco ZV controll or Tekmars or Argos.

    Wire the zone valves and thermostats to the new control
    Use the dry end switch contacts to call the boiler
    The home owner will not want to pay for an external controller and the time it will take to wire it up.

    Thanks Jimbo I'll look into that.

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