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Old School Thermocouple/ pilot question

Hi there Heating Help Gang...

I am a homeowner who is not in the HVAC business. I am having trouble getting the standing pilot light adjusted on my old round boiler. Something is definitely different than normal. It has a millivolt gas valve, from what I have learned over the years. The pilot light unit itself has a thermocouple-like device screwed to it, which I think is part of the millivolt thing. Sorry if I am getting this all wrong. I will post a couple pictures to clarify.

When I first lit the pilot, the flame was so small, even when I opened the pilot light valve all the way, which it is never set at. I decided to clean it, like I have seen my boiler guy do a couple of times. I am handy, so thought there would be no problem.

I removed the pilot unit from under the burner and wrangled it gently to a position where I could clean it, near the opening at the bottom of the boiler. I used a toothbrush, dust-off, and scraped a little with a knife to remove scaling on the thermocouple thing. I put it all back in place, and when I lit it the flame was definitely much bigger, but out of control and yellow.

I pulled it back out again, and lit it and could first off see a leak at the connection where the gas line enters the pilot unit. I managed to correct it by tightening the fitting, and I remember my boiler guy having to mess with that too, so nothing new there.

However, I noticed there was gas (flame, when lit) coming out of a hole that I never noticed before in the base of the pilot unit. Upon very close inspection I could see that the hole is not threaded, so nothing came unscrewed. I thought maybe it is a vent hole to control air/gas mixture. I also thought maybe it was plugged with plumbers putty and maybe that fell out when I hit the unit with the compressed air.

I decided to try covering the hole and lighting the pilot, and that gave a much more normal looking flame, except that the pilot unit was in a horizontal positon at the time, and it is normally in a vertical position. But I did not think of that. I decided to put a screw in the hole with a tiny daub of thread sealant, and then reinstalled the pilot unit. When I lit it, the flame was still not right. It was very yellow, and was not the shape I remember it to be. I removed it and took the screw out, but now I am stumped.

Can anyone look at the attached photos for me, and let me know what that hole is for? Keep in mind if you notice thread marks in the hole, it is from my screw. One photo shows the unit with my screw in place. The other two show the unit from two sides, and the hole is visible in the right side view. Any input of course is appreciated. Please do not convince me to buy a new boiler. ; ]

Thank you,



  • icesailor
    icesailor Member Posts: 7,265
    edited October 2012
    Well meaning:


    You are a nice guy but you are in over your head. You could get dangerous. Please get a professional to correct what you have done. Had you not gone as far in one step, someone here may have helped you in the next step. But you went past there and may have created a situation that some here would not want to be responsible for trying to help you out of a bad situation.

    Call a Professional. You may need new parts.

    In my opinion.
  • Jerry Mann_2
    Jerry Mann_2 Member Posts: 13
    I'm nice, but not stupid...

    Thanks for your opinion, IceSailor. For the record, my pilot is not in any worse condition than when I started: it began the heating season looking like crap, and it still looks like crap. For the record, while I am a pretty nice guy, I am not clueless. I know my boiler; and its dedicated shut off switch is in the off position. I am not about to do anything that puts my home in danger and I am not out to sue anyone for their advice.

    The thing is, I like to understand how my equipment functions. I approached this forum as a place where people can come for help, especially considering that Dan Holohan has dedicated his life to educating the public, I had hoped to get a reply that explained to me what equipment I have, what to look out for, suggesting what I could do on my own, and what I should avoid doing. Like, "Hey Jerry you have 1954 Warner Swasey thermo-bob, and those always used to go out like that, and you might want to switch it out with a blankety blank", Or "that hole is supposed to be plugged." or "that's a vent hole, you idiot; you have something else going on."

    I don't mind being called an idiot, as long as I learn something from it... I fully understand, and respect, when a pro says I am in over my head, especially when that advice is backed up with some information. I hope someone is willing to look at the photos I took the time to post and offer some information. If not I might do something really rash--like set fire to my Dead Man's ball cap. : ]
  • JStar
    JStar Member Posts: 2,752
    edited October 2012

    Do not plug that hole. It sounds like the pilot orifice fell out while you were taking it apart. Look under the boiler for a little brass bell looking object.
  • Old School 2H pilot safety

    Jerry ,

    The pilot safety you are showing in the photos is certainly a very old school assembly . The 2H White Rodgers bi-metal pilot safety works on the principal of a bi-metal element and switch. The pilot light heats the bi-metal element thus causing it to expand and completing a circuit , proving pilot light . Manufacturers such as Bryant utilized this type of pilot safety in many of their gas warm air furnaces of years ago.

     As far as the pilot itself , it would seem that at first the pilot could have been dirty or partially obstructed considering how you explained the poor pilot flame.

    As suggested by other professionals here responding to your post, you might have disturbed the pilot orifice when you removed the pilot assembly . In addition there are of course many other situations that can cause a poor pilot as you explained .

    The availability of the 2H pilot safety is scarce at best or even available . Depending on the age and condition of your heating system an upgrade might be suggested , or at the least an upgrade of the safety and ignition system of your heating system .

    I hope this is the information you were looking for as you suggested in your post .
    He who knows WHY

    Shall be master of

    He who knows HOW
  • Jerry Mann_2
    Jerry Mann_2 Member Posts: 13
    edited October 2012
    Solution: spider web in pilot orifice

    JStar and helpingothershelp, I appreciate the advice. After spending a lot of time researching and scratching my head, and about $110 in new parts, it turns out there was a spider's web/nest down inside the pilot assembly. My neighbor suggested taking it apart further than I had to clean it, and sure enough there was the obstruction. We cleaned it and reassembled everything and had a perfect, blue flame just like the "good old days." Ha!

    My dad, in the case of our old camper, always talked about those damn spiders nesting in the pilot or burners, and I think every year he had to disassemble the pilot light for the hot water/ furnace on the camper, and clean out the spider web. He is turning over in his grave that I didn't immediately suspect that for my boiler's trouble in the first place. Next year at the end of the heating season I am going to leave the pilot burning.

    Re: replacing and upgrading the burner and safety, the parts I bought from our local supply shop (Woodhill Supply, Cleveland) were I believe a White Rodgers 314 Pilot and a 750 mV thermocouple (plus misc fittings). The new apparatus' configuration was such that I was looking at having to fabricate a custom bracket to position the pilot light precisely in the burner's gas stream. Even my neighbor, who has extensive experience with this stuff, was leery about getting it just right. So we opted to leave the old equipment in place. It has worked since God only knows when... probably original equipment when the boiler was converted to gas in 1932. I hope it keeps working another 80 years. I may keep the new parts as a back up in case the old stuff ever does fail.

    @helpingothershelp, thank you for the extensive info on the WR bimetal strip. And you called it regarding the dirty pilot orifice. @JStar, you were right to not plug that hole, as the pilot is now working fine with the hole wide open--but with no extra orifice fitting. I did search in the pile of dirt at the bottom of the round boiler (God knows what is in there!), but saw nothing that would have fit in the hole.

    Re: replacing the whole heating system, I consulted with an old timer, who learned from his father, in the HVAC business who continues to specialize in steam systems. This was about 2 years ago and he was recommending keeping my round boiler in service, but upgrading several aspect of it, including an energy efficient flue damper arrangement, and a 2-stage burner, controlled by an end main line temperature sensor. Those upgrades, plus a complete cleaning of the boiler vessel and piping, he felt would take maximum advantage of the massive cast iron body's heat-holding capability, and increase my efficiency, giving me a system that has great longevity if properly maintained to his specs. I have not employed his advice for budget reasons.

    Thanks again for your help,


    [edited for clarity]
  • Tim McElwain
    Tim McElwain Member Posts: 4,588
    Good catch spiders can

    create real problems.

    A little education, you do not have a thermocouple operated system nor is it 750 millivolts. It is a Bi-metal pilot which works on the principle of two dissimilar metals bonded together and when heated the one with the greater co-efficient of expansion will bend and this actually makes a switch built into the pilot. This switch is wired into the 24 volt power feed to your gas valve. The timing on that is around 25 to 30 seconds from the time the pilot is lit. If the pilot goes out or gets dirty the system will shut down in about 30 seconds. I would imagine that your pilot is fed gas directly from a small valve attached to a larger valve which controls the main flow of gas. That small valve is a "B" valve we call it and it controls the pilot gas. If not that then the gas is fed somehow from the gas valve (more pictures and the Make, Model and Serial number of your boiler would help( also what are the numbers on the gas valve and the manufacturer?.

    The hole on the pilot you kept trying to seal is the air opening for air to mix with the pilot gas top insure a blue flame.

    I would not venture into trying to alter this system as you are only throwing good money after bad. If you have a forced hot water boiler an upgrade would be best to a Modulating/Condensing 90 + efficient boiler. If it is steam a good oil boiler designed for steam and then convert the boiler to gas with a gas conversion burner.

    Hope this helps!
  • Jerry Mann_2
    Jerry Mann_2 Member Posts: 13
    You are right-on, Tim

    You are right, we do have a small "B" valve that feeds the pilot. And I knew the safety control was called a bi-metal strip, but somehow thought that was the same in essence as the 750 millivolt safety. I did learn online that the 750 mV unit is a bunch of thermocouples bunched together that generate voltage. One question on that: would a 750 mV safety control work in place of my bi-metal safety control? Another question: Do the bi-metal unit fail, and what are the consequences if/ when they do fail?

    Here in Cleveland, everyone seems to run their boilers on natural gas. Our city of Cleveland Heights has a plethora of homes heated by boilers, as the housing stock is all early 20th century. Our house was built in 1926 and has a one-pipe steam system. It was coal for the first couple years, but by 1932 it was converted to gas... and this may be the original conversion burner, pilot and bi-metal safety.

    I will attach photos... I have a bunch to show you. It is a beauty! Try not to be too horrified by them... when I posted them on this forum a year or so ago, I thought you guys were about to send a posse out to shut my boiler down. It has been inspected by two separate reputable steam heat specialists. Also, since the photos were taken we have a low water cut off and the steam damper regulator was taken off due to leaking. We are looking into a flue damper. It would be great to get more background information on the boiler, burner and the companies that made them.

  • Tim McElwain
    Tim McElwain Member Posts: 4,588
    Jerry, what you have is an "old" atmospheric

    conversion burner installed into what was as you mentioned an old coal steam boiler. That burner was made locally in your area in Cleveland and is probably not in business anymore.

    It would be best if you start to think about getting a new boiler. A conversion of that boiler to 750 millivolt powerpile would cost including parts and labor over what is reasonable. We do not discuss price here on the site but if you contact me I can tell you just what the parts would cost and at least estimate the labor.

    A good oil steam boiler purchased and remove the oil gun and install a power gas conversion burner into that oil boiler is my recommendation.
  • Jerry Mann_2
    Jerry Mann_2 Member Posts: 13
    You say "conversion" to 750mV?

    Thanks again, Tim. Are you saying that the 750mV Powerpile Generator (Honeywell Q313 A 1170)  I was going to use actually was not compatible with my system-- I couldn't just swap out and hook up the two wires? The plot thickens... I was sold that part by an industry supplier as a replacement, with no word about doing a special conversion. I was going to have to build out a special bracket to hold the new pilot and Q313.

    I don't know when we will see the cash to replace this boiler.

    ... thanks again for all your help!
  • Tim McElwain
    Tim McElwain Member Posts: 4,588
    Jerry the powerpile

    system would require in addition to the Q313 generator a gas valve VS820A along with a complete revision to your gas manifold as the VS820 has a built in pressure regulator. You would be eliminating the 24 volts as all the controls would have to be wired for the millivolts or if not then a relay would have to be installed.
  • Jerry Mann_2
    Jerry Mann_2 Member Posts: 13
    Much appreciated...

    Tim, you have been very generous with your time and knowledge. Thanks. I also saw this thread on the forums (you were the OP) which had lots of good info.


    Take care!

    Jerry Mann
This discussion has been closed.