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Lennox Unit Heater Gas Valve Testing

arliss
arliss Member Posts: 3
edited December 23 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: 3
    edited December 23

  • ratio
    ratio Member Posts: 3,802

    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: 3
    edited 12:31AM

    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: 3,802

    Replace the valve.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,584

    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.

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