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Gas boiler burner flame too big/yellow

njwebdevguy Member Posts: 33

We have an American Standard gas boiler thats been a reliable heater, but I think the flame is set too high now. The air shutter adjustment doesn't make much of a difference, I think there is too much gas being sent to the burner. How can I turn it down so the flame is the normal blue with just a tiny bit of yellow? The control is a Robertshaw control, it looks like the Millivolt models on their web site.

Thank you


  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    You need two things to do this adjustment.

    A combustion analyzer and the training on how to use it. I understand you are handy, and I am sure know way more than I ever will about what you do for a living. I am saying for family health and safety get a pro in to test and adjust this thing properly. It is not eye ball it and turn a screw.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • njwebdevguy
    njwebdevguy Member Posts: 33
    I had to do something

    I can't believe it was adjusted so high. They were at least six inches high and yellow. I turned it down so that the burner flames are now maybe an inch and a half high and 97% blue. I took a before and after pic, I need to charge my camera battery up and then I will upload them.

    I think the cost of a person coming to check the boiler will be more reasonable price wise than asking somebody to fix an unknown problem.

    The boiler is a 1967 boiler, its very old. I wouldn't mind replacing it when I can afford to. But if its not absolutely necessary, I can't justify it. We spend very little on heating as it is now, we have triple paned windows and we've done a fair amount of insulating in the important places. The house is small and almost perfectly square. Not a lot of surface area.

    The adjustment I made was the other adjustment on the robertshaw, immediately to the right of the pilot knob. Under the cover, with a screwdriver.

    Is that safe? I remember reading that it was the gas pressure adjustment and obviously the gas pressure was set too high.
  • Empire_2
    Empire_2 Member Posts: 2,343
    When lasty serviced?

    If it has not been services in a while, I would guess that the furnace needs to be cleaned.  Over time debrise and the by products of combustion needs to be cleaned.  This is a job for the professional. 
  • njwebdevguy
    njwebdevguy Member Posts: 33
    Photos attached

    It was cleaned last year - but while he was there the repair guy (from the gas company's service contract program) turned it way up.

    The flames were more than six inches tall and yellow and it was also noisy..

    More recently we had a different, independent repair guy - who seems straightforward - over and he replaced the shutoff valve, but didn't (wouldn't) adjust the flames.

    Its an old unit.

    1967, the sticker on the front says..

    I'm attaching the before pic of how it had been adjusted last year, taken today..

    You can't really see that well how high it had been set.. It was very high

    The second pic is the after.. now.. Its much lower. I actually turned it up a tiny bit after the second pic was taken.

    The bottom line is that I dont want to be wasting gas and shortening the remaining life in the unit.

    I had to do something. With the flame turned way up like that it didn't look safe.

    Question: is it set too LOW in the second pic?
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Per Charlie...

    You really can not adjust by eye. A combustion analyzer must be used.

    As for firing rate, go to the gas meter with a stop watch.

    Record the amount of time necessary for the fastest dial to make one full revolution. Make certain that no other appliances are on during this test. Also make note of the volume related to the fast dial.

    Using a calculator, take 3600 and divide by the elapsed time for one full revolution of the meter needle. Multiply that answer times the amount of gas per revolution (typically 5 CF for residential meter).

    Multiply that answer times the caloric BTU content per cubic foot (typically 1050 per cu.ft. near sea level.)

    The result of that answer is how many BTU's per hour you are pushing into the appliance. Check it against the manufacturers rating plate, and if greater than 10%, adjust accordingly to get it within reason. Less than rated is better than more than rated input.

    A word of caution. The old cast iron burners have a tendency to lose parent material around the holes in the face of the burners. This will cause tall flames like you were seeing. Adjusting the gas pressure downward can compound this problem, resulting in flash back (flame inside the burner) and the excess production of carbon monoxide.

    If you don't have a CO detector, GET ONE TONIGHT, and place it near your bedroom.

    Start saving your money. Your boiler has exceeded its reasonable life expectancy...


    There was an error rendering this rich post.

  • njwebdevguy
    njwebdevguy Member Posts: 33
    edited November 2011
    Thank you for that tip

    The burners are okay..They aren't cast iron. They look like steel or more probably, stainless steel, so I guess they are probably not the original equipment. The burning surface- the area with the holes also looks replaceable. there isn't any visible erosion I can see. Nicer than our gas range burners.

    We have three CO detectors, two of the battery kind and a digital one with AC power and battery backup that reads in ppm.

    We do plan to replace the boiler, soon. But I don't want to do it in a hurry without the ability to do the appropriate research on what's the best choice for us. We probably don't need as large a boiler any more. We've done a lot of insulating, we put in foam upstairs, we have new windows.. Each dramatically reduced our heat loss.

    The heater is running fine now and the house is toasty warm. I'm going to be a bit more comfortable running it at this normal flame height.

    [EDIT] I think the burner is shutting off too soon and then allowing the circulator to run a long time without flame. Maybe the aquastat is set too low. Will be looking into how to set that. [/EDIT]

    But the heater doesn't have the weird fume smell it did before.
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