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Main burner blowing pilot off.

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JStar
JStar Member Posts: 2,752
Bradford White 40 Gallon natural draft. Forget the model number. Has a newer Honeywell style gas module. Intermittent pilot outage. I notice that every time the main burner lights, it hits the tank, rolls back a bit, and pushes the pilot flame off of the thermopile, then it evens out and drafts into a cone through the flue. Thermopile reading dips from +450 to about 320mV when this happens. Tech support said they had never heard of this happening before.



Is this most likely a draft issue? I only did a quick smoke and mirror test, and checked out okay. I hate the word "okay", but I didn't have an accurate means of measuring draft at the time. This problem has been going on since last winter. Happens during all seasons, all times of day.

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  • lchmb
    lchmb Member Posts: 2,997
    edited October 2011
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    pressure test

    Is this natural gas or propane? Have you done flow and lockup to the unit? Manifold pressure's? Has the pilot orifice been cleaned? Burner? Is this the newer style that has the air drawn in the bottom and if so are the dust screens clean? I have not come across a thermopile on a water heater so that's new to me......

    Is this the newer model with the mechanical flue damper that is powered through the thermopile?
  • JStar
    JStar Member Posts: 2,752
    edited October 2011
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    RE

    Natural gas.

    City gas pressure = 8" WC

    Manifold = 4" WC



    Pilot and main burner tubing clean. Screens are clear. It uses a thermopile to generate voltage for a diagnostic LED.  There is no mechanical damper on this unit. There is just a roll-out safety on the combustion door.



    I don't know what "flow and lockup" is....
  • lchmb
    lchmb Member Posts: 2,997
    edited October 2011
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    I deal

    with propane so your better to post this in Tim's section under gas heating. I would check to make sure you have no obstructions in the baffle and have someone come in to verify flow and lock up..also, what did you use for a guage to verify pressures? Also, 450 is low for a thermopile, I am assuming this is under load. I generally like to see them over 500. Is the thermopile new and you said the tube is clean, but is the orifice?
  • Techman
    Techman Member Posts: 2,144
    edited October 2011
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    Pilot

    is the manifold press supposed to be 4.0"wc  or 3.5"wc. ? Is the pilot/thermopile  positioning to each other correct? Can you measure the pilot orifice w/  a "orifice drill bit index " set ? Is the pilot flame adjustable? Is pilot flame/main burner distance correct?
  • JStar
    JStar Member Posts: 2,752
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    RE

    This water heater does not allow any adjustment of the pilot or main burner.. And yes, it does require 4" WC. I repositioned the thermopile in the pilot flame and did not have any changes in mV readings. I did not check the orifice size.



    I ordered a new burner assembly and gas valve to be safe.
  • meplumber
    meplumber Member Posts: 678
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    450 is low for mV. I agree with Ichmb

    The gas valve needs around 550 for it to begin to work and that is if the gas valve is functioning properly.



    Pose this question to Tim.
  • lchmb
    lchmb Member Posts: 2,997
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    curious

    Is this the newer style water heater with the air intake from the bottom of the tank? If so, have you cleaned the screen to make sure it's not plugged with dust or other contaminates? 
  • JStar
    JStar Member Posts: 2,752
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    RE

    Tech support said they require a minimum of 350 millivolt. I asked if that number was under load, or just the pilot. Their response...."(long pause) Ummm, both...I think."



    I changed the thermopile placement and did not get any higher mV's. The heater would fire up a number of times, then fail either mid cycle, or during burner light off.



    The air screen is clean like brand new.
  • Tim McElwain
    Tim McElwain Member Posts: 4,628
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    That generator

    on that water heater should be putting out 750 millivolts open circuit. If tech services told you other wise they are wrong.



    Check the resources section above and look for Tims Closet for procedure for troubleshooting.
This discussion has been closed.