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  1. #1
    Join Date
    Dec 2010
    Posts
    28

    Gas pressure too low, replace the gas controller?

    I recently had my Lennox MDP-4035CPM (propane) cleaned by a professional and the guy checked the incoming gas pressure. He said it was low, about 10 psi when it should have been 12 psi. He thought this might have been the issue with it causing soot. He also thinks I should replace the gas valve (about ~$2) and another 1-2 hrs labor, about $4 total. This after a cleaning bill of almost $5.

    My questions are
    • Do you agree that a low gas pressure could cause the soot problem? (It seems to me that it would have nothing to do with the viability of the flame, rather it would govern how high the flame was in the firebox).
      Do you agree that a gas valve that runs a little low is a danger and should be replaced?


    Thanks,

    Bob
    Last edited by Chris_Worthington; 09-19-2013 at 10:31 AM. Reason: Pricing Removed

  2. #2
    Join Date
    Aug 2013
    Location
    OKLAHOMA
    Posts
    143
    What was the out going pressure ?

  3. #3
    Join Date
    Feb 2010
    Location
    Calgary, Alberta
    Posts
    1,156
    Most propane valves can run down at 10", like was mentioned above, the outgoing pressure is what matters.
    There could be issues with the vent as well.
    The regulator outside the house is what controls incoming gas pressure, so I can't see how changing the appliance gas valve will help....

    Time for a second opinion I think.

  4. #4
    Join Date
    Dec 2010
    Posts
    28
    Sorry for the confusion. Yes, that was the "going out" pressure. I called second level technical support at Lennox and they said that 8 in was way too low and will definitely cause excessive soot. They recommended changing the gas valve. Even though the unit has a "20-yr Warranty" they exclude controllers so I am out of luck.

  5. #5
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,305
    Whoa! You're all over the place. Gas pressures at the appliance are stated in terms of inches of water column or wci. The typical inlet pressures for LPG under full load meaning this appliance on 'hi' plus any other attached appliances firing on 'hi' ranges from 11-14wci, which equals 1/2psi. On an LP system, you should have a second stage regulator which reduces pressure from the tank at about 10 psi down to this 11-14wci. If your inlet pressure is too low, have a qualified technician increase the pressure at the regulator or consider larger diameter piping for long runs. Once you can reliably deliver this amt. of gas under full load to all appliances, then you can look at the gas combination valve attached to the appliance. There is a way for a pro to test the line pressure directly then correlate it to the inlet pressure once it has entered this valve. Unless a valve gets damaged such as by line voltage, it usually does not need to be replaced. again, there are ways for a pro to test the valve that cannot be discussed here as it would constitute DIY advice. Yes, low inlet pressure and low manifold pressure can result in sooting and carbon monoxide formation. You might need to shop around for a different Fp repair technician.

    FYI, no discussing pricing on this site.

  6. #6
    Join Date
    Dec 2011
    Location
    PA
    Posts
    206
    I second what hearthman said, I would highly recommend a new company(or specifically request the senior tech) to service your fireplace.

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