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Condensing Boilers and 2PSI Gas

Rankin Member Posts: 26
Can anyone tell me the proper regulator I'm supposed to be using for a Lochinvar Knight KBN-501? I've been asked to commission a boiler that isn't firing for a local contractor. I went in today to look at it and it appears the gas pressure drops about 7" (from 10" to 3") for a split second when the gas valve opens and will not fire. With some extreme adjusting, I was able to get it to ignite but not stay lit. I know for a fact we have lots of air, we definitely have good spark, so I'm convinced it's a gas issue.

I've tried using sizing applications from Maxitrol and Actaris without much success, and I left a voicemail with Lochinvar's tech support, but I'm guessing it's not considered an emergency on the weekend.


  • kcopp
    kcopp Member Posts: 3,820
    edited February 2011
    I am no expert....

    although I just did a pretty large 2 psi sysste, w/ 4- 200k  FHA furnaces, 1- 380k Noritz, and a bunch of commercial  kitchen stuff... I used a Maxitrol 325-7L on the tankless. I ran 3/4"  black to the regulator then 1" out to the tankless. It works fine. It was pointed out to me that you should have a fair amount of pipe down stream from where you come out of the regulator ....say 15'-20'. Is this NAT or LP?
  • icesailor
    icesailor Member Posts: 7,265
    edited February 2011
    Lochinvar Gas:

    Read the instruction manual. Although it has a 1/2" gas connection, does it say to run 3/4" full size from the meter? That's the first thing Tech Support may ask.

    Where I work, my wholesaler is selling a lot of Lochinvars. I hear a lot of installers having problems like this. They are all LP. I don't know what they are doing to fix them but they get fixed. There is a guy who really specializes in these ModCon boilers and they call him. I've heard about digital manometers but I don't know all.

    Just telling you they have "Issues". Solvable though.

    OBTW, These are all LP, FWIW
  • Rankin
    Rankin Member Posts: 26

    I have 3/4 to the reg and 1-1/4 after it. I'm 20 equivalent feet away with my reg. It is Natural and I'm using a digital manometer. I'll try their tech support this morning and hope for the best!

  • Brad White
    Brad White Member Posts: 2,393
    edited February 2011
    Suspect line pressure drop.

    That kind of sudden drop and restoration speaks of under-sized gas lines to me.

     Also is there a pressure regulator in the train? You did mention 2 psi then 10 inches. The drop and restoration condition in that case also says low gas line size, not enough buffer volume to maintain steady pressure, or the regulator response time is too slow, or both.

    EDIT- just saw that you posted, you do have a regulator. Sorry.

    2 psi? Here in MA at least, one cannot run over 14 inches (0.5 psi) inside a building without a special permit. Codes vary place to place, I know, so I was just curious about your area.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Reg issues...

    If the diaphragm vent for the up stream pressure regulator is plugged, the regulator will work sporadically.

    The distance issue between primary and secondary reg's becomes evident during the run process, and shows in the form of flame fluttering because the two diaphragms can "see" each other and sets up a counter harmonic between the two diaphragms, or so I was told :-)

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Rankin
    Rankin Member Posts: 26
    according to the code book I have..

    one and two family dwellings and row housing is max 2 PSI

    Commerical Buildings max 20 PSI

    There are permits required for high pressure gas (over 14") and the necessary permits are in place. This is a new commercial building. Knight will be used to provide hot water for four fan coils. I know from training on other boilers I have, we were told we must use certain regs for condensing boilers.

    PS: Tomas Kaberle in a Bruins jersey is a hard thing to watch.
  • Henry
    Henry Member Posts: 988
    Gas pressure

    We run 2, 5 and even 10 psi into apartment blocks for 2 to 4 Lochinvar condensing boilers. The gas pressure regulator are on each or on a headder only three or four feet away from the gas valve. BTW Always natural gas. We have not experienced any problem even with the 2 psi ventless regulators at less than that distance.

    We have had an experience with some similarities as yours on a rooftop make up system. The piping was correctly sized. The 10 psi to 14 inch regulator was three feet away. The gas pressure would drop every time. We checked the spring colour and it was fine.We finaly found that our supplier did not put in the proper orifice for the 2,000,000 BTU regulator.

  • Rankin
    Rankin Member Posts: 26
    Reg stuff

    Building reg is well over 100 ft away. The 2psi>"w.c. reg I have has an vent limiting orifice installed in it. I'm highly suspect of it, as all the other units in the building are running.

    Are there certain types of regs that are to be used with mod/con boilers?
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