Direct Vent Gas Fireplace - Problems

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OldSalt

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Not sure if this forum handles these animals. Propane fireplaces seem to fit into a niche between plumbing, HVAC, and fireplace specialty stores.

I have a Direct Vent Propane Gas Fireplace, with a problem. See picture below:

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  • Unit is a Vermont Castings (formerly Majestic) MLDV500PSC
  • Unit has a "millivolt" Signature Command System electric ignition gas valve, with either a standing or intermittent pilot.
  • The unit lights and operates correctly.
  • Problem: All the little vents in the gas manifold won't automatically light. The flames stop distributing along the track from the back of the fireplace to the front. They stop at when they reach the front, without spreading to both sides (see yellow highlights, for unlit vents). The yellow circle highlights a horizontal slot, which should be lit and burning almost as high as those flames in back. The flames typically do not even spread as far as the pictures shows. There's a substantial amount of propane going up and out the flu.
  • I can manually light the vents with a lighter, so propane is being emitted from all the holes. I also checked each hole to ensure that there are no blockages, as much as I can check it without opening up the manifold. The manifold itself appears to simply be welded metal "box" with holes above, and a void below/inside, with a gas line attached in the rear connecting to the appliance valve. There don't appear to be any kind of tubes or Venturi inside the manifold for the gas to travel along.
  • I'm not sure whether or not this problem has existed since I first installed the unit in 2017. I seem to remember testing it and seeing all the vents light up. However, for the past several years, I've noticed that only the back of the fireplace was lit. This fireplace kit comes with rock wool "embers", which you use to break up into little bits, and spread around the vents, to provide simulated glowing embers. I expected that I probably botched the job, and blocked the ports with the rock wool. However, I just pulled it apart this year while I was finishing the fireplace surround, cleaned it out, and discovered the problem exists, even with all the rock wool removed.
  • Propane pressure specs for this unit require 11 to 14 inches of water pressure at the intake valve (from the house supply line), and 10 to 10.5 inches on the output side of the valve. I measured it, and found it to be about 10 inches in the intake side. I then checked pressure at the house regulator which was set between 10.5 and 11 inches, i.e. about standard. I adjusted the regulator pressure upward to 12 inches, retested, and got the same pressure at the valve intake. I then tested the output side of the fireplace appliance's valve with the fireplace burning. It recorded a pressure of 10 inches, i.e. within spec. However, there the fireplace lighting problem was unresolved.
I'm pretty much at a loss on how to debug this issue. If the problem isn't propane pressure level, it isn't the valve, then the only thing left is a blockage somewhere between the fireplace appliance valve, the tube to the manifold, and the manifold itself. Next step would be to pull the unit apart. The floor of the fireplace includes a sealed, about 1.5' to 2' rectangular plate. The manifold is mounted above that plate, the controls and gas line, below it. I'm not even sure what I'm looking for, other than to check the aluminum gas line between valve and manifold, and the manifold itself for blockages.

I can't even find anything on the web describing this kind of problem. I have no certain idea on how to proceed.
 
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WorthFlorida

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I know nothing about this type of fireplace though I did install gas log lighters on two fireplaces that I installed myself. I'm not sure if all of the pilot flames should be the same height. Seeing some with a white tip and others all blue flame tells me that the air and amount of fuel are not equal. As with most gas appliances, is there an air mixture adjustment? If there is check for any spider webs or debris. It doesn't take much cause problems. It looks like the base can be removed. I see slots on the sides where you can get a hand under them to lift it out.

This could be related and I learned it doesn't take much debris to hinder a gas flame. When I maintained a church, it was a brand new building with a commercial grade kitchen. There was a 6 burner natural gas stove by SATURN with six standing pilot lights. After a few months and little use I would find a few pilots out were out and the smell of gas was in the air. Relightning them with a flame they were OK for a few hours then out again. What I had to do was remove all of the pilot light gas copper tubes (about 1/8" tubing) at the gas manifold at the front of the stove. Then with compressed air I the blew air into the tubes. At every pilot nozzle a cloud of iron rust shot out. I was like a power. After that I never has a problem for more than six years when I retired.

If you have a compressor blow air into the manifold preferably from the backside forward. Use this type of rasper file in each pilot hole just to loosen any surface rust or debris. Do not remove metal. You do not want to make the holes larger. https://www.homedepot.com/p/Lincoln...th-12-Stainless-Steel-Reamers-KH575/100341101
 

OldSalt

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If you have a compressor blow air into the manifold preferably from the backside forward. Use this type of rasper file in each pilot hole just to loosen any surface rust or debris. Do not remove metal. You do not want to make the holes larger. https://www.homedepot.com/p/Lincoln...th-12-Stainless-Steel-Reamers-KH575/100341101

Thanks for the quick response. Whenever I'm lost on a project, I like to post my problems on the internet to find other lost people, and see if maybe they managed to find their way home, so I can copy them.

That's about the direction I'm heading. I already used a drill bit to ream out the holes, which seemed to work well enough. No rust or debris at all that I could see. Pulling this apart will be a chore, and I might have to find (or create) a replacement gasket, but that's what I'm going to do next. I can see the gas valve and supply tube below the fire floor, and the pilot assembly above it(see below), but not where the gas tube connects to the back of the manifold. Will pull that all apart and post what I find, plus pix if relevant. Blowing it out with my air compressor hose can't hurt (famous last words). I tried earlier to blow out the holes from the top of the manifold, but of course, that would just push whatever debris might be in the manifold further back in the tube.

index.php


In for a nickel, in for a dollar. It's disassembly time.
 

Fitter30

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Burner is dirty burner and or gas pressure isn't correct. Lp 11" nat 3 .5 . Take a strand of wire and ream each hole. If you use a air compressor pull the gas valve their not made for all the pressure.
 
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OldSalt

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Burner is dirty burner and or gas pressure isn't correct. Lp 11" nat 3 .5 . Take a strand of wire and ream each hole. If you use a air compressor pull the gas valve their not made for all the pressure.
Thanks.

Burner looks clean inside from what I can see from the hole, where the Venturi connects to the bottom of the burner. I already cleaned out every hole. I blew out the burner and Venturi detached from the valve. I also removed, cleaned, and inspected the Venturi orifice. I expected to find something, anything to account for the issues.

Next, I'm going to remove the bottom of the firebox and pull the supply tube from the valve to the venturi, and clean that out with a pipecleaner, then blow it out for good measure. I've been putting that off, because I really don't know what kind of RTV they used to seal that tube and the gasket around the hatch to the floor of the firebox. It looks like normal RTV. I've found some 800F stuff, but would prefer to find something for "standard" fireplace temps (2000F). I doubt it gets that hot at the bottom of the firebox, since it's right over the top of electrical wiring, the valve, and so forth, and non-insulated. I'll go through the Venturi with the pipe cleaner too, for good measure.

After that, I'm absolutely out of ideas. Propane pressure is within spec, before/after valve, valve works, everything's clear to the burner, and the burner is nothing but a pipe connected to a double shelled manifold, with holes in the top for the gas to emit. No tubes or anything inside the burner manifold to get blocked, as far as I can see. And as I've said, I can light every port, there's gas coming from every burner port, but the flame just quits communicating along the way. I can light any port, to get it past the port that won't fire, but I literally have to light every, single, needle sized port.
 

OldSalt

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Is there a air adjustment shutter on the burner? Did you happen to notice if their was a number stamped on the orfice?

Yes, on the Venturi. It's about 5/8" wide, i.e. wide open (on two sides of the pipe), set open for propane. I read somewhere that the standard is supposed to be 1/2", so I closed it a touch, but it made no noticeable difference.

I'll be away for a week, and will tear this down again when I return. I'll clean all tubes and the Venturi the valve to the burner manifold with pipecleaners, and then try again. Will look at that orifice and try to get your an answer on that, at that time.

Thanks.
 

WorthFlorida

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Have your tried using the log set after all this cleaning? It seems the only way for the flame to travel is across the top plate. The log set may hold the gas in place and allow it to travel to a lighted pilot to ignite and so on.

My WEBER grill the only ignitor is on the left burner. That left burner flames up before the middle and the right burner is fired up. The flame travels down a burner at the rear allowing it light the middle and right burner. That what you have as the row of pilots light up from the back to the front. The areas not lit up are several inches away from the nearest flame. The log may hold the gas in the area allowing time for the gas to travel toward the flame. For chuckles, with aluminum foil make a tunnel shape piece long enough to be over a flame and an unlit pilot. I'm sure the others will light.
 
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