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Boiler pilot and main burners going out

JP2347
JP2347 Member Posts: 8
Crown boiler pilot and thermocouple style with vent damper I'm randomly losing the pilot and burners.  I put a new oem stepper gas valve and thermocoupling in and I'm still having this issue.  I retook the pilot assembly apart and still had some fine brown gunk i got out and had a better pilot afterwards.  I thought maybe the flame wasnt enveloping the thermocouple enough but its better and still have same issue.  24 volts at the gas valve still when the pilot and burner both go out.  Rollouts arent tripped and fusible link still operational; there is a chimney liner.  Any thoughts or ideas?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 19,154
    Gas pressure?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JP2347kcopp
  • JP2347
    JP2347 Member Posts: 8
    3.41" manifold, incoming was 5.85
  • HVACNUT
    HVACNUT Member Posts: 4,626
    So everything is running and then suddenly the pilot and burners go out?
    You replaced the thermocouple, but did you check it? A good thermocouple should produce 18 to 25 mv.
    Or there's a wind tunnel in the room.
  • JP2347
    JP2347 Member Posts: 8
    Yes exactly, both pilot and main burners go out at the same time.  I didn't see the likelihood of a brand new thermocouple being bad but I suppose it's possible.  The combustion air is on the complete opposite of the mechanical room
  • HVACNUT
    HVACNUT Member Posts: 4,626
    What's a stepper gas valve? You're sure it's a direct replacement?
  • Shane_2
    Shane_2 Member Posts: 176
    I would check the gas pressure again with other gas appliances running.

    Had a similar problem last year, ended up being the regulator at the gas meter. Your pressure seems pretty low to start.
  • HomerJSmith
    HomerJSmith Member Posts: 1,625
    edited March 9
    Any other appliance drawing gas when this occurs? If you lose the pilot, you will lose the burners. It may be a grounding issue. I would ground the gas valve, many will have a 1/4" grounding tabs. I would try a jumper from the gas valve to a solid part of the boiler frame and see what happens.

    I guess this is a standing pilot rather than an intermittent pilot? If an intermittent pilot look to the module.

    Of course, any interruptions in the 24V safety circuit will also kill the gas valve. It could be a bad micro switch in the damper or loose connection. Jump all your safety devices one at a time and see what happens. You can use a multi meter and test the safety devices. But, you say that you have 24V at the gas valve when the failure occurs, so I would expect that the safety devices and wiring are ok. When ever i assume something, I make big mistakes. Assume but verify.
  • JUGHNE
    JUGHNE Member Posts: 9,824
    Your pilot light is self sufficient in remaining lite.
    Only t-couple failure or wind blowing it out would shut it off.
    Sometimes when the main burner lights that can push the pilot flame away from the T-couple. But most T-couples will carry enough holding current for 30+ seconds to keep the pilot on. And the flame of the main burner would relight the pilot burner.

    If both pilot and main burner drop out, I would suspect gas pressure as stated above
    by Shane. NG regulator may be falling down with load.

    Rare happening is for the vent on the outside regulator to ice over and shut down the gas or nearly so.
  • HomerJSmith
    HomerJSmith Member Posts: 1,625
    edited March 10
    Perhaps we are looking at the wrong thing, the pilot, the gas valve, the regulator, etc. when we should be looking at what controls the gas valve.

    Whether it is standing pilot or intermittent pilot is important in diagnosis as the controlling factor are different for each one. In standing pilot, the thermocouple or Powerpile control the pilot valve and the pilot flame is operating 24/7. In intermittent pilot, the pilot and burner flames are controlled by the board or module.

    The reason that I bring this up is because in the last few months I have come across this situation:

    I was called out after another tech diagnosised the problem as the gas valve for the inoperative furnace. It was, he said with great confidence, the 5 wire gas valve and they don't make those anymore. It was, on closer inspection, the ignition module. It had a solder break on the board relay.

    Recently, another company replaced a gas valve on a furnace that operated intermittently, convinced that was the problem. The problem persisted. I discovered on closer inspection the there was a solder break on the board that controlled the 24V to the gas valve. I can't tell you how many times that I have encountered this problem.

    Two missed hits at a cost to the customer.

    I suspect that jp2347's has an intermittent pilot sys because both go out, pilot and burner flame. I would check the module or what is controlling the gas valve.

    That's my take and as Alan says, "Often wrong, but never in doubt."

    When I clean the pilot, I take out the top hat, burner orifice, and I have a very fine needle that I use to make sure that the orifice hole is open and not plugged. The pilot flame should be blue and not orange.

  • JUGHNE
    JUGHNE Member Posts: 9,824
    JP2347 said:

    Crown boiler pilot and thermocouple style with vent damper I'm randomly losing the pilot and burners.  I put a new oem stepper gas valve and thermocoupling ----the thermocouple---- 24 volts at the gas valve still when the pilot and burner both go out.blockquote>

    I am thinking no ignition module....standing pilot with T-couple.

    HVACNUT
  • mattmia2
    mattmia2 Member Posts: 5,742
    Is this standing pilot or intermittent pilot? If it is standing pilot, does the pilot ever go out when the burner isn't firing?
  • HomerJSmith
    HomerJSmith Member Posts: 1,625
    If I had the model # I could have answered my own questions. It beats going down the wrong track.
    mattmia2
  • Tim McElwain
    Tim McElwain Member Posts: 4,517
    Lets start at the beginning. Gas Pressure at 5.85 almost 6 which is what it should be if it is in a high pressure area. The house regulator outlet pressure is 6 " W.C..

    I would take some millivolt readings Normal around 30 open circuit 15 closed circuit and stable at 15 with the system running. The drop out on the magnet assembly should be Below 6 1 to 2 is normal.

    What is an OEM stepper valve? Do you mean a step open valve? If so what was the make and number of the valve you replaced and what is the make and model of the valve you installed?

    What are the numbers on the pilot?

    What size is the pilot orifice a typical size for natural gas would be an .018.?

    Have you conducted a combustion test with a combustion analyzer?

    kcoppEdTheHeaterMan
  • HomerJSmith
    HomerJSmith Member Posts: 1,625
    This doesn't make sense to me. On a standing pilot sys the pilot (30mv) is separate from the main gas valve operation 24V. The problem remained after the new gas valve was installed indicating that the gas valve isn't the problem. If there are 24V at the gas valve when a failure occurs, then the only thing that could shut down the main burners is a failure of the pilot thermocouple voltage to the gas valve.
    EdTheHeaterMan
  • mattmia2
    mattmia2 Member Posts: 5,742

    This doesn't make sense to me. On a standing pilot sys the pilot (30mv) is separate from the main gas valve operation 24V. The problem remained after the new gas valve was installed indicating that the gas valve isn't the problem. If there are 24V at the gas valve when a failure occurs, then the only thing that could shut down the main burners is a failure of the pilot thermocouple voltage to the gas valve.

    Or insufficient dynamic gas pressure and everything goes out.
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,342
    edited March 11
    More to the point starts right after "Long Story Short" below

    Different story with same problem. Had a 200 year old house with a boiler and water heater in the original chimney. No liner (not even terra-cotta tiles, it's that old). Repointing on the chimney was long overdue. The chimney was at least 35 feet above the flue connector for the water heater, which was just above the boiler vent connector. The grandparents were living in that old barn. My customer was the grandson. Got the call about the pilot on the water heater would go out. One of my technicians cleaned the pilot and replaced the thermocouple. A few weeks later and no hot water again. My son responded and relit the pilot and found nothing wrong. Another few weeks and no hot water again. The pilot was out and the grandson lit it. I then suggested the Robert Shaw pilot relight kit (https://www.amazon.com/Robertshaw-785-001-Carrier-Automatic-Relight/dp/B000LDHK4U)

    Problem solved.

    A few years went by and the problem started to present again. The chimney still needs repointing and has more gaping holes in the mortar joints. Told customer to get a liner, so he called a chimney man Don, and spent $ C.00 (think roman numerals) the cheapest (uninsured) guy in the phonebook. Don stuck a mirror in the chimney base and said, "Nothing wrong here!"

    What was wrong is that when the wind was blowing in a certain direction, there was a very powerful down draft that blew the pilot off of the thermocouple. I informed the customer on how chimneys worked and that the chimney sweep was incompetent and he wasted the payment. "You either need a liner or a direct vent water heater." The water heater was less expensive.

    Since the house was going to be renovated after Grandma and Grand-pop passed on, Which could be any day now... (CO poisoning and all)... they didn't want to spend any money on the chimney or the water heater for that matter. The boiler controls were direct ignition so even though the downdraft was still a problem, it lit every time there was a call for heat. The boiler and water heater was located in a shed porch add on room (probably added in the 1940s when indoor plumbing was connected) so I was less concerned about CO because the room was more of an outdoor porch with a shed roof, then an enclosed room. I think the broken glass in the wooden door was also a factor.

    Long story Shortt (I know too late for that) You could pit a "bandaid fix" like that relight kit. Or you may have a high draft condition with that great new working chimney liner that is pulling the pilot off the pilot burner. My vote is to find and fix the problem. You might want to get yourself a GoPro camera and set it up to watch the pilot flame to see if and when it pulls off of the burner, away from the thermocouple.

    After thought
    Is your thermocouple equipped with a spill switch that breaks the MV circuit? This is a picture of one type of adaptor.
    Some Gas Valves have then built in. @Tim McElwain would be more familiar with this component and its use on standing pilot systems. Can you get a model number from your gas appliance or a picture of the gas valve. Close up and from about 18" away and 6 feet back?



    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • HomerJSmith
    HomerJSmith Member Posts: 1,625
    I made several comments with no feed back. To reiterate, What color is the pilot flame? Is it a normal flame or a weak flame? I think all exhaust vent terminations should have a vent cap terminated at the appropriate height above the roof line.