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Lennox Unit Heater Gas Valve Testing

arliss
arliss Member Posts: 6
edited December 2024 in Gas Heating
valve2.jpg unit heater.jpg valve.jpg gas valve.jpg

I have a Lennox unit heater that is failing to light even with assistance with a torch

So far I have
checked the exhaust vent is clear of obstructions
removed and cleaned all of the venturi tubes
removed and cleaned gas manifold and nozzles
Last year replaced igniter and flame sensor
this year tested igniter and cleaned flame sensor
tested and I get 24 volts at gas valve when it is called and I hear an audible click in the valve

at this point the unit will barely ignite the first burner and I cannot light anymore than that
it is a 2 stage valve and I suspect the valve is the culprit

I have removed the valve and cleaned the the coil connections on the tiny circuit board
when I test the coils for ohms I get 44 ohms on the small coil and 17 ohms on the large coil my understanding is they should both be reading 40 to 80 ohms.

any input if this could be anything other than the valve at this point would be appreciated

Comments

  • arliss
    arliss Member Posts: 6
    edited December 2024
  • ratio
    ratio Member Posts: 3,988

    There is nothing inside the gas valve that can be repaired, replaced, cleaned, or otherwise fiddled with. If it's bad, replace it.

    What's the incoming gas pressure? It should be in the 7-14" range with the valve closed, and it shouldn't drop more than a half-inch, but even with several inches of drop it will still operate fine. If ti drops to less than 3-4 inches, that's the problem.

    What is the voltage on the gas valve terminals when the valve tries to open? Should be 24ish volts, less than 20 volts is an issue.

  • arliss
    arliss Member Posts: 6
    edited December 2024

    I have 28 volts at the meter and I hear the valve click when called but it seems like there is not enough gas to run it. I am wondering if because this is a step valve it is not fully opening.
    I do not have a manometer yet to check pressures.

    I cleaned the contacts where the mini board on the valve connects to the two solenoids they are just spring points of contact and the solenoids had very slight corrosion at those contacts

  • ratio
    ratio Member Posts: 3,988

    Replace the valve.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 17,797

    Check the install manual and you need a manometer or a low-pressure gauge to go any further. The inlet pressure should be about what @ratio mentioned. The outlet pressure is usually 3.5"wc. Check the manual.

    If you have power on the correct terminals on the valve and here it click and your inlet pressure is good and your outlet pressure is low it's probably the valve. Some valves you can adjust the outlet pressure some are sealed.

  • arliss
    arliss Member Posts: 6

    My Valve VR8305P4337 is apparently discontinued. Is there a cross reference site where I can match a suitable replacement.

    It is a step opening valve 3/4 x 3/4

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,477
    https://forum.heatinghelp.com/discussion/comment/1829135#Comment_1829135
    Screenshot 2024-12-24 at 11.44.41 PM.png

    I can clearly see that you have not followed the instructions above. I cna say that with confidence by looking at this photograph.

    Screenshot 2024-12-24 at 11.46.09 PM.png

    Your next step is to thro that valve in the scrap pile and get yourself a new valve. You also need to test the replacement valve with a manometer. and check the flame with combustion testing equipment. Do you have that stuff? Do you know how to use that stuff?

    If you try to use that valve we will be hearing about you in the evening news broadcast?

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,477

    https://customer.resideo.com/en-US/Pages/Product.aspx?cat=HonECC%2520Catalog&pid=VR8305P2224/U&category=VR8305&catpath=1.2.7.16.9.8&rank=5&v1=Sort.1.Product.Rank&asc=1

    This should work

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • 109A_5
    109A_5 Member Posts: 2,410

    Hello arliss,

    The datasheet on that VR8305P4337 gas valve. All 16 pages.

    https://customer.resideo.com/resources/Techlit/TechLitDocuments/68-0000s/68-0109.pdf

    The outcome will probably be the same. From the manual.

    image.png
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • HVACNUT
    HVACNUT Member Posts: 6,769

    I would try the torch again. Much easier than disassembling the gas valve. MERRY CHRISTMAS!

  • arliss
    arliss Member Posts: 6
    https://forum.heatinghelp.com/discussion/comment/1829406#Comment_1829406

    Thank you this Looks good except mine is 3/4 in and 3/4 out and this is 1/2 x 1/2
    And I have not disassembled anything on the valve other than removing the plastic dust cover so I could test voltage on the coils.

  • pecmsg
    pecmsg Member Posts: 6,079

    that’s not how you test the voltage.

    EdTheHeaterMan
  • arliss
    arliss Member Posts: 6

    I understand that I need to test for 24 volts at the valve terminals . I have that .
    I did read somewhere that as this is a step opening valve each coil should be in the 40 to 80 ohms range when tested separately. I get 44 on one and 17 on the other that may not mean anything but that is the readings I am getting on them.

  • HVACNUT
    HVACNUT Member Posts: 6,769

    So did Santa bring you a manometer so you can verify there's 24 volts to the valve but zero manifold pressure?

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