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Boiler w/ millivolt gas valve turned on by itself (no thermostat call for heat).

GCR
GCR Member Posts: 10
Yesterday evening in warm DC area I noticed my boiler was on. The thermostat did not show a call for heat. I removed the thermostat from the wall, this did not fix the issue. Changed the thermostat batteries, set it to call for heat in thermostat, then set it to turn off that call in thermostat. None of these steps turned off the boiler. Turning the gas valve to "pilot" turned off the boiler.

Could a short in the wiring from thermostat to gas valve cause this? That is my next area to check.

Comments

  • mattmia2
    mattmia2 Member Posts: 5,506
    Yes. Did you disconnect the thermostat wire from the valve? Look closely at the wires before you disconnect them, they could be nearly touching and decided today was the day to touch. Depending on the age and design of the valve a bad valve could cause it too.
    HomerJSmith
  • GroundUp
    GroundUp Member Posts: 1,398
    Is it a cold start boiler? Just to point out the obvious, a hot start boiler runs like a water heater and will fire anytime the internal temp drops below setpoint- no regard to the thermostat.
    mattmia2
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 11,987
    If it is hot water with a tankless coil, it could be a defective flow check bad aqua stat or wiring problem

    If it is steam it could be a bad aquastat, wiring problem.


    But from what the OP posted it sounded like a runaway boiler.
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 5,506
    if it doesn't have a tankless aquastat or some other control keeping it hot without a t-stat call and you can't find a definite cause, I would replace the valve. If the valve is firing without an electrical signal calling for heat there are several very bad things that can happen.
  • mattmia2
    mattmia2 Member Posts: 5,506
    Look for a burned or chaffed wire between the valve and the safeties as well.
  • GCR
    GCR Member Posts: 10
    Thanks for all the helpful comments. Disconnecting the thermostat wire at the valve fixed it. Testing confirmed a short in that wire. Will replace.
    GGrossmattmia2
  • 109A_5
    109A_5 Member Posts: 122
    When replacing the old wire, inspect for damage, so maybe it happening again can be permanently be avoided. Since then the original failure is understood.
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,180
    edited June 25
    GCR said:

    Thanks for all the helpful comments. Disconnecting the thermostat wire at the valve fixed it. Testing confirmed a short in that wire. Will replace.

    I understand what you mean by "Short in the wire" however that is the incorrect term for the condition. A short circuit is when you have a conductor that connects the positive end of a battery to the negative end of a battery without a load. In AC house current is would be like placing a paperclip in a power outlet connecting the source to the return path (the white and black wire) with no load.

    On your Millivolt gas valve circuit, there is very little current and therefor no fire hazard from overheating electricity in the event of an actual short circuit. The powerpile generator may fail if shorted out. In your case there is no short. Just a bad wire that is connected somewhere, where it should not be connected.

    The correct term for your condition is a completed circuit. If a thermostat wire has insulation that is compromised (a staple or nail for example) and completes the circuit before the thermostat switch contacts, there is no short circuit. Here is a simple illustration.
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • mattmia2
    mattmia2 Member Posts: 5,506
    edited June 25
    A short is any unintended connection between 2 parts of a circuit. Many times people incorrectly call an open circuit a "short".

    https://en.wikipedia.org/wiki/Short_circuit

    In this case it is forcing the 2 nodes at the thermostat to be at the same potential even when the thermostat is open.
  • 109A_5
    109A_5 Member Posts: 122
    OK I can't help myself here.

    I agree with @GCR and @mattmia2 that a 'Short' or 'Short Circuit' is usually an undesired defect in a circuit causing unintentional results by current flowing in an unintended path or at an unintended time or both.

    A 'completed circuit' could be a 'Short Circuit' in the strictest sense. However, it looks like the common usage of 'completed circuit' is with the case that the circuit is functionally normal with no defects and it is simply in the energized state or 'On'.

    An 'Open Circuit' can be normal state when a circuit's control device is in the state that de-energizes the circuit so that no current is flowing and the circuit is considered 'Off'.

    An 'Open Circuit' can also be a defective in a circuit that when the control device is commanded 'Closed' or 'On' and the circuit does not function as expected due to no current flow caused by the defect.

    Open and Closed have the exact opposite definitions in the Plumbing world as compared to the Electrical world.

    Examples:

    A 'Closed' Plumbing valve stops the water from flowing.
    A 'Closed' switch allows the electrical current to flow.

    An 'Open' Plumbing valve lets the water flow.
    An 'Open' switch stops the electrical current flow.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Dave Carpentier
    Dave Carpentier Member Posts: 169
    I always thought of a "short circuit" as just that.. a shortened path. The electricity couldnt get to where it needed to go, it did a u-turn and went back home. (lol)
    In telecom wires, we used terms like dead-short and partial-short. A partial short is a high resistance connection between the wires due to water ingress or some physical damage (many times due to birds trying to peck the wires for nesting). An intermittent-short would randomly dial numbers (via pulse dialing).
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
    EdTheHeaterManmattmia2
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,180

    I'm sorry @109A_5 but I must disagree with the statement that the initial problem mentioned in this discussion is in no way a short of any kind, Dead Short, Partial Short, or even a pair of Short-Shorts.
    mattmia2 said:

    A short is any unintended connection between 2 parts of a circuit. Many times people incorrectly call an open circuit a "short".

    https://en.wikipedia.org/wiki/Short_circuit

    In this case it is forcing the 2 nodes at the thermostat to be at the same potential even when the thermostat is open.

    There is only 1/2 of the definition of a short circuit in the given problem mentioned above. Therefore it is not technically a short.

    The 1/2 that is missing is the part that states "....with no or very low electrical impedance. This results in an excessive current flowing through the circuit."

    Since the gas valve is included in the circuit, the normal impedance of the circuit is present, operating the gas valve, although not the intended operation, but also not a Short circuit, since there is no "excessive current flowing".

    When your are right, you are right. An I'm Right, and I know it. :p

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • Jamie Hall
    Jamie Hall Member Posts: 18,909
    Being slightly perverse... I wonder if the original use of the term "short circuit" may not derive from telegraphy (what's a telegraph, grampa?). There, a short circuit was quite literally that: somewhere along the line between East Overshoe and Smith Station there was a defect in the wire which allowed the signal to be cutoff beyond it (in either direction) but which appeared more or less normal at each end. It wasn't an open -- that was obvious enough -- but it allowed current to flow, it just never made it to the receiving set at the other end. I doubt that the distinction between high impedance shorts and low impedance ones ever mattered, since telegraphy was inherently remarkably high impedance anyway (10 miles of iron wire will do that to you...). And it usually wasn't a matter of crossed wires, either (that gave a variety of very strange problems!), since most telegraphy was earth return.

    Just speculating.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • 109A_5
    109A_5 Member Posts: 122

    When your are right, you are right. An I'm Right, and I know it.

    @EdTheHeaterMan Clearly you don't understand. You are wrong and sadly don't know it.

    Go back and read or re-read the link that @mattmia2 provided.

    In the case of @GCR the DESIRED current is 0.000000000 Amps, Zero, No current flow, No electrons moving. Because of the defect, the 'Shorted Circuit', the control device (the thermostat) is rendered inoperative (from a system point of view) and the circuit has excessive current since ANY current above 0.000000000 Amps is 'excessive' as compared to the desired state of 'Off or an 'Open Switch', No current flowing, None, Zero, 0.000000000 Amps.

    In this case it is not about the impedance of the Gas Valve or the impedance of the AC power source, it is about the impedance of the control device, which the desired state was 'Open' or 'Off', an infinite impedance. Since the 'Short' in this case is with the wires going to the thermostat the low impedance 'Short' is commanding the Gas valve to the undesired active state causing the burner to be active in @GCR's case.

    No where does it define the the low impedance path HAS to be directly across the power source. Just between two nodes of an electric circuit intended to be at different voltages, an 'Open Switch' in this case.

    The shorted battery terminals is ONE possible example BUT NOT the only example. You need to better understand Thévenin equivalent resistance.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,180
    edited 7:54AM
    @109A_5
    You clearly don't understand whet the words are saying in the link that @mattmia2 posted. here is the first and most important section of the link
    "A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit. The opposite of a short circuit is an "open circuit", which is an infinite resistance between two nodes.

    In you followup of that post you selected the portion that any good politician would use. the part that reinforces your position. A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current.
    to travel along an unintended path


    The part that of the definition that proves my fact is with no or very low electrical impedance. This results in an excessive current flowing through the circuit.

    In your infinite wisdom can your explain "with no or very low electrical impedance. This results in an excessive current flowing through the circuit" to me? If you believe the unintended path thru the gas valve's solenoid windings is a path with no or low impedance, then you need to read more books on electricity. Just read the remainder of that Wikipedia article. there it mentions over heating, fire, explosion, damage, and all other unwanted scenarios. They also mention that some short circuits are intentional, as in welding, or perhaps the "crowbar circuit protectors."

    If this were to happen on a 24 volt or a 120, 220 or 440 volt circuit, the result would be the same. The operation of load (with the related impedance of the load) when otherwise unwanted. If that same defect in the wire happened between the source and the return path without the load, then it would be a short circuit. The same piece of wire in one location IS a short and in another location IS NOT a short. So don't get your shorts in a bunch and sit back and learn something!

    @GCR's bad wire is completing a circuit, it is not a short!
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • 109A_5
    109A_5 Member Posts: 122
    @EdTheHeaterMan, Go back and read or re-read the link that @mattmia2 provided. It is you that needs the education. Maybe it will sink in, it is simple. @GCR did not want want his boiler running. The desired circuit current in this case IS NONE, ANYTHING BEYOND NONE is EXCESSIVE !!!!!!!!!!!!

    AGAIN !!!!!!!!!!!! In this case it is not about the impedance of the Gas Valve or the impedance of the AC power source, it is about the impedance of the control device, which the desired state was 'Open' or 'Off', an infinite impedance. Since the wires to the control device are 'Shorted' there is a low impedance path bypassing the control device. A SHORT CIRCUIT !!!

    Talk about a good politician, YOU clearly do not understand the Whole of the article that @mattmia2 posted, you probably never will, because you are stuck on an ill conceived theory that does not hold weight in the real world, no wonder folks have such a hard time understanding Electricity with nonsense like this being spewed.

    If that same defect in the wire happened between the source and the return path without the load, then it would be a short circuit. @GCR's bad wire is completing a circuit, it is not a short!

    Again, your amazingly limited definition of Short Circuit is ONLY ONE example, @GCR's bad wire is completing a circuit, is another, like it or not, It is a short circuit !!!

    "A short circuit is an abnormal connection between two nodes of an electric circuit intended to be at different voltages." You seem to conveniently IGNORE the FACT that the two nodes DO NOT have to be across the power source. The author's intentionally used the words "two nodes" to avoid nonsense like yours.

    When the thermostat is 'Open' or 'Off' there is different Voltages on each terminal. With the thermostat wires 'Shorted' that is no longer true, it is a 'Short Circuit'.

    Without looking it up can you define "Impedance" as it applies to an Electrical circuit ??? I can.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Jamie Hall
    Jamie Hall Member Posts: 18,909
    @109A_5 . May I respectfully submit that your tone, if not your content, is out of line with the custom of the Wall.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England