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boiler pilot light

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nuge0013
nuge0013 Member Posts: 10

I have an old Weil-McLain boiler, CGM series 6, so it's old. We have had no issues in 10 years living here but recently had some kettling issues. A professional used Sentinel X300 (I know, wrong cleaner for the job) and it did improve. We were all set to add X200 Noise Reducer in the fall for the residual knocking because we're not really in temps that require constant running of the system. It just had a replacement of expansion tank, pressure relief valve, fill valve, and backflow preventer, so we invested a lot in it before really knowing its age.

This weekend while it was in a heating cycle, the flames and pilot light went out. I didn't smell any gas at all, but turned off gas and thermostat anyway. We are waiting for our professional to come take a look. In the meantime, what are the possible issues we can prepare for having to make a decision about? Is this boiler as good as dead?

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  • Jamie Hall
    Jamie Hall Member Posts: 23,536
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    The boiler is probably just fine — although if it's noisy it could use a good flush. The problem you are having is something in the gas train or its controls and safeties — and the list is longish, but a real professional should be able to find it.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HomerJSmith
  • HomerJSmith
    HomerJSmith Member Posts: 2,477
    edited May 15
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    When I hear knocking or kettling in a boiler I think of low flow or too high a temperature. The expansion and bursting of vapour pockets. Make sure the air charge in the Ex-tank is 15psi and the fill valve is set at that pressure.

    The pilot assembly probably need cleaning, and the pilot orifice need cleaning on an old cast boiler. So many things can cause a boiler to flame out. Will the boiler re-light?

    https://www.weil-mclain.com/sites/default/files/field-file/cgm-pcg-series-6-manual_1.pdf

  • gyrfalcon
    gyrfalcon Member Posts: 167
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    LP or Natural Gas?

    If LP, is your tank full?

    Any other gas appliances?

    Slant Fin Galaxy GG100(1986) , 2 zone hot water baseboard, T87 Honeywell thermostats. 
    PRR
  • mattmia2
    mattmia2 Member Posts: 9,837
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    is there any water under it? a leak in the right place can put the pilot out but most likely just a worn out thermocouple or dirty pilot burner.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,737
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    It probably needs a new thermocouple

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    as it is with most conventional non-condensing boilers that operate on gas, there is rarely a professional maintenance performed, and there could be years of operation with no noticeable change.


    your CG boiler falls into that category. Not much to go wrong with them, so not much maintenance is completed. Over the many years of operation, there has been a significant amount of buildup that finds its way to the bottom of the cast-iron boiler sections. That is where the Kettling can start.

    I remember a customer who had a Kettling problem that I could not figure out. After years of operation at lower temperatures and other adjustments, I found out that the Spirovent air eliminator was loaded up with sludge and acted like a partially closed valve. This caused the boiler Water to travel slowly through the system and allowing the boiler temperature to become extremely high closer to the burners while the Aqua stat near the supply pipe was set at the appropriate temperature to operate the system. It turns out the Kettling was just the water becoming too hot at the bottom of the boiler.

    I would suggest that someone take the bottom fitting from the boiler and look through it with a flashlight to see How much sediment is lying on the bottom of the cast-iron sections.

    Edward Young Retired

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

    HomerJSmith
  • HomerJSmith
    HomerJSmith Member Posts: 2,477
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    Possibly, you could open the boiler drain valve and flush the boiler sections thru a garden hose.

  • nuge0013
    nuge0013 Member Posts: 10
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    Thanks for all of the replies! This is encouraging. To answer some questions:

    -Yes, ex-tank is set to15psi and the fill valve is set at that pressure.

    -When all of the parts were replaced about a month ago it got a good cleaning

    -No water that I could see was present

    -Natural gas, and other gas appliances are working fine

    The professional hasn't made it out yet, so still waiting on his assessment. It's helpful to hear about the thermocouple. What's a typical price to expect to replace one of those?

  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,020
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    Discussing pricing on this forum is a No-No. Against the rules.

    Erin Holohan Haskell
  • HomerJSmith
    HomerJSmith Member Posts: 2,477
    edited May 17
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    Thermocouples need replacing as the voltage that they produce is inadequate to hold the gas valve open.

    They come in different lengths and if you replace it, replace it with one which is the current length. At the same time clean the pilot assembly and set the pilot flame to the correct pressure and flame height. That is done with the pilot pressure adjustment in the gas valve.

    You can get thermocouples in most hardware stores, just choose one the matches and mounts in the pilot assembly as the old one. There are universal mounting type that have all the parts in the kit to match your mounting configuration.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited May 17
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    At that Series 6 age, you may have the more common Thermocouple that just about every HVAC or Plumbing tech keeps on their service truck.  Or you may also have the 750 Millivolt Pilot generator.  Both measure the existence of a pilot flame with a thermocouple bulb that sits in the flame and generates a very small amount of electricity, when heated by the flame.  If your gas valve is of the millivolt variety, then that may or may not be on the repairman’s service truck since they are not as common.  

    Either way, on a WM CG boiler, they are fairly easy to replace and therefore the price of the service call may be a minimum labor charge and cost of a part that is inexpensive plus a markup from the wholesale cost to the retail price.  The pilot generator is usually double the cost of the standard thermocouple.  

    Since we can not post actual prices of repairs and equipment replacement, you can be assured that the cost will be within reason, even with the higher priced providers. Not time to replace the boiler yet!

    Where you may get in trouble is if the age of that boiler is equivalent with rusted nuts bolts and screws the may cause the replacement to become an all day project.

    Try to get the total cost up front before they start the job. When I would quote an up front price, I would stick to it even if the project went a little south and took extra time. Hope you have a reputable service provider.


    Edward Young Retired

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

  • nuge0013
    nuge0013 Member Posts: 10
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    Thank you, HomerJSmith and EdTheHeaterMan for the helpful and detailed replies! You make it sound easy, and I'm pretty handy, but I'm nervous to work with a gas appliance on my own. Is there a way to know if the problem is with the thermocouple or the pilot generator? I am getting a bit tired of waiting for the professional, even if we are in warm weather now.

  • mattmia2
    mattmia2 Member Posts: 9,837
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    can you post a picture of the gas controls?

  • SuperTech
    SuperTech Member Posts: 2,200
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    You can test a thermocouple or pilot generator easily with a multimeter capable of measuring milivolts DC. It's a fairly simple process. If you can post pictures of your pilot assembly we can give you step by step instructions on how it's done. Some guys like to just replace the thermocouple/thermopile and see if it works, a good tech will actually measure the flame current and find out if it's correct.

  • HomerJSmith
    HomerJSmith Member Posts: 2,477
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    Thermocouples are cheap. Rather than test it, change it. When in doubt change it out.

    mattmia2PRR
  • nuge0013
    nuge0013 Member Posts: 10
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    SuperTech, thanks for that offer! Here's a pic. My multimeter is a basic RadioShack model. The DCV side goes from 10 to 500, but it doesn't say whether that's millivolts.

  • mattmia2
    mattmia2 Member Posts: 9,837
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    Is it an analog meter?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    That is an easy DIY fix and you have the standard Thermocouple in the picture. You will need one that is at least 18" long, but to be sure I would purchase a 24". If it is too long , you just coil up the part you done need (or actually don't un-coil it).

    When i do that replacement, I remove both the aluminum pilot tube and the thermocouple from the gas valve. Then I remove the burner that the pilot burner connected to it from under the boiler.

    Replace the thermocouple and then put the burner back in place. be sure to get it in the grove in the rear od the boiler before you place it on the brass fitting near the front of the boiler.

    Edward Young Retired

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

  • nuge0013
    nuge0013 Member Posts: 10
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    Thanks, EdTheHeaterMan. I will look for some videos on this but would like to test it first.

    mattmia2, yes. It's an analog multimeter with the needle that moves and indicates the voltage. There's a dial that I can set to intervals from 10 to 500

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    Here is a video that can help.

    stop at 3:28 the fast foreword to 7:20

    Stop at 7:55 and fast foreword to 9:40

    Stop at 10:00 and fast foreword to 12:00 until you get to 15:21

    This way you don't need to look ai his mistakes and pilot burner cleaning that may or may not be necessary.

    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: 9,837
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    unless it is a vtvm/ssvm it will load the circuit in a way that needs to be accounted for in interpreting readings and it doesn't look like it has a range to read .75 v very accurately. A digital meter is high impedance and doesn't load the circuit in a measurable way (a solid state voltmeter or vacuum tube voltmeter is also high impedance).