# Marco Direct Vent Fireplace Pilot Light Problem



## xiii13 (Dec 21, 2009)

Marco Direct Vent Fireplace Model 794153B - 10 Years Old

Lately the pilot light is not engulfing the thermopile like it used to and when I turn on the wall switch to start the fireplace it will not turn on about 40% of the time.  I have thoroughly cleaned the entire head assembly of all rust and soot (thermopile, thermocouple, igniter, etc.) to no avail. I am taking an educated guess and am thinking it is because the pilot flame is weak and is not touching the thermopile.  I never received an owners manual for this fireplace (came with the house)and cannot find one online. There are several screws on the "gas valve/igniter assembly" for adjustments, but I do not know which one is used to adjust the pilot light.   Any help would be appreciated. I can post a picture of the gas valve if that helps to show which valve adjusts the pilot light.


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## DAKSY (Dec 21, 2009)

Generally, the pilot screw on a gas valve will be clearly labelled.
Some (Robert Shaw) will have a cover screw that has to be removed 
before the adjustment can be made, while others (SIT) have an exposed screw head.
Post a pic & we can possibly help you out...


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## xiii13 (Dec 21, 2009)

There are no markings on any of the screws.  Here is a picture:


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## DAKSY (Dec 21, 2009)

I believe the pilot adjustment screw is under the silver-colored
combination head (slotted/Philips) screw at the lower right on the valve,
below the ignitor. Back that screw out & there's probably a slotted screw
underneath it. To accurately adjust the pilot, you'll need a multimeter set to Mv 
& taking the readings from the TP & the TP-TH terminals...
You'll hafta turn the screw one way or the other & see which way turns the pilot up...
Generally, we try to keep the pilot at 550 - 575 Mv...
That number may or may not be attainable...
You'll be able to see what's happening with the TP under a steady pilot, anyway,
to determine if it's on it's way out...
If the Mv hold steady it should be OK...
If they're dropping, probably needs a replacement...
HTH...


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## xiii13 (Dec 21, 2009)

Thanks DAKSY for all your help - I will try this later tonight, when I can get a hold of a tester.  While I was searching for a board who might help me, my wife had a furnace repair guy come in and look at the fireplace and he was messing around with the silver single slotted screw just above the word "OFF", and made the pilot weaker.  He swears he put it back to its original position, but I'm skeptical.  He wasn't using any test equipment to test for MV when he was trying to adjust it.  Do you know what he was messing with or what this screw adjusts?


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## DAKSY (Dec 21, 2009)

xiii13 said:
			
		

> Thanks DAKSY for all your help - I will try this later tonight, when I can get a hold of a tester.  While I was searching for a board who might help me, my wife had a furnace repair guy come in and look at the fireplace and he was messing around with the silver single slotted screw just above the word "OFF", and made the pilot weaker.  He swears he put it back to its original position, but I'm skeptical.  I don't think he was using any test equipment to test for MV when he was trying to adjust it.  Do you know what he was messing with or what this screw adjusts?



That 's the pressure port to check the incoming gas pressure.
A tech can back the screw out & attach a manometer to determine if
the line pressure coming into your house is high enuff...
The screw at the far left is the pressure port be to check the pressure
going THRU the valve & into the burner, AFTER the regulator head.
Neither one of them should have anything to do with the pilot 
flame...


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## xiii13 (Dec 21, 2009)

So he didn't mess anything up by playing with that screw?



> Generally, we try to keep the pilot at 550 - 575 Mv…
> That number may or may not be attainable…
> You’ll be able to see what’s happening with the TP under a steady pilot, anyway,
> to determine if it’s on it’s way out…
> ...



"Probably needs replacement"  are you talking about the Thermopile or the pilot assembly?

Again - thanks for all your help


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## DAKSY (Dec 22, 2009)

xiii13 said:
			
		

> So he didn't mess anything up by playing with that screw?
> 
> Nope.
> 
> If they’re dropping, probably needs a replacement…



"Probably needs replacement"  are you talking about the Thermopile or the pilot assembly?

T-Pile


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## jtp10181 (Dec 22, 2009)

From the original post it does not sound like you actually took the pilot apart and cleaned it out, just the surface? If its a R/S pilot I would take the supply line out of the bottom and the orifice and clean all the crud out of the there. It looks like you might have a SIT valve though, so if you have what I like to call the "space ship" pilot, then you take the retainer clip off and pull the head off. Then you use an alan wrench to get the orifice out. Again, clean out everything in there.

If none of this works, it might just be time for a new pilot assembly. Often times we just replace the whole thing since both the thermopile and thermocouple seems to last similar lengths of time, and the rest of it just gets full of crud.


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## DAKSY (Dec 22, 2009)

From the posted pic, I'd say that's a Honeywell Valve,
& I'll admit that I haven't seen too many of em on newer products.
Some of the VC gas units have em, but we don't see many
of those either.
I do agree to pull the pilot spud (orifice) if there's minimal adjustment from the
screw. It doesn't take a very big piece of "crud" to block the hole.
Clean the spud & also depress the pilot knob & use the gas flow to eject 
anything from the pilot tube...


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