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  1. #1

    Fireplace Problem

    Hey Guys Im looking for advice on a Fireplace problem. this fireplace has a simple flip switch with 2 wires connecting to TH &TH/TP.
    During my inspection, I found the thermopile to be faulty since it was only making 60mv. I replaced the Thermopile and now im getting good millivolts (around 650+mv)

    The problem is that even after replacing the thermopile, it still does not open main gas valve. The thermocouple will hold the pilot fine, so I dont think its the thermocouple and the thermopile is brand new. also when checking the MV on the thermopile, when the flip switch is closed, The MV would go up to around 650MV but than after "OL"

    Could this be a problem with the Gas Valve now?

    I tried to jump out the switch but still will not light main burners

    Thanks for the advice everyone

  2. #2

    Lennox Fireplace MV Wont open

    Hey Guys Im looking for advice on a Fireplace problem. this fireplace has a simple flip switch with 2 wires connecting to TH &TH/TP.
    During my inspection, I found the thermopile to be faulty since it was only making 60mv. I replaced the Thermopile and now im getting good millivolts (around 650+mv)

    The problem is that even after replacing the thermopile, it still does not open main gas valve. The thermocouple will hold the pilot fine, so I dont think its the thermocouple and the thermopile is brand new. also when checking the MV on the thermopile, when the flip switch is closed, The MV would go up to around 650MV but than after reads "OL"

    Could this be a problem with the Gas Valve now?

    I tried to jump out the switch but still will not open main burners

    Thanks for the advice everyone

  3. #3
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,197
    Rockstar, this is not a DIY advise site. You can get your post count up and apply for Pro status where we have forums in which we can discuss technical details including troubleshooting in detail. I think I can say you need to check your switch leg. 650mv would be a good open circuit mv reading but you should never see open line. If you are not an HVAC service tech but homeowner, call a hearth pro. Don't blow yourself up.

  4. #4
    Join Date
    Dec 2011
    Location
    Northwest Georgia
    Posts
    111
    Have you checked your gas pressure?

  5. #5
    Gas pressure is ok. I'm just wondering why it goes open loop when I check the thermopile. It climbs up to about 650mv than goes open loop. I'm thinking it could be a short in the gas valve but I'm not sure. I don't really work on fireplaces but more on furnaces

  6. #6
    Join Date
    Apr 2004
    Location
    MN
    Posts
    1,803
    Silly question, but is your meter capable of reading above 650 mv? Also, did you clean the wire connections at the valve? Doesn't take much resistance to stop the flow of current when it's that small.
    A Veteran is a person, who at some point in their life, wrote a blank check payable to the United States of America for payment up to and including their life.
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  7. #7
    Im using the Fluke 116 and It says that the range is 600MV so im guessing thats the reason why im getting the open loop. Wire connections are good, no rust or dirt on them.

  8. #8
    Join Date
    Dec 2011
    Location
    Twin Cities Minnesota
    Posts
    240
    Do you have wiring diagram ? Many of those things had a "hi limit' switch hiding in the circuit !

  9. #9
    Join Date
    Mar 2001
    Posts
    1,491
    Invest in a millivolt tester that will also power the gas valve. I have two. One is a Honeywell w720 system tester, and the other is an Annie thermocouple analyzer. You test the generator or thermocouple, then power the gas valve thru the meter, slowly lower the output millivoltage to the point where the gas valve closes, that tells you what the valve require in millivolts to hold in. Testing the generator-thermocouple will show you what the output millivoltage is. Had my Honeywell for 43 years. Bought the Annie in 1982.
    One way to outthink people is to make them think you think. They'll think you're not really thinking what you're trying to get them to think you think...........

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,125
    Merged your threads. Please don't make duplicate threads, thank you.
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    How many times must one fix something before it is fixed?

  11. #11
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,197
    If you have all the leads removed from the valve with just the TP connected and when you jump out TH to TP/TH and get Open Line, the valve is bad.

    Fluke 116 is great for DC millivolts.

    Note that testing a TP disconnected using alligator clips for an open circuit test only indicates the potential power output. It does not show its performance under load, which is what your closed voltage reading is.

    TC and TP are unrelated in functions when you have both on a valve except the main operator relies on the TC to hold the EPU open.

    HTH

  12. #12
    Cosmicmuffin: I checked the wiring diagram and found there is a limit. But I traced the wire and it looks like it just comes from the switch to the valve. Also looked up In the vent and found no hi limit. Plus I jumped the valve from TH to TH/TP and it still would not start.

    Uniservice: I'll look for one at the suppliers. I'm just a new tech so I won't have all the special tools yet.

    Hearthman: I'll give that a try. I'll be going over the customers place over the wknd to check that out. I had all the wires connected when trying to jump the fireplace. So should I just remove the TH and TH/TP wires coming from the wall switch than test? I checked the range for the fluke 116 and the range says 600mv could that be the reason why I get open line as well?

  13. #13
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,197
    Again, the Fluke 116 is one of the best meters available for reading DC millivolts so it isn't the meter. However, if it makes you feel any better you can go to Radio Shack and get their cheapest digital DMM for under $30 and it will read DC millivolts just fine and it is autoranging.

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