Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Utica MGB100HD Pilot Goes Out

Brad White
Brad White Member Posts: 2,393
Hey all-

I need the collective minds to help solve a problem for a former student of mine. He and his fiance' just bought their first home, a condo, served by a Utica MGB100HD installed in 2005. They moved in about a month ago.

In the past two weeks the pilot has been out in the AM and does not last a cycle. I have asked Alex to take a look, to watch it between cycles, but also want to get an idea of what might be going on. He is down there to re-light it often enough, why not hang around a bit?  :)

 This has a standing pilot and a vent damper which is wired to stay open. (Have asked if it has "the hole" while I am at this.)

He called in a service company who replaced the thermocouple, the gas valve and now thinks it may be the aquastat which, as far as the pilot going out, makes no sense to me. Problem persists. I want to help steer him and his tech, knowing my own limitations of course. Have not seen the place yet, just got word, so what is above is all I know right now.

I should get over there this weekend to check draft, any local exhausts, dryers, etc. but also know the place is older and not well insulated, pretty drafty they say, so doubt a lack of combustion air but nor ruling anything out

Thanks in advance!


Edit: In Alex's own words:

"The pro replaced the gas valve, and noted that the vent damper was set manually

open. When he set the damper to automatic, the boiler would not fire. He was

going to replace the damper and motor, but noted that they worked fine when he

tested them outside the system. Further diagnostics lead him to believe the

issue is some sort of intermittent connection/fault in the aquastat relay.

So the pro left the damper manually open for

now, and believed that the pilot should stay lit with the new gas valve, but

that hasn’t worked out. There are two theories of what’s going on now: either

the intermittent connection in the relay is causing the system to shut itself

off randomly, or the open damper is allowing some sort of draft to put the

pilot out. His proposed next step is to replace the relay, but we’re not sure

if that will solve the problem or not."
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

-Ernie White, my Dad


  • Tim McElwain
    Tim McElwain Member Posts: 4,556
    The first thing I

    would do is recheck the thermocouple system thoroughly using the attached procedure which is also available in the Resources section in the Library in Tim/s Closet.

    It sounds like someone is throwing parts at tho problem and it is not getting fixed.

    What is the damper plugged into? I assume it is the relay, if so the connection on the relay had to be jumped out in order for it to work at all if you need the procedure for jumping out the primary control let me know.

    Here is the t'couple procedure:



    I am often asked about troubleshooting a thermocouple on gas systems. This will be a permanent reference that will give a step-by-step procedure.


    A thermocouple is a device used to satisfy pilot safety on many 24-volt gas systems. The thermocouple is a device made up of two dissimilar metals. They are joined together at the tip (Hot Junction). When heat is applied to that hot junction a small millivoltage is created. This develops because of temperature difference between the hot junction and what is called the cold junction. The flame has to envelop the upper 1/2" to 3/8" of the thermocouple and the tip should glow a "dull red". If the flame is adjusted to a sharp flame it will glow "cherry red" this will cause the tip to be welded and eventually the thermocouple will fail. The flame should be adjusted to a soft blue flame, not roaring or lifting. The normal millivolt output is 25 to 35 millivolts, on some you may even get up to 35.


    The other part of this safety pilot system is the electromagnet (power unit). It is if you will the LOAD and we can say the thermocouple is the SOURCE. The electromagnet is made up of a coil of wire and "U" shaped iron core. When the thermocouple is heated and the millivolts generated the coil will be energized and create a magnetic field. The magnetic field will cause the "U" shaped iron core to be magnetized; it in turn will hold open a seat allowing gas to pass through.


    When this system malfunctions it typically causes the pilot to go out and the gas will not flow. The first thing that should be done when arriving at a pilot outage situation is to do some visual checks.









    Once those things are addressed it is a good idea to take some millivolt readings. It should also be mentioned that many times it is the policy of some to replace the thermocouple on a call and clean the pilot. It is not a bad thing to do, however it is statistically about 85% of the time it is the thermocouple giving the problem. It is the other 15% of the time that taking readings can solve other problems.


    You need a multimeter with a DC volt scale, as the millivolts generated are DC volts. There are four readings we are going to take they are


    OPEN CIRCUIT - this is taken with the thermocouple disconnected and the meter leads attached to the outside of the thermocouple and the other meter lead attached to the tip of thermocouple. The pilot-on-off knob will have to be held manually to take this reading. This measures the output of T'couple the readings must be above 17 to 18 millivolts.


     * CLOSED CIRCUIT - This measures the millivolts used by the coil in the electromagnet. A rule-of-thumb is this reading should be roughly half of the open circuit. It is taken using an adapter screwed into the magnet and the thermocouple screwed into the adapter.


    CLOSED CIRCUIT LOAD - This reading is taken the same as the previous reading except the burner is now on. With a proper flame this reading should be about the same as the previous reading. With a lifting main burner flame or excessive drafts or chimney pull, this reading may reduce from previous reading (flame being pulled away from the thermocouple). With the cold junction being heated this reading may increase. If the "cold junction" is heated excessively it will break down.


    DROP OUT - This is the final reading. It requires the pilot to be blown out. It measures the ability of the magnet to hold under reduced MV input. A good unit should drop out below 6 MV's - normal is 1 to 2 MV's. The allowable "drop out" time is 180 seconds yes three minutes. It is more likely to be a minute and half to two minutes. There will be an audible "click" when the magnet shuts down.




    A normal set of readings


    OC- 30 millivolts

    CC- 15 millivolts

    CC(load) -15 millivolts

    DO- 1 millivolt


    The best way to be able to diagnose these readings is to use MILLIVOLT CHARTS these can not be displayed here but I can provide them if you e-mail me.


    Thermocouples from different manufacturers vary as to their dependability. The only thermocouples I recommend are made by Johnson Controls. The K15 and K16 series are the best. If you are having durability problems then use the K16RA, which is a nickel-plated high ambient or corrosive environment thermocouple. The Husky (K16) will fit most applications and for those that it does not the Slim Jim (K15) will fit.


    To repeat the adjustment of the pilot flame to envelope the upper 1/2 to 3/8 of the thermocouple is important, the flame should be a soft blue flame not roaring which will cause the tip to glow a "dull red" versus "cherry red".


    The combustion condition (excessive temperatures) in the chamber is also an issue and this will require a combustion test and draft measurement to insure that excessive temperatures are not being applied to the pilot. In some cases on water heaters it may be necessary to alter the pilot adaptation to get better quality performance. This however should not be done unless you have had proper training.


    The possibility of the equipment operating in a depressurization environment will certainly lead to thermocouple failure. In addition if the equipment is flued together with a "fan assisted" furnace or boiler this can lead to problems. There are solutions to this also but training is required.


    The thing that I find is often a problem is the environment in which the equipment is operating. Many times corrosive chemicals and airborne contaminants are being drawn into the air gas mix and a chemical reaction takes place. This again requires attendance at a training session by a professional combustion person to help you to see the various affects this will have.


    Last of all the failure to put all the doors and covers back in place on equipment. The failure to do this will cause an alteration in combustion air and the flame stability is affected.


    The design of some equipment is also a problem. When there is high demand for heat (very cold weather) the temperatures that are created in the chamber have an adverse affect on the pilot and thermocouple system. The addition of the K16RA thermocouple can offer some assistance toward extending the life of the thermocouple in this situation.


    Insufficient air for combustion and dryers operating in close proximity to equipment also lead to problems.


    Last of all and this is not directed at any one in particular but just plain lack of service personnel and installers knowing what they are doing.


    My book "Circuitry and Troubleshooting" Volume II addresses many of the things in question here.

  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Things that will cause pilot outages...

    A lack of draft through the combustion zone (plugged heat exchanger) allows so much CO2 to accumulate that it completely snuffs the main and pilot flame (rare, but possible).

    A cold stack condition that the boiler can't overcome that spills products of combustion into the room and snuffs the main and pilot lights (seen this a few times in my years of service)

    Pilot snuffed on burner extinguishment. More common than not, and can be an indication of need for service (plugged orifi) Can be fixed by either servicing and adjusting pilot per Tim's attachment, and worst case scenario, place a pilot re-lighter to rectify the situation.

    Pilot outage, especially standing pilot, is not affected by any of the other electronics packages. I agree with TIm. Someone is throwing parts at a problem in hopes of resolution. AN expensive and frustrating means of trouble shooting...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • AlexMatthews
    AlexMatthews Member Posts: 5
    An Update

    Hi Everyone,

    Thanks so much for your thoughts on this! I've been observing the problem a bit further, and thought I'd give an update.

    From a cold start, lighting the pilot yields a steady flame which properly envelops the thermocouple, which glows a deep red. The thermocouple has been replaced twice now; first by me, then by the tech.

    When the boiler is shut off after an extended firing, the pilot wavers, and does not envelop the thermocouple. A few minutes after the boiler stops firing, the gas valve will click and the pilot is extinguished. This did not occur after a few minutes worth of firing, only when I allowed it to fire for half an hour or so.

    I thought at first that the hot flue, combined with the manually open damper, was creating a draft which was pulling the pilot flame away from the thermocouple. I decided to test this theory, by manually closing the damper while only the pilot was lit. When I re-lit the pilot, before closing the damper, the flame was steady again, and has stayed that way.

    It would seem that it's not a draft. There seems to be something restricting the flow of the pilot when it's lit through an extended firing of the boiler, but which is remedied by just a minute or two of being put out.

    So is this a matter of a clogged or constricted pilot? Replacing that was the next plan of attack. This boiler had a revision which increased the size of the pilot orifice, so the plan was to install the revised part.

    For what it's worth, I just spoke with one of the other condo owners; he told me that we were misinformed as to the age of the boiler. The boilers were installed 10-15 years ago, prior to the condo conversion of the house.

    Thanks again!

  • Tim McElwain
    Tim McElwain Member Posts: 4,556
    Throwing parts at

    problems never solves the problem just keeps the parts store in business.

    What are the millivolt readings, gas pressure readings, combustion testing results? With out those why keep putting in parts hoping the problem will go away.

    The procedures I gave is how these systems are tested.
  • RobbieDo
    RobbieDo Member Posts: 131
    Parts Replacers

    Unfortunately there are many companies that are " Parts Hangers " either the tech does not know how to test things or the company does not have the proper training. Training is a on-going process.

    To your issues, as Tim said you need to check gas pressure, millivolts on thermocouple, combustion test, is the pilot tube clean? All of these must be checked.
  • Steve Whitbeck
    Steve Whitbeck Member Posts: 669

    Just replace the pilot assembly.

    Make sure it has the right orifice .

    sounds to me like you don't have a good crisp pilot flame and because of that it doesn't relite properly when the main burner goes out. You may also check to see if the pilot is mounted properly. Sometimes when the burner goes on or off it can put the pilot out if it is not mounted in the correct spot.
  • Wavering Pilot

    I once had one like that and it drove me crazy for a while. It was a little bit of water in the small pilot line.

    Thanks, Bob Gagnon
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Water in the small pilot line.

    I once read a copy of the New York City plumbing code -- from the late 1800s. It was fascinating. One part was about plumbing gas, back in the days where if you wanted gas, you usually had to make your own. One way was to have a big bellows with a weight on the top blowing through a tank of gasoline buried in the ground. The air bubbling through was piped through the house. The gas was used mainly for lighting in those days. Some people could get manufactured gas which, if I remember correctly, was largely carbon monoxide. Good enough to light a lamp.

    They explained how to run the pipes, the importance that there be no traps, especially accidental ones. Because a gas lamp would go out if the gas were blocked by some condensate. As the gas bubbled through the water, the light would go out, and then the gas would resume. Explosion and suffocation hazard. I guess you could smell the gasoline vapor if you were awake, but if you had manufactured gas, you probably could not smell it.

    They even had gas lamp chandeliers that could be raised and lowered without leaking. You needed to keep water in there; its weight would help it seal the moving parts. I am glad we have electricity now.
  • Brad White
    Brad White Member Posts: 2,393

    "If you wanted gas, you usually had to make your own. One way was to have a

    big bellows with a weight on the top blowing through a tank of gasoline

    buried in the ground."

    Proof that the Dead Men had the vision to start their own space program.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • AlexMatthews
    AlexMatthews Member Posts: 5

    The current arrangement of the pilot line does create a trap between the gas valve and the pilot orifice, so if water or condensation had managed to get in there it would never escape. I'll see if I can do anything about that when I get home from work tonight.

    The tech is scheduled to return on Thursday. I've sent him the list of various tests that you've all suggested, for his review and comment. I'm not sure which of them he may or may not have performed previously.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Dead men were not so dumb...

    I could not remember the whole book. They did advise to treat that gasoline tank as though it contained the entire amount of energy that the essentially carburetted gas that came out of it. That due care was advised. And the tank was buried in the ground. But otherwise, they were burning candles, whale oil, or kerosene in their lamps. Think of the convenience of gas lamps. I lived in a house in Buffalo, NY, in the 1940s that still had the gas pipes in the walls for the lights. They were disconnected near the gas meter. The house had hot water heat, coal furnace. The first house I lived in there had convection hot air with coal burner. The third had forced hot air with a coal burner that my dad had converted to gas after W-II ended. You were not allowed to burn gas for heating before that because there was not enough (manufactured gas until we got natural gas after WW-II).
  • Pilot Line Condensate

    I simply disconnected the pilot line and blew air through it, got a drop or two of water out, that solved my problem.

    Thanks, Bob Gagnon
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • AlexMatthews
    AlexMatthews Member Posts: 5
    edited March 2011
    Unfortunately, that doesn't seem to have been the problem

    There was no sign of water in the line, and the problem persists. But thanks for the idea!

    The blow-outs are definitely related to firing the boiler. After the condo came up to temp last night, I re-lit the pilot. It's been warm (for winter in Boston), so the boiler didn't fire during the night. The pilot stayed lit through the night, but went out after firing the boiler to bring the condo back up to daytime temp.
  • AlexMatthews
    AlexMatthews Member Posts: 5
    Heard from the tech again

    He's been in further touch with the manufacturer, who has confirmed that this is a known problem with this model of boiler. It doesn't effect every boiler; you could have five of them, and only have trouble with one. It turns out the revised pilot they came up with is not simply an enlarged orifice; it is completely redesigned. They found the problem was caused by the old horizontally oriented pilot, and the fix is replacing it with a vertically oriented pilot assembly.

    The tech ordered the new assembly, but it's been delayed, so we'll have to wait until Monday for the fix.

    Tim: by the way, the tech tells me he's actually taken your course.

    Thanks again for all your help, everybody. I'll let you know how things go on Monday.
  • Dealing With the Utica Tech

    I should have thought of that, it takes about a minute to get through to someone who will give you the correct answer. Utica is a great company to deal with.

    Thanks, Bob Gagnon
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Tim McElwain
    Tim McElwain Member Posts: 4,556
    If you go to

    ECR International (Utica) site there is a Technical Bulletin on this change the number is Bulletin No. 080708.

    It is at www.ecrinternational.com/secure/upload/document/1512.pdf

    Also another  bulletin on orifice change bulletin No 3607U.
  • AlexMatthews
    AlexMatthews Member Posts: 5

    The new pilot assembly has solved the problem. Utica's solution seems to have been to just throw extra fuel into the fire... it's more like a rocket engine than a pilot. I pushed the tech, thinking that the thing was turned up too high, but he actually spoke to Utica tech support to confirm that he'd calibrated it properly. They apparently designed the replacement pilot to have a roaring flame, just to make extra certain that it won't go out.

    Anyway, the pilot has remained lit since yesterday, through multiple cycles, so all is good. Thanks again for all your input!
  • Brad White
    Brad White Member Posts: 2,393
    That is

    awesome, Alex!

    Nice to have that behind you. I was going to check in and see how things were going, so good timing.

    No crystal ball here, but you should get at least another decade to 15 years out of that boiler. No jinx though!

    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • ScottMP
    ScottMP Member Posts: 5,884
    This has been very helpfull

    As I have had a customer with this same problem on the Same boiler and model for a few years, Sometimes it goes months with out a problem ... sometimes twice a year.

    I will now order them the new pilot assmbly. Which by the way was where I was heading ... no really :)
  • Pilot

    Hey Scott, good to hear from you, I've been busy. Brad, the Utica MGB should last many decades, I have had some in for decades, never replacing one.

    Thanks, Bob Gagnon
    To learn more about this professional, click here to visit their ad in Find A Contractor.
This discussion has been closed.