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Please help diagnose gas steam boiler issue!

jlggomez Member Posts: 2
Hello, new to the forum and thanks in advance.

I have a Burham gas steam boiler that has been working inconsistently and I would greatly appreciate any trouble shooting help and suggestions. The issue:

The boiler has been working just fine for several years, until a couple of months ago when it started acting up. It will be working as expected, cycling on/off correctly according to the thermostat setting and providing great steam heat to my house radiators. Then, unexpectedly, it will simply stop working and won’t come on even though the ambient temp dips below the thermostat setting. It will stay asleep for an hour or longer with the ambient temp continuing to fall further from the thermostat setting and then it will decide to come on and function as normal for maybe several hours to a day or so; and then the same thing will happen. Thinking that the issue is the thermostat, I replaced the Honeywell thermostat with a new unit (same model), but the same thing happens. I have checked the voltage that the thermostat is “seeing” and it mostly hovers right around 20V AC +/- .5 Volt. However, on occasion, I have measured voltages as low as 18V. Honeywell tells me that the thermostat needs to see 20V. However, the heat will often come on and things work as they should during those times that the voltage dips below 20V; but other times it won’t.

What would be the most likely cause of this problem? If the thermostat needs to see 20V, why would the heat work many times when the voltage does dip below 20V? What would be the cause of the variability in the voltage and is this the cause of the problem? Any tips/suggestions are greatly appreciated. I am pretty handy and am aware of safety concerns when working with electrical equipment.

Thank you!



  • Jamie Hall
    Jamie Hall Member Posts: 23,318
    Very first thing I would check is to see if the pressure control can actually see the boiler pressure -- is the pigtail completely clear? the opening into the boiler?

    Next thing would be the low water cutoff -- if it's the float type, has it been blown down regularly? Is the float really free to drop and rise as needed?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,062
    There are several devices that can cycle your boiler.
    Your tstat is just the first in series with those other items.

    Can you post pictures of your boiler from floor to ceiling showing piping and any controls you see?
  • jlggomez
    jlggomez Member Posts: 2
    Thank you both for your responses; it is appreciated. I will do as you suggest and report back. Thanks again.
  • mattmia2
    mattmia2 Member Posts: 9,660
    If no one has looked at it in several years, someone that understands steam really should go over it and test all the safeties as well as figure out your intermittent problem.