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Diagnosing low gas valve pressure on WM CGA-5-PIDN

fentonc
fentonc Member Posts: 273
in Gas Heating

My boiler uses a Honeywell VR8204A2001 gas-valve. I had clocked my boiler at the gas meter only drawing about 120k BTU/hr, even though it should nominally draw 140k BTU/hr. I had the boiler guy try increasing the pressure at the gas valve when he came out to service it, but it seems to top out at about 3" W.C. (vs the nominal 3.5" W.C. for the boiler). The gas pressure on the line is towards the lower end, but above the minimum spec as it measures at 5.5" W.C., and turning the adjustment on the gas valve let's us lower the pressure below 3", but when it's all the way open it doesn't go higher than 3". It otherwise operates as intended.

Any idea what could be wrong with the gas valve? It seems like the spring in it is replaceable (as that's part of switching between NG and propane), although I have no idea if that could be the culprit. Does the whole assembly just need to be replaced? I have no idea what the typical failure mode on a valve like this is.

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,157
    edited November 1

    The first question I would ask is "Does your home heat properly at design temperature? (Design temperature = coldest day of the year). If you can answer yes to that, and the boiler has no other operational problems, then it ain't broke… Don't try to fix it.

    OR, Are you trying to solve a problem? Then explain the problem you are trying to solve.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    SuperTech
  • fentonc
    fentonc Member Posts: 273

    The home heats fine at the design temp, as both the boiler and radiation are way bigger than necessary, but the combustion efficiency is like 76% instead of the nominal ~83% it should be because of the ~140% excess air. My motivation was to improve the combustion efficiency.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,157

    Most boilers are oversized and operate inefficiently as a result. If you have a 120,000 BTU input boiler and you do not have any operational problems then increasing to the rated 140,000 BTU will make the boiler more oversized. That may actually make you burn a little more fuel that the current setup.

    To get the boiler to the 140,000 rated input may require increasing the size of the pipe from the meter to the boiler. Or you may be able to go the the meter and increase the pressure at the regulator from 5.5 to 6 or 6.5. bre careful doing that because other appliances may over heat if they do not have an appliance regulator to compensate for the higher inlet pressure Clothes dryers, and cooking ovens sometimes do not have internal appliance regulators, so you would need to add some to get you boiler up to 140,000 (which is probably oversized and will increase your usage.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,157
    edited November 1
    https://forum.heatinghelp.com/discussion/comment/1817530#Comment_1817530

    What boiler do you have? Do the burners have air adjustments close to the orifice location? Is it the WM from past conversations?

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • fentonc
    fentonc Member Posts: 273

    Same boiler as here (and in the thread title):
    https://forum.heatinghelp.com/discussion/188257/end-of-season-report-hows-my-boiler-doing/p1

    The gas-valve is the only adjustable bit from what I can tell. The boiler is super oversized (design-day heat loss is about 25K BTU/hr or so), but I have high hopes for the thermal purge system I added on this summer. You can't try to push BTUs into your house if they've already gone up the flue though!

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,157

    If you are talking about the CG(?) boiler in your previous posts there is no air adjustment on the burner. There is a small hole that you can drop a screw or bolt into to diffuse the entering gas and air

    Screenshot 2024-11-01 at 3.04.19 PM.png

    You can try adding a thin screw that will terminate at about the center of the tube and see it that makes the excess air number drop slightly.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • mattmia2
    mattmia2 Member Posts: 10,754
    edited November 1

    I would be a little concerned about a gas valve that is malfunctioning, if it still has over the 5.5" wc at the valve while firing then something is wrong with the regulator in the valve or the valve itself. Though it is somewhat of a long shot that the valve will stick open as a result of whatever isn't working right, it is a very bad thing if it does so I would be inclined to replace the valve if I see any malfunction. Also if whatever is wrong with the regulator causes the diaphragm to break, a more likely failure, it will leak a small amount of gas which also isn't desirable.

    There should be some sort of an air shutter on the burner which should let you cut the excess oxygen.

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