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Thermocouples

Dave_23
Dave_23 Member Posts: 190
Thermocouples

Hi  there.  I have a WM EG-35 steam boiler, standing pilot.  Over the

weekend I replaced my second 30 millivolt thermocouple in two years. 

The boiler was installed in 2001, and the stock WM-supplied thermocouple

which came with the boiler lasted  about 9 years.  Subsequently, I replaced

it with a Universal Honeywell Thermocouple (sorry, Honeywell...),

purchased for about $10 at the local hardware store, which lasted about

12 months.  I replaced it again over the weekend with my backup spare

(another HW Universal).  Any suggestions for makes and models of heavy

duty 30 mV thermocouples that may last few more years or that won't burn

out as quickly?  Note 1: WM no longer supplies their original

t'couples.  Note 2:  The form factor of the WM t'couple mount is

screw-in, same as the HW universal.  Any suggestions will be much

appreciated.  Dave.

















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Comments

  • Dave_23
    Dave_23 Member Posts: 190
    Thermocouple adjustment

    After discussing the matter of premature thermocouple failure with WM,

    Honeywell and Johnson Controls, the following has been suggested:  The

    premature failure I'm experiencing may be caused by overheating the

    thermocouple.  The techs I spoke with indicated that the thermocouple

    probe may be protruding too far into the pilot flame, causing

    overheating.  Question:  How far should a standing pilot thermocouple protrude into the flame?  Just barely, 1/8 inch, 1/2 inch, as much as possible, etc?  The tech from JC seemed to think "just the tip."  Thoughts and suggestions?
  • Slimpickins
    Slimpickins Member Posts: 326
    thermocouple stuff

    Just type in,  Thermocouple Testing Procedure in the search site area and you'll find everything you'll need to know. Tim McElwain, the host of this sub category, wrote the piece of info. You came to the right place.

  • Tim McElwain
    Tim McElwain Member Posts: 4,518
    Dave,

    If you have any problem finding the procedure let me know. The thermocouple you need is a Johnson/BASO K16LRA-36 which is a high temperature corrosion resistant thermocouple.



    The thermocouple should be 1/2' to 3/8" into the flame and the flame should be a soft blue flame not roaring or lifting and the tip of the thermocouple should be dull red not "cherry" red.
  • Dave_23
    Dave_23 Member Posts: 190
    Thermocouple adjustment

    Thanks for the info!  Now, I just have to find a distributor in our area for the Johnson/Baso item.  A Google search returns no useful info...
  • Tim McElwain
    Tim McElwain Member Posts: 4,518
    What is your

    location?
  • Dave_23
    Dave_23 Member Posts: 190
    Thermocouple adjustment

    Detroit,  MI  48201.  Anywhere within 10-15 miles is ok.
  • Dave_23
    Dave_23 Member Posts: 190
    Thermocouple adjustment

    Found a place - Young Supply, near my office.   I'll be ordering the K16RA-36.  No one could supply or identify the "L" in the reference to K16LRA-36.  Thanks for the assistance!  Dave
  • Tim McElwain
    Tim McElwain Member Posts: 4,518
    Sorry the K16RA

    is correct I do not know how I typed the "L" in there. Well after all I am 70 years old! Just a senior moment.
  • Dave_23
    Dave_23 Member Posts: 190
    Thermocouple adjustment

    No problem.  The K16RA looks like just the ticket.  Had I been on vacation during my recent pilot light outage/thermocouple failure, I'd have had a real mess on my hands, with outdoor temps below freezing.



    It never occurred to me that a thermocouple could fail so quickly.  From now on, I guess I'll have to have the neighbors check the indoor temp as well as collect mail and papers.
  • Tim McElwain
    Tim McElwain Member Posts: 4,518
    The truth is a

    thermocouple should last 8 to 10 years.



    So now that we have a durable thermocouple on the way you need to have a professional do a combustion test on your equipment. The failure of the thermocouples is a warning on a combustion issue which now needs to be addressed.
  • Dave_23
    Dave_23 Member Posts: 190
    Thermocouple adjustment

    What is the exact procedure for conducting a combustion test and what data will be collected and reported?  I will attempt to do this myself, however, I'd like some detailed info so I can interview and select a qualified boiler professional or company.  Thanks, Dave.
  • Dave_23
    Dave_23 Member Posts: 190
    Thermocouple adjustment

    I meant to say "I will NOT attempt to do this myself."  Sorry for the confusion...Dave
  • Tim McElwain
    Tim McElwain Member Posts: 4,518
    The reason for the

    combustion test is to determine if the system if firing correctly. The fact that thermocouples are being burned up tells me something is wrong. If you have gone through my Thermocouple Test Procedure that is available here then the next step is combustion testing.



    The test will measure CO2, O2, Flue Gas Temperature, draft, and CO (Carbon Monoxide). A good combustion analyzer (Electronic) will be able to determine these parameters. Then the technician can determine from there a number of things.



    There are many things that can affect operation of your system such as:

    1. Not enough air for combustion

    2. Incorrect venting

    3. Undersized gas piping

    4. Airborne contaminants, laundry room nearby, dryer operation

    5. Over or under fired boiler

    and many more, a professional combustion/gas technician will be able to determine any problems which need to be corrected.
  • Dave_23
    Dave_23 Member Posts: 190
    Thermocouple adjustment

    Tim,

    The Johnson Controls K16RA works great.  I could tell right away it's heavier duty and more substantial than the Honeywell Universals.  One issue that I did have to resolve (with a little ingenuity) was figuring out how to adjust the installed height of the K16 relative to the pilot flame.  When installed as supplied into the stock WM pilot/TC mount, the K16 protruded a about 1/4 inch too far up into the flame. (Note: The Honeywell Universal did the same).  What I did was install a thin hardended steel metal spacer ring over the TC "shoulder"  to hold it off a bit from the flame to ensure proper positioning.  Only thing I can conclude is that the stock WM TC must have been shorter in length or had a different form factor.  Rest assured that the K16 TC is securely installed and is not  "jury rigged."  I believe my solution was reasonable, given the situation.  Result:  Secure mount, proper orientation of TC in the pilot flame; dull, dark orange glow from the tip to about a 1/2 inch down.  Thanks again for your assistance.

    -Dave
  • Tim McElwain
    Tim McElwain Member Posts: 4,518
    Dave that is great

    be sure and follow my advice and have professional take a look at the unit to perhaps fine tune it to eliminate other issues
This discussion has been closed.