Oil Boiler Problem

Discussion in 'Boiler Forum' started by Timmons, Jul 23, 2014.

  1. Timmons

    Timmons New Member

    Messages:
    3
    Hello,

    I'm having a problem with my oil boiler. Upon returning from vacation recently I came home to the water being completely drained out of the valve. Upon refilling it as my system is manual fill, the boiler started and the heat came on. The thermostat is an automatic timing one where I had the heat turned off. No matter what I did with the thermostat the heat remained on and the boiler would not stop. I called a technician and he proceeded to unplug the wires declaring they were old and need to be replaced and that a plumber part like a spark plug was needed for a cut off valve as it was not functioning. They then changed their story that the whole system was bad and needed to be replaced. I reconnected the wires and the boiler does start up immediately. Does anyone have any suggestions on what this could be? The tech said the boiler itself was fine and it seems to be either this plumbing part or wires.. yet with power being supplied why would the wires need to be replaced?

    https://picasaweb.google.com/1138665...K7J0Ky-jo6ilQE

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  2. Reach4

    Reach4 Active Member

    Messages:
    2,251
    Location:
    IL
    The wires that he unplugged-- where are those wires? Are they the wires that are at the thermostat or the wires that go to the thermostat? If you probe around the disconnected connector with a multimeter set to AC volts, what is the highest voltage that you can find?

    I suggest that you post a photo of the spark plug looking thing. I won't know what it is, but somebody else probably will.

    Was your technician from a big company?

    I don't know about these systems, but I think you are wise to be cautious. Be glad that you have time to check things out.
  3. Dana

    Dana In the trades

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    The McDonnell N-47-2 in the pictures is the automatic water level control (I assume this is a steam boiler, and not pumped hot water?). There is no failure mode of that unit that would keep the boiler firing without a call for heat from the thermostat, but it's supposed to suppress firing if the water level drops too low (and hopefully it worked, thus saving the boiler and the house.)

    The important things to figure out are why the boiler ran dry, and why it's heating the house when the thermostat isn't calling for heat.

    There are a couple of possible innocuous explanations for why it would fire up upon refilling though.

    If the boiler is also used for heating your potable hot water it's normal for it to fire until it reaches the setpoint of an aquastat setting for the hot water coil, but that aquastat should have a high-limit well below steam temperatures. If you're not heating hot water with it you can just turn it off for the summer, as there is likely to be a min-temp aquastat keeping the boiler at a high temperature (below the steam heating temp) to keep the delay time between the call for heat and the production of steam short.
  4. Timmons

    Timmons New Member

    Messages:
    3
    Hello,
    Yes there is an aquastat and it is used for hot water during the summer as well. What would cause it to reach the aquastat temperature but keep going and produce steam? Can aquastats go bad? I've had 2 guys over (from the same company) and neither mentioned what you did. The water level did go too low and it stopped, we were away on vacation and weren't there to fill it. Now I know to just shut it completely off during the summer when we are not there to cycle the water. Its the first year in this house and understanding all of this wasn't something I anticipated.

    And another thing.. the guy unconnected the wire and the aquastat and boiler is making hot water without issue now. We are just concerned about how it will perform when its heating season again. Gotta figure out who should be able to fix this? plumber/electrician or the oil delivery/boiler company.
    Last edited: Jul 23, 2014
  5. Timmons

    Timmons New Member

    Messages:
    3
    The wires are those that go to the thermostat in the boiler room. I dont' have a multimeter. What's a good one to get? The tech was from an oil delivery and boiler maintenance company.
  6. Reach4

    Reach4 Active Member

    Messages:
    2,251
    Location:
    IL
    Go with what Dana says.

    A multi-meter is handy to have anyway. As an occasional user, you could use a cheap one. Just be gentle with the test leads. I plugged multimeter into the Walmart site and found the first one in the list costs $7.88.

    For somebody who uses this as a professional tool, I would go Fluke.
  7. Tom Sawyer

    Tom Sawyer In the Trades

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    Location:
    Maine
    Te problem is either the thermostat or the primary control. Possibly the aquastat for hot water but unlikely.
  8. Dana

    Dana In the trades

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    If the boiler has a model number, there may be a manual & schematic available online, which would make sorting this out a bit easier.

    BTW: The standby losses of steam boilers are pretty high, making it's average efficiency at low load (such as only heating domestic hot water) pretty low. With an embedded tankess coil the idling temperature of the boiler typically has to be over 160F to provide reasonable hot water performance, which increases the standby losses compared to a boiler that can be cold-fired (allowed to cool to room temp) or a boiler maintained at 140F at the low side, and serving an indirect fired tank. Oil is an expensive fuel on a per-BTU basis, and in most places it's cheaper to heat hot water with a plain old electric tank type hot water heater during the summer & shoulder seasons than with an oil fired boiler, at recent years' oil pricing. In lower cost electricity locations it can be cheaper even during the coldest months of the year. It's pretty common to burn $300-500 worth of oil during the summer season when the only load the boiler is serving is the hot water.
    Last edited: Jul 24, 2014
  9. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
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    Location:
    Maine
    Makes no difference who makes the boiler. It's oil fired so there is a primary control that opearates the oil burner. The thermostat low voltage wires run from the thermostat to the TT terminals on the primary control. The AC power to the primary control breaks through the pressure trol and the low water cutoff, wired in series. The hot water aquastat also wires to TT on the primary control. If the burner fails to shut off it can only be either the thermostat, aquastat or the primary control itself. If the boiler runs out of water, the float on the low water cut off drops and breaks the Ac voltage to the burner. The pressure-trol could also cause the problem if the tube running from the boiler to the control gets plugged with sediment. Something that should be checked once a year.
  10. Dana

    Dana In the trades

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    Yabbut, most people find it easier to follow a printed schematic than a verbal one, eh? ;-)

    Controls on steam boilers are about as dumb as a box o' rocks, dead simple to debug once you understand it, but Timmons is clearly a newbie.
  11. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
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    Location:
    Maine
    I keep things like that purposely vague. Although steam controls are indeed simple, a steam boiler is likely the most dangerous of all systems and not something that should be toyed with by amateurs.
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