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Mills 350 Steam Boiler

The pressure gauge reads 0 oz. and negative when the condensate tank is filling. The condensate tank nearly emptys in 24 hours when the supply valve is turned off. The oil burner turns on for 2 minutes and then shuts off. Steam comes out the condensate tank overflow pipe.

What does that tell you?



  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    steam in the condensate tank

    i believe you posted this problem earlier, and that you said some traps were to have been replaced in connection with the steam in the condensate tank. was this work ever done, and if so, what was the result. these condensate tanks should not have steam in them, and neither should the boiler run out of water. is there any sign of a leak? this can be checked [for internal leaks] by over-filling the boiler, and looking inside the boiler for water, or by checking the chimney on a cold day, while firing, for excessive amounts of white vapor from the chimney. buried returns can also be a source of leaking, and sometimes are hard to find.

    i presume this condensate tank is the insensitive kind that fills the boiler when a float rises inside, indicating the tank is full, which i do not like. my own boiler [1-pipe steam, 1,050,000 btu] is completely gravity return, and has no auto-fill of any kind, and instead relies on a reservoir tank. of course i live here and can check the water level and flush the lwco every few days. i don't have a meter on the make-up water feed, but i am sure that i have not put more than a few gallons in during the winter.

    i also did not completely answer your last question about system pressure. the low-pressure gauge i would choose is from gaugestore.com-0-3 psi [if equipped with a vaporstat, then 0-15 ounces]. as you have 3 pressuretrols on the boiler, i believe you have a modulating burner setup, controlled by pressure. i would recommend this modulating burner be fitted with a vaporstat to switch from high-fire to low-fire at a pressure of say 8 ounces, for economy. the original 0-30 psi gauge [unfortunately useless for diagnosing steam pressure problems] must remain for code purposes.

    did you ever find a good local steam man?--nbc
  • RogerDodger
    RogerDodger Member Posts: 4
    Return Leaks?

    Yes, the three main steam traps were replaced, but I have noticed steam coming out of the overflow pipe a couple of times. There are many ancient traps in the system that haven't been maintained.

    We replaced the gauge 0-30psi with 0-15oz. Today it was 2 oz. pressure.

    I suspect that returns that are buried under a concrete floor, are a source of leaks.

    I had Carl Tonucci, Jr. of Cordone & Tonucci Plumbing & Heating of New Haven diagnose the system. He said that zone valves were the enemy and shouldn't be used on a steam system. He recommended changing the new construction to hot water with a separate gas furnace. He would keep the church steam, heated by a smaller gas or oil fired boiler. But, leaking returns would throw a monkey wrench into that plan.

    Who do you recommend as a good local steam man?



  • Steamhead
    Steamhead Member Posts: 16,725
    edited March 2010
    Zone valves can work on steam

    if done right.

    First, you must run the pressure low. Whatever was at the end of the steam mains before, it's now a "B" dimension since the closed ZV eliminates any leftover steam pressure.

    Second, you may need to install a bleeder across the ZV so some steam pressure can bypass it, if you have trouble with water backing up into the steam pipe when the ZV is off.

    Third, if the boiler maintains pressure all the time waiting for a ZV to open, you're wasting a LOT of fuel. Rewire the controls so they can start and stop the burner as the ZVs open or close.

    Fourth, with ZVs the steam demand will vary depending on how many ZVs are open. Use a full-modulation burner, or at least a lo-hi-lo one, to avoid short-cycling and other issues.

    Last but not least, unless the "new building" is already hot-water fed by a steam-to-water heat exchanger, you're better off keeping it steam.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
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