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old National boiler

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Flashv208
Flashv208 Member Posts: 2
in Strictly Steam

I have an old boiler. National US Radiator 0-4GW. Looking for manual or drawing to show location of flame sensor. I see one for the pilot flame, but can't locate sensor for main burner flame.

The pilot stays lit, circulating pump is running, main flame shuts off before reaching set temp.

Comments

  • 109A_5
    109A_5 Member Posts: 3,684

    How old is it ? Pretty old I bet. It may not have a flame sensor like a newer boiler would.

    Something in the electrical control may be shutting the burner off.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • mattmia2
    mattmia2 Member Posts: 15,984
    edited January 25

    typical gas trains just prove the pilot flame and if the pilot flame is proven turn on the main burner. if it is a total shutoff system it will turn off the gas to the pilot if it doesn't prove the pilot. if it is an older wild pilot system the pilot burner is controlled with a manual valve and it only proves pilot to control the main valve.

    can you post some pictures of the gas train?

    it could be shutting off on high limit on the aquastat or it could be a problem with proving the flame. if the main valve is opening for part of the cycle it is more likely that some other safety is shutting off the main burner valve although it is possible that whatever proves flame(thermocouple, thermopile, mercury switch, thermostatic switch) is intermittent.

  • HVACNUT
    HVACNUT Member Posts: 7,305

    How long does the main flame stay on?

    Whats the limit setting, and at what temperature is it shutting off?

    Are you sure the temperature gauge is correct?

    Are there 2 aquastats (high and low)?

    Is there a tankless coil?

  • Captain Who
    Captain Who Member Posts: 563

    So, do older boilers such as this have no blocked vent switch in addition to no spill switch?

  • Steamhead
    Steamhead Member Posts: 18,319
    https://forum.heatinghelp.com/discussion/comment/1884022#Comment_1884022

    In most cases, yes. I don't think these became standard on residential boilers until at least the late 1980s.

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • 4GenPlumber
    4GenPlumber Member Posts: 16

    Nationals used to have Baso Switches. The pilot stayed lit, but the baso wouldnt allow the main burner to fire. If it has a Baso switch, reset it. If that doesnt work, replace the thermocouple and try again.

  • Flashv208
    Flashv208 Member Posts: 2

    so is it a thermocouple or a flame sensor. it is mounted right in front of the pilot flame. sometimes if it didn't turn on main burner, it would if i held a flame to the other side of it. I also removed and tried to clean it. I read they would get a build up of carbon or soot. It does not have a wire attached to it but rather a thin metal flexible tubing

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