Mendota DXV45 Delayed Ignition Problem

teddybaehr Posted By teddybaehr, Jan 26, 2016 at 10:01 AM

  1. teddybaehr

    teddybaehr
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    Jan 26, 2016
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    I'm new to the Forum, so let me start off by saying "hello" to everyone - this is a great source of advice and am happy to be here.

    My house was built in 2008 and I chose a Mendota DXV45 in my living room. It's been a so-so performer since new. I'm running propane and the fireplace was converted (supposedly) from NG when installed. I purchased the Mendota because of its heating ability and general excellent quality rating. I saw many video-commercials of Mendota fireplaces and the local store had display items that looked great. Mine has never achieved the look of a woodburning fire - it's always looked more like my gas range!

    But putting aside the look of the flame for a moment, it's also always been a slow starter. From Day 1 it's started with a "whooph". From the time the unit is turned "on" there's been a lag of 5-7 seconds and then boom, it ignites. When the fireplace was new I had the technicians out twice with no improvement; they said it's pretty normal for these fireplaces and wouldn't hurt anything. The technicians didn't seem too savvy, so I tried another company and paid another chunk of cash to have them clean and address the delayed ignition problem with no better a result. So I put up with it for years, but was always uncomfortable - the fireplace didn't get used much mostly because of the starting problem (my wife won't go near it). Last season the pilot wouldn't light. When I called the techs I was told they were swamped and it would be a month or two before they could schedule an appointment. I'd had enough... I generally don't mess with gas, but time for tools.

    It took me about 30 seconds to see the problem - the thermocouple was burned through. A little research revealed that a hi-temp thermocouple should have been installed when the unit was converted to LP... it wasn't. I had to remove everything to get the thermocouple out - a very tight fit. I was hardly impressed with Mendota's design; hard to get at things and a flimsy arrangement for the pilot assembly and unfriendly to maintenance. I elected to install a new pilot assembly since I found the flame hood on the pilot was bent and cracked (probably during a ham-fisted installation) and didn't want to have to do the job again if the thermopile needed replacement. I sealed everything up with hi-temp sealant, re-installed the logs per instructions, and fired it up.

    It worked as it did before... started a little faster, but still a lag and a "whoomph". This season when I started the fireplace I got a bit more than a whoomph, I got a fireball and what I would call an explosion. One thing about Mendotas - the glass can definitely take an overpressure!

    Here's my question - how can I get rid of this delayed start once and for all? It's definitely not normal and has been there since new. Here's what I can tell you:

    1. The pilot, thermocouple, and thermopile are clean, good clean flame (although it hits the thermopile at the base - I've read it should engulf the thermopile or hit it more towards the tip)
    2. The thermocouple is operating correctly - voltage is spot on; pilot is stable
    3. The thermopile puts out around 330mv which is above the 250mv requirement stated in the manual
    4. The logs are installed following the manual to the letter - everything matches the placement photos
    5. Nothing is blocking the pilot assembly

    At this point I'm wondering whether I've been fighting an uphill battle with this fireplace from the start, and whether it was installed, and converted to LP, correctly. I'm also wondering whether I have an issue with the gas valve, or whether the mixture is somehow wrong. I don't have any issue with sooting, but the unit has always produced a pretty meager flame compared the tall, licking flames you see on the videos.

    When you build a new house it can be frustrating dealing with system installers. I've had to sort out perplexing issues with improperly installed heat pumps, well pump, garage door openers, and a host of other items that required significant rework. Time now to fix this *&$#%(@# fireplace!

    I appreciate any advice you can provide - thanks in advance!!
     
  2. DAKSY

    DAKSY
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    Dec 2, 2008
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    I take it you still have the manual, since you've managed to find & replace the pilot assembly.
    You are correct in that the pilot flame should engulf the top 3/8" of the T-pile. The pilot being low on it may
    account for the low mV putput. It should be more in the 550 mV range with the burner off.
    There should be a pilot adjustment screw on the valve. You should be able to adjust the flame
    & read what you're getting with your multimeter. Try to bring the mV up.
    Your blue flames indicate a lean ATF ratio. That can be adjusted by tweaking the air shutter.
    It should be cited in the initial setup instructions in the manual, under "Air Shutter" or "Aeration."
    Try closing it in small incements, say 1/16" at a time until you get the flame presentation you want.
    The correct flames should be blue at the bottom & yellow at the top.
    Once you get orange tips with a little bit of black, you've gotten it too rich. Gradually back it off to yellow.
    The ATF mix may also be causing your delayed ignition.
    HTH.
     
  3. teddybaehr

    teddybaehr
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    Jan 26, 2016
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    Thanks Bob,

    Yep - I have the original manual and have been going by it.

    The pilot on this unit has never made much sense to me. It has a three-way hood - one pointed at the burner tube, one at the TC and the other at the TP. It's not adjustable. When I found the hood bent on the original pilot assembly it looked like someone put pliers on it to get it to point higher up on the TC and TP and probably get the flame closer to the burner. The hood is actually welded on and bending it caused a crack, so I replaced the whole assembly. But I can see what the tech was trying to do. If the hood sat a little higher the flames would cleanly hit the upper part of the TC and TP which would help kick up the voltage.

    I see the pilot adjustment screw and the air shutter damper. With the glass back on I'll try adjusting the air mix and report back with the millivolt readings.

    The fact this this unit has had delayed ignition problems makes me wonder if I'm missing something fundamental. I know the techs fiddled with everything and it was still a hard starter. They finally gave up and declared it normal!
     
  4. DAKSY

    DAKSY
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    I have a Heat & Glo 6000TRXI-IPI-LP had a delayed ignition when I replaced a cracked ceramic burner.
    I eliminated the problem by sizing the closest burner ports to the pilot & by drilling the same diameter
    into the burner even CLOSER to the pilot flame. That allowed the first burst of LP to ignite almost immediately.
    I'm not telling you to modify your burner, but it worked for me.
     
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  5. teddybaehr

    teddybaehr
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    Jan 26, 2016
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    Yeah, I noticed that you mentioned doing that in response to another fellow with a 'boom box'. What's really drove me nuts is an acquaintance with the exact same unit installed around the same time and also on propane. His ignites immediately, within a second of hitting start. I noticed his logs were laid out the same way, but the coals, vermiculite, and inswool were set up differently. I never thought it made any difference, but maybe that's plain wrong. I went back and found three different manuals from Mendota on the DXV45; all three have different instructions on how to set up this material during the lay-up. I believe the 3 versions of the manual represent different variations of the DVX45, but it's interesting that they keep changing this step.
     
  6. DAKSY

    DAKSY
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    You DEFINITELY don't want ANY ember material near the pilot.
    That can help in the delaying the ignition,
    by diverting the burner LP away from the pilot flame.
     
  7. teddybaehr

    teddybaehr
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    Jan 26, 2016
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    Okay - I performed everything suggested - attached a few pictures to show what's going on. I tweaked the pilot jet, adjusted the damper, cleaned the thermopile (it was pretty clean already), and fired up the pilot. I registering around 800 mv with the unit off, double what I measured before. You were right on the money.

    The second picture shows the flame output from the pilot - this is with the door off (so I could get a clear shot), with the door on the flame has more yellow in it. I removed the logs to show that the flame clearly envelopes the lower burner tube. As you can see in the third picture, this unit has two burner tubes; the rear unit is engaged separately from the front burner if you desire more heat.

    Before I try to fire the main burners... a question. Can I try to fire it without the logs - just the tubes alone installed? The reason I ask is some stuff I've read suggest the logs are required in order to properly flow the gas for quick ignition. I can't understand why this would be true since the gas should flow quickly to the short tube adjacent to the pilot and get things going. I'd like to eliminate all potential reasons for delayed ignition by starting as simple as I can and testing in steps - it seems to make sense to first try with bare burners and establish if it ignites quickly. If it doesn't, then it would seem to me that something is fundamentally wrong.

    IMG_2447.JPG IMG_2454.JPG
    IMG_2455.JPG
     
  8. DAKSY

    DAKSY
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    815 mV will absolutely SMOKE the T-P & the T-C. Turn it down to about 550mV.
    You CAN safely light the unit without the logset installed.
     
  9. barmstrong2

    barmstrong2
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    I would want to know the manifold gas pressure after the gas valve. For propane, it should be 10" WC. If the technician missed a step in the conversion, it would be low, around 3.5" WC. This could cause poor flame picture and delayed ignition.

    What daksy said about drilling a couple extra holes closer to the pilot flame sounds extreme, but, I have done this also. Gas appliances are manufactured for use with natural gas and don't always translate to propane. The big difference is the natural properties of the two. Natural gas is lighter than air and will float up. Propane is heavier than air and sinks. Many times, the burner/pilot design works well natural, but, with propane being heavier, it drops away from the pilot flame, thus needing to build until... Boom! Any more than 3 seconds is unacceptable, for my liking.
    Regarding doing this, with a new unit, I have contacted the manufacturer tech support and obtained authorization to do so, so as not to void warranty. With an older unit that's not a concern, but, just to add some credibility to what we're telling you.
     
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  10. teddybaehr

    teddybaehr
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    Jan 26, 2016
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    Thanks to you both for your advice. I'll do some more tuning and try to get the mv reading where it's supposed to be. On this unit I've noticed that the difference between a clean and dirty TP is almost a factor of 2. The TP never gets that dirty, but even when it looks clean if I wipe it down and give it a quick cleaning with crocus cloth or fine steel wool the readings shoot up. Annual maintenance is clearly needed in this department.

    The pilot flame completely engulfs 3 or 4 holes of the burner tube segment adjacent to the pilot - any gas getting there is going to ignite immediately. The area around the pilot has always been clear, so that's not an issue. Since the rear burner tube is never receiving gas during start-up, the build-up of propane that ignites with a boom must be coming from the bottom main burner tube. It's hard to see in the picture I posted, but the segment of the burner tube running to the pilot is angled up... so propane has to run up hill a bit to get to the pilot. This has always troubled me since, as you point out, LP is heavier than air. If indeed the manifold pressure is low, the flow of propane into the burner tube might be slower that it should be without enough pressure to "push" it up the segment of the tube to the pilot. That would explain the persistent delayed ignition and the meager flame I've been experiencing. Great catch on that important point about checking manifold pressure - I feel dumb for not thinking of that!

    I've long felt that my woes with this fireplace started with a bad installer; it wouldn't surprise me one bit that he missed this important step. I have a lot of LP appliances in my house: 2 fireplaces, furnace, range, generator, and garage heater supplied from an underground 500 gallon tank. All the other units work flawlessly. I don't have the tools needed to check the manifold pressure, so I'll locate someone who can.
     
  11. DAKSY

    DAKSY
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    One other thing to take a look at while you have it apart is the alignment
    between the burner orifice & the primary burner. If your burner points UP
    & the burner orifice is nearly horizontal, there's your issue.
    They BOTH need to be pointed in the same direction.
     
  12. barmstrong2

    barmstrong2
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    Do you have rock wool, burning ember material, to place over the burner ports? I always put that ember material across the burner ports, mostly to improve the flame picture, but, it would also create just enough of a restriction to maybe push the flow of gas up the lighter tube a bit quicker. There ember material should be dime size pieces, in shape and thickness. They lay loosely over the burner ports.
     
  13. teddybaehr

    teddybaehr
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    I wish I had uploaded a clearer picture... the main orifice delivers to the front burner tube which is a downhill run, so that's good. However, the branch off the front burner tube running to the pilot is back uphill, a pretty good angle too. That might be great for NG, but might be an issue with LP. The rear burner tube runs downhill from it's orifice and then sharply uphill along the 'c' bend. The pilot flame catches the rear tube nicely and the rear burner has always ignited immediately with the flame running around the tube quickly from the pilot outward.

    I think barmstrong2 is on to something with the manifold pressure. If the pressure is low the LP could be filling the main burner tube and pooling but taking its sweet time to wander up to the pilot - the result is a late ignition and boom. I did try firing it up with the unit with bare tubes... marginally better, but still a delayed ignition - 6-8 seconds and a strong boom. So I doubt loading logs, vermiculite, rocks, and inswool is going to improve things. I did tune down the pilot flame, but I can't get the TP voltage below 620 mv.

    The inswool was never installed over the burner tube port holes, but laid adjacent to them. I tried once placing inswool over the ports with exactly that thought in mind, but it didn't seem to help. And one good 'boom' sent the inswool flying!

    I suspect that the LP conversion on these units has to be done with precision. If properly done everything's all set; but if errors are made you wind up walking down the road I've been on. I'm waiting to get help testing the manifold pressure - I'm betting it'll wind up being low. It explains both late ignition and a weak flame.

    Thanks for your continued help - it's very much appreciated!!
     
  14. BDScott

    BDScott
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    I could not have written thread any better than teddybaehr. This is precisely my experience with this model. My only difference is that I have drilled additional gas holes nearer the pilot for a faster ignition, but with no different results. I believe the angle of the main burn tube is a design flaw for use with PG. If accurate, it is a latent design defect for LP conversions. If true, it will always be defective. I was hoping this thread had a resolution. Did we ever learn how to get the 'WHUMMPP!' to stop? Any remedy?
     
  15. DAKSY

    DAKSY
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    Has the Burner orifice been removed & inspected? I'm wondering if it is correctly sized for LP gas.
    LP burner orifices have smaller holes due to the higher line pressure. If you still have an NG orifice,
    the larger diameter hole may be allowing the LP to disperse before getting to the pilot flame.
    The smaller hole in the LP orifice would tend to create higher pressure & a "jet" of gas shooting
    further into the burner tube...
     
  16. Millbilly

    Millbilly
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    I would take the burner out and inspect the burner orifice size, should have a number stamped on it and check for partial blockage. While you are at it inspect inside burner tube at the air shutter and make sure there is no soot or insects obstructing air flow. Then make sure installer replaced gas flow regulator tower to lpg one. It would be right on the valve and should be obviouus because the torque screws will likely not be safety heads and lack the factory indicating paint seals on screw heads, and check pressure.
     

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