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Weil Mclain Ultra 230 Series 1 Boiler - Outdoor Temp Sensor

6crnbnh Member Posts: 4
I'm thinking of adding the outdoor temperature sensor to my Weil Mclain Ultra 230 boiler. The only question I have is that this unit, when wired, was not wired to take advantage of the DHW connections. We have an indirect water heater in which a coil runs through the center of the unit with heated water from the boiler that heats the water in the tank. It is wired as a zone similar to our 2 air handler zones and 2 radiant heat zones.

I am curious if adding the outdoor temperature sensor will affect the heating of the water in the water heater as the outside temperature is monitored by the unit and the fire rate and boiler water temp is modulated. This is supposed to make the unit more efficient than it already is and I have already set the parameters as required (P4 thru P8).

We have 2 Taco relays, one for each radiant heat zone (2 zones total). These 2 relays are wired into a 3rd, larger relay that contains 1 green and 4 red LED's. Each of the 4 red LED's applies to a zone. 1 for the 1st floor air handler, 1 for the 2nd floor air handler, 1 for either radiant zone when 1 or both Taco relays for the radiant heat are calling, and the last LED is for the DHW.

I did note in the manual that when the actual DHW aquastat connections for this boiler are used, it is a priority setup, meaning that when the water heater is calling, space heating is disabled. Probably why it was not wired with that configuration and instead the water heater was wired as just another zone.

Any input would be greatly appreciated!


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    A few more questions.....

    When you say you want to add an outdoor temperature sensor, which relay or control do you want to connect it to?  You could wire it like the book states, and probably will have to when you use ODR.  This way when you have a DHW call, the temp will ramp up to the DHW exchange temp.  It will disable the other zones (priority), but usually there is a something built into the control that will only disable it for a short time.  Unless you have some major DHW usage, on the coldest days of the year, you'll never notice  You could also wire the DHW thru the Taco, as non-priority or priority, but then you'll probably get too low of an exchange rate (boiler target temp) to make enough DHW.
  • 6crnbnh
    6crnbnh Member Posts: 4
    OTS & DHW Current Wiring

    I want to add the outdoor temperature sensor to ODS 1 & 2 per the low voltage field wiring connections in the manual.  This is located on the top, back of the boiler behind the intake and outlet pipes.

    My system was not wired to use DHW 3 & 4 per the low voltage field wiring connections in the manual.  The DHW is presently wired through the main Taco relay as Zone 4 (4 zone LED's on the Taco relay) and it is definitely non-priority.  This is my concern because as the outdoor temperature increases, I am assuming the boiler target temperature will be set lower as the boiler cannot differentiate between a space heating zone (Zones 1 thru 3) and the DHW zone (Zone4).  If this IS an issue, I'm curious if there is another way to wire the DHW zone so it is non-priority but NOT affected by the outdoor temperature sensor.  If not, then this probably explains why the outdoor temperature sensor was not originally installed.
  • Paul48
    Paul48 Member Posts: 4,469

    Assuming it has the U-Control. You would use terminals 4 and 5(demand 1) for DHW. It would be given priority, with a set temperature, and would not be affected by the ODR. Your space heating requirements would be demand 2 and or 3.Read the manually carefully.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Assuming it has the U-Control.

    Trouble is, the Ultra series 1 and series 2 did not use the U-Control. W-M started using the U-control with the Series 3. It is much more flexible than the PhD controller used in the Series 2. I have no idea what went into the Series 1.
  • 6crnbnh
    6crnbnh Member Posts: 4

    As much as I appreciate the responses so far, I'm not sure my initial question was answered?  Is it possible to use the ODS with my present configuration or will it affect the DHW as it is simply wired as another zone from our Taco SR-504?
  • 6crnbnh
    6crnbnh Member Posts: 4
    edited February 2012

    Is it possible to convert a Series 1/2 Ultra boiler from PhD to U-Control?  Series 1 is definitely PhD.
  • Paul48
    Paul48 Member Posts: 4,469

  • MIG
    MIG Member Posts: 1
    Temp Sensor Not Working

    Hello - we have this boiler as well. It has been working fine since some initial installation issues about 5+ years ago.  DHW is working fine. 

    Tried to turn heating on last night but getting an outdoor temperature lockout.  The outdoor temp is displaying as 127 degrees on the boiler display screen (it's really around 40 degrees).  Wiring to the outdoor sensor seems intact. 

    Sensor seems to be an easy, inexpensive replacement.  Does anyone have any other thoughts on things to check before doing this?

    Thank you!
  • Tom_133
    Tom_133 Member Posts: 884

    To get heat just remove the two wires off the back of the unit, or just one. If the boiler fires right up and goes back to normal great. Than you can test the resistor in the outdoor sensor or replace it. Test it by putting a lead from your electrical meter on to each of side of the resistor and checking the ohms resistance. It will give you a number and in the manual of the boiler Weil Mclain gives a chart with what the ohms will be at given temps if it doesnt match the sensor is bad, replace it.

    If the boiler doesnt go back to normal when you remove the outdoor sensor than it will probably require a service call.
    Montpelier Vt
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