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I have some Marco 792775 gas logs, from the mid to late 90s. They haven't been used in 20 years. I don't have the manual, and I haven't been able to find it online. Seems the company went out of business a while ago.

They have a control knob that's different than what I'm used to for most gas logs... it looks like this:

Control knob for marco gas logs

I've had no trouble getting the pilot going. Turn the knob to pilot, press it in, gas starts flowing, hit the piezo-electric button, and boom, flame. If I keep it in for a while, the thermocouple heats up and the pilot stays lit. Great.

Turning the knob to off cuts the gas to the pilot, and it goes out 20-30 seconds later, as expected.

What I'm struggling with is actually getting the logs to fully light. Just once, I was able to turn the knob counter-clockwise past the pilot position (I think I depressed it, but I'm not 100% sure) and over towards LO and HI. The logs lit. However, every time since then, when I try to do this, the knob won't turn past pilot. I've tried turning with the knob depressed, turning with it not depressed, starting at the off position, starting at the pilot position, turning clockwise just in case, etc. Nothing seems to allow the knob to turn over to the actual running positions.

My theories are 1) the knob is broken, 2) there's some sort of safety mechanism that has engaged and won't let me turn the knob, or 3) I'm making some silly, embarrassing mistake.

Can anybody speak to these theories? Does anybody have experience with Marco logs and know how the knob is supposed to work?

  • Are you trying shortly after you lit the pilot? Try waiting longer. (Think: what would be the mechanism by which the knob would know the pilot is safely lit? Have to be thermal, eh? Temperature propagates slowly...) – Harper Oct 22 '18 at 16:17
  • Thanks... yes, I've tried waiting a while and coming back to it, with no luck, unfortunately. Also, there only appears to be one thermocouple in the pilot flame, and I know it's working because the pilot stays lit. – John Chrysostom Oct 22 '18 at 17:16
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Turns out, it was some sort of safety mechanism (though I'm not sure what it was for). I turned the logs back to off, waited for the pilot to go out, then kept waiting. After a minute or so, there was an audible metallic click/clang, like some sort of spring-loaded mechanism disengaged. I then was able to re-light the pilot, and turn the gas logs on with no trouble.

So, for anybody coming in the future, the procedure for lighting/using this type of gas log unit appears to be:

  1. Turn the knob to "pilot"
  2. Depress the knob, and hit the starter button until the pilot lights
  3. Keep the knob depressed for 30-60 seconds so the pilot can heat the thermocouple
  4. Release the knob
  5. Turn the knob counter-clockwise (without depressing) towards LO, then HI. If the knob won't turn, turn the knob to off, wait 10 minutes, and try again.
  6. To turn the logs off, turn the knob clockwise (without depressing) towards LO, then pilot. You don't actually need to get close to the pilot setting - about halfway between LO and pilot will be sufficient to turn the main part of the logs off, while keeping the pilot lit.

Hope this helps somebody in the future.

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