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Outdoor Air Reset Issue

akaDigger
akaDigger Member Posts: 23
edited November 2022 in THE MAIN WALL
Lochinvar WBN50 W/DHW/radiant floor, installed in 2008. Annual service performed by me (installer/homeowner) a week prior to issue arising. The service was as routine as any in the past. A thorough cleaning and inspection.

I'm having an issue with the outdoor reset. The boiler is not firing due to perceived high outdoor temp. For example, this morning when it was 47°F outside, the boiler display read 62°. The thermistor that came with the boiler, when tested with ohm meter, tests exactly as it should. These readings were tested at the boiler disconnected from the board.

This happened last week too. Then, I tested the thermistor on the bench. All good after soaking it in the refrigerator to get an exact known temperature. After reinstallation, the boiler display showed the correct outdoor air temperature. For several (warm) days after the boiler continued to display the correct OAT.

Then, today, a cool morning I again have an incorrect OA temperature reading.

DHW works as it should.

At this point I'm afraid the Control Module may be acting up.

Thoughts please.

-Dan, aka Digger


Comments

  • Jamie Hall
    Jamie Hall Member Posts: 20,501
    More likely the sensor or something in the wiring -- you mention damp and cool. Wiring doesn't like that... check all your connections.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 18,269
    Is the sensor seeing sunshine or heat from a dryer vent or some other influence.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • pedmec
    pedmec Member Posts: 713
    Is the OA still in its plastic housing and not being affected by the sun? make sure its in the shade.

    To do an accurate test give the sensor an ice bath. put it in a bowl with ice an water. that way you know the fluid temperature is exactly 32 degrees. but wrap the sensor to prevent it from getting wet, just to safe.
  • akaDigger
    akaDigger Member Posts: 23
    OA sensor is installed properly in its original case on the north side of the home. It has worked as it should for fourteen years.

    Again, the sensor and its wiring test fine.
  • hot_rod
    hot_rod Member Posts: 18,269
    The sensor is the least expensive part to replace. The control board swap $$ would be my second choice.

    You can see all the wiring, connections, any splices?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Zman
  • akaDigger
    akaDigger Member Posts: 23
    When I first saw the erroneous reading I was almost elated as surely it was an easy fix. But I did the testing and have ruled out the sensor and wiring. Sensor case shows some fading but the sensor is clean and dry, looks new. No splices in wiring, I installed it myself.

    Looking at a cost of between $550 and $650 depending on the part# which we currently are not sure of. Lochinvar support is pretty busy today. It is Monday and peak season 
  • pedmec
    pedmec Member Posts: 713
    In the knight service manual at 47 degrees you should be getting an ohm reading of 21,760. That's interpolating between 40 and 50 degrees.
    akaDigger
  • HomerJSmith
    HomerJSmith Member Posts: 1,927
    edited October 2022
    Where did you measure the ohm reading? The terminal wires at the control board is where to measure. Always make sure the wires are secure in the terminals when done.

    Go into the installers programing (password 5309) and check the outdoor warm weather shut-down value.
  • akaDigger
    akaDigger Member Posts: 23
    edited November 2022
    pedmec said:

    In the knight service manual at 47 degrees you should be getting an ohm reading of 21,760. That's interpolating between 40 and 50 degrees.

    I just retested it again, DISCONNECTED from the board, 16.3k ohms @58°. That is correct according to the service manual.
  • akaDigger
    akaDigger Member Posts: 23

    Where did you measure the ohm reading? The terminal wires at the control board is where to measure. Always make sure the wires are secure in the terminals when done.

    Go into the installers programing (password 5309) and check the outdoor warm weather shut-down value.

    With the wires secure in their terminals on the board, probing the terminals, I get only 150 ohms.
  • akaDigger
    akaDigger Member Posts: 23
    edited October 2022



    Go into the installers programing (password 5309) and check the outdoor warm weather shut-down value.

    The OA Shutdown is set at the default 80°

  • pedmec
    pedmec Member Posts: 713
    You need to measure with wires disconnected from board so your not reading through the board.
  • akaDigger
    akaDigger Member Posts: 23
    pedmec said:

    You need to measure with wires disconnected from board so your not reading through the board.

    This is what I have been doing all along. I only took the reading hooked up because it was recommended by @HomerJSmith
  • pedmec
    pedmec Member Posts: 713
    I don't think he meant with them connected to the boiler. He meant to measure from the boiler thru the loop. That means you need to measure the resistance of the wires and the sensor. If you had a bad wire, spliced joint or anything to increase the resistance that would be interpreted as a different temperature than what it actually is.
    akaDiggerMikeAmann
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,983
    edited October 2022
    You could use one of these to check the control.
    Dial in the ohms you want based on a temp you want to see, and see if the control is reading the right temperature.

    https://m.media-amazon.com/images/I/81rH2w2U2iL._SX522_.jpg

    steve
    MikeAmann
  • akaDigger
    akaDigger Member Posts: 23
    edited October 2022
    Control module, 4-5 weeks. New boiler, 7 weeks.

    I began moving set points to compensate for the bad OA interpretation. I got the boiler heating and modulating. Baby steps. I've more tinkering to do. It likely works more efficiently than a default single set temperature. I hate it that I lose my efficiency just as energy prices soar.

    On the displayed OA reading, only an eight degree spread last 24 hrs. 62° down to 54° overnight. In reality, it dropped to 38°.

    On the upside, cycling at SET POINT MET is redistributing the passive heat from the sun on the kitchen tile.
  • MikeAmann
    MikeAmann Member Posts: 683
    Fourteen year old sensor. I suspect that whatever was used to weatherproof the actual sensor has begun to break down and moisture (condensation) is getting in. DO drop the sensor in water and take a resistance reading.