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  1. #14
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    Jul 2012
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    WA
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    So this is a site with lots of unit heaters and only five have problems. These five are in different buildings. The problem is not common to them all. One possibility is they failed one at a time and no one complained for a while until a bunch had failed. One other thought is the original thermocouples were bad. When they were replaced they were over tightened, damaging the gas valve. Some gas valves are more sensitive to over tightening than others. I was taught to never screw in a thermocouple more than 1/4 turn past hand tight.

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  3. #15
    Join Date
    Nov 2006
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    Southeastern Pa
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    It will be interesting to see what the problem turns out to be.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist
    Member, IAEI

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  5. #16
    Join Date
    Jan 2010
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    I say replace a valve on one and go from there.

  6. #17
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    Feb 2004
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    New Mexico
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    I wouldn't replace anything yet. You have the adapter. A t'couple can't be properly tested w/o a load. Like a battery, the condition needs to be load tested. The test is two parts. The first with no load then with connected to the solenoid engaged. If the adapter didn't come with any charts you can probably find one an Honeywell. It shows the pull in/drop out graph where the t'couple should function.
    But I don't think the pilot sensing is your problem. Hook up your adapter, lite the pilot and watch the readings when the burner is fired. It should remain within the range on the graph. If you don't have a graph you should not drop out. Most are OK at 8 mv.under load. A gas line with too much pressure drop is often the problem as you have 5 with the same problem I would suspect pressure drop.
    Exhaust fans that bring in some of the make up air from the flues can create these problems by drawing the flame away from the t'couple.
    The thing is, watch the flame to find if the problem is the pilot flame drawing back from the spot it needs to hit. That spot is 1/2-3/8 inch at the top of the t'couple. If the flame is too low the t'couple won't generate what's needed and will also fail soon.
    My 2 cents.

    I also will tell of pilot outages where some one, out of frustration probably, increased the pilot orifice hole to try to keep the pilot from going out w/o fixing the actual problem. This will burn out the t'couple fairly soon.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

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  8. #18
    Join Date
    Jul 2010
    Location
    US of A
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    Quote Originally Posted by Red Man View Post
    So this is a site with lots of unit heaters and only five have problems. These five are in different buildings. The problem is not common to them all. One possibility is they failed one at a time and no one complained for a while until a bunch had failed. One other thought is the original thermocouples were bad. When they were replaced they were over tightened, damaging the gas valve. Some gas valves are more sensitive to over tightening than others. I was taught to never screw in a thermocouple more than 1/4 turn past hand tight.
    I have seen this many times. The call only comes in when enough people compalin and they can't keep up with the load.
    Signature removed Violated rule #15

  9. #19
    Join Date
    Jul 2019
    Location
    Oklahoma home its in the name
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    I have a solenoid from an old carier 60% gas valve i think it was. I just screw the thermocouple into it and if it holds then i call the valve bad.

    Sent in a state of increasing entropy using Tapatalk

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  11. #20
    Join Date
    Mar 2018
    Location
    Sumter, SC
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    Thread Starter
    I am hoping to get back to that site tomorrow. I am fortunate that my boss isn't a jerk and knows that I am a rookie tech. He has called a local company that is owned by a former HVAC instructor at the college where I work to come and look at the units. My boss asked him and he agreed to let me be there to see what a seasoned tech finds wrong with the units. At least this way I can learn something for next time.

  12. #21
    Join Date
    Jan 2010
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    Quote Originally Posted by Fender60 View Post
    I am hoping to get back to that site tomorrow. I am fortunate that my boss isn't a jerk and knows that I am a rookie tech. He has called a local company that is owned by a former HVAC instructor at the college where I work to come and look at the units. My boss asked him and he agreed to let me be there to see what a seasoned tech finds wrong with the units. At least this way I can learn something for next time.
    .
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  13. #22
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    Mar 2018
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    Sumter, SC
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    Thread Starter
    Well things did not go according to plan. I was called out to another job and the outside company went and did some troubleshooting. What they came back with is bad gas valves. The boss told them to change one and see if their theory was correct and if it is, then I will change the rest. If not, then back to square one.

    I know it is unlikely that five valves went bad at the same time. What is possible is the site has been neglected for numerous years and the valves all didn't actually go bad at one time. Previous tech was fired for goofing off instead of working. It got so bad they put a GPS tracker on his truck and found him 45 miles away from where he was supposed to be at.

  14. #23
    Join Date
    Oct 2009
    Location
    Atlanta,Ga.
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    Take the magnet out of a good gas valve(When you discard an old valve or furnace) Use the old magnet as a service tool.Take the thermocouple out of the gas valve you are working on.Screw the thermocouple into the Magnet(Tester).Lite pilot hold in the magnet.See if it holds in!!!If it holds in,Thermocouple is good.May have a bad valve.Make sure you don't have an ECO.Look for 2 wires coming out of the gas valve, going to a temp switch or fusible link.An ECO will break the thermocouple MV signal,If it is open,Preventing pilot from staying lit.

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  16. #24
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    Sep 2018
    Location
    Summerville SC
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    If these are all old units , and or they don’t have drip legs in the gas line, the pilot safety valves maybe corroded or seized up. Try tapping on the gas valve before you release the pilot knob to free them up . Worked for me numerous times.
    If that doesn’t work and you have 30 mv with no circuit Wires under the thermocouple, you need new gas valves.

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  18. #25
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    Sep 2018
    Location
    Summerville SC
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    Also to note , you must have a strong blue pilot flame hitting the thermocouple tip, no lazy red flame.

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  20. #26
    Join Date
    Feb 2004
    Location
    New Mexico
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    First observe then fix.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

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