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  1. #1
    Join Date
    Nov 2010
    Location
    indiana
    Posts
    19

    why did the flame rod replace the thermocouple?

    I believe that preventative maintenance for a flame rod involves cleaning it so anything on the surface does not insulate it causing a low microamp signal which would cut off power to the burners and a no heat situation if the flame is not sensed whether it is there or not.
    I am not terribly familiar with thermocouples and the benefits and drawbacks of their usage for flame proving.
    I believe that preventative maintenance for a thermocouple would involve checking its location in the flame and abilty to prove the flame through millivolts.
    It seems as though the flame rod requires more consistent maintenance to work properly.
    Why are thermocouples no longer used in furnaces?
    I appreciate any insight.

  2. #2
    Join Date
    Jan 2008
    Posts
    2,118
    A flame rod reacts instantly with a micro amp signal. Thermo-couple has a warm up time.
    "Hey Lama, hey, how about a little something, you know, for the effort." And he says, "there won't be any money, but when you die, on your deathbed, you will receive total consciousness." So I got that goin' for me, which is nice. - Carl Spackler

  3. #3
    Join Date
    Jan 2013
    Location
    NC/VA
    Posts
    85
    Also in respect to the flame rods safety function, it allows the gas valve to close immediately when no flame is detected. The flame creates the circuit to the power head in the gas valve. (pulsating DC Micro-amps) no flame after a short amount of time, the valve closes.
    acts as a flame proving device as well as a 100% safety device
    soot buildup on the device can affect its funcionality

    Thermocouple when the flame goes out, it takes time to cool down the thermocouple thus decrease in voltage slowly to power head while it cools down. The flame rod is quicker to react thus safer.

    yeah I guess I trying to say same thing as 2old2rock said, HAHAHA
    Travel and work,

  4. #4
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,760
    Flame rods shouldn't need maintenance in a properly tuned furnace. It's mainly IMO the by products of incomplete combustion and/or furnace condensate problems that cause flame rectifiers to get weak/insulated with soot or get corrosion on them from high humidity.

  5. #5
    Join Date
    Dec 2009
    Location
    maroon lazyboy
    Posts
    1,049
    Thermocouples have a shorter life, in my opinion...

  6. #6
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,642
    A thermocouple requires a standing pilot.

  7. #7
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,642
    Also, the flame rectification sensor is very often (not always) used to prove the main burner, and is typically placed at the last burner in the line, opposite the ignitor ensuring the entire train has lit off. Proving a pilot can still allow for failed or delayed ignition at one or more burners (due to dirty crossovers, plugged orifice, etc). Flame rectification is instant. The board will only flow gas for four seconds or so (usually) before shutting down on a flame failure. Thermocouples have to warm up - if you were trying to prove a main burner with a thermocouple gas would have to flow for a very long time before it could prove by seeing millivolts.

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