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Robert Shaw 7000 Series Gas Valve Help

RS calls it a thermopile but it is a single end screw in thermocouple. I replaced it last fall and it gets to 750mv but... when all else is eliminated, that which is left must be it... I'm going to get a new thermocouple this AM. The first one was a generic but I know who has the RS ones now. I just found it hard to think the new one had failed so soon. I am going to double check the pilot aim as well to be sure it isn't getting cooked.

Comments

  • Paul Ellison
    Paul Ellison Member Posts: 16
    pilot won't stay on

    Hi Folks - You all were very helpful a few years ago when I was setting up my new WM boiler to run on my 1926 Trane Vapor system. I come to you folks again with a more modern problem. When I started the system this fall, the pilot wouldn't stay lit. Using the old water heater rule, I replaced the milivolt thermopile with a new exact replacement. Since then there have been 2 or 3 times I've had to relight the system. Tonight it won't relight. I put my digital voltmeter on the pile, after a minute or so it is at 750mv which is spec. I'm thinking the magnetic safety is shot. Any opinions? I plan to visit the local supply house for one tomorrow but I'd like to hear what the pros say. Thanks!
  • Chris_82
    Chris_82 Member Posts: 321
    For starters the 7000,...

    http://www.pitco.com/PDFs/RS7000/7000 Valve Relighting Sequence.pdf

    for starters is it one of the recalled units?
  • Paul Ellison
    Paul Ellison Member Posts: 16


    I checked the recall info last fall when this began. According to the date code, it was built before the recall period. The boiler was installed 10/02 and the recall units were built Feb 03 and later. Thanks for the relight sequence link, I followed it exactly.
  • dana_3
    dana_3 Member Posts: 57
    PILOT LIGHT

    pull the pilot tube assembly, clean the tube and pull and clean the gas orifice
  • Paul Ellison
    Paul Ellison Member Posts: 16


    Thanks Dana - did that too. I am getting 750mv from it. The magnet shows a resistance of 10 ohms - way too much, I feel. After visiting some parts houses, I called RobertShaw. They can't get the part for me either. It is a special one made for Weil-McLain. I plan to call W-M in the morning. I've been given the "nobody will sell it to you, no license" lesture several times already. Harrumpf! I'll replace the whole ding-dong valve if I have to. Grrr.
  • Chris_82
    Chris_82 Member Posts: 321


    I just don't know enough about measuring the resistance of the pilot circuit at the valve, it's one of the items missing in the pdf fax sheets. Generally if the pile is measuring that voltage, we say it's good and think about scraping the valve...on the other hand how much other circitry is in the loop, is there a thermostat and limit control in this pilot circuit as well? I had a fireplace once that had a snap type limit on the top of the unit, tested fine with an ohm meter, but I didn't notice that when I was lighting the pilot, which always made an umpfh sound the overpressure flap would open, as it should, to protect the glass etc., and the snap switch was right next to it, the flap would stick open the smalles amount, after the fireplace was put into position, the act of moving the assembly out to look once again and the flap would just go back to its normal position, confounded me repeatedly untill we jumped out a perfectly good switch, we finally ran the thing in the persons living room, not reccomended, and saw the moving and sticking flap, my point is sometimes the little things can be very frustrating and it might be something you have already looked at.
  • Paul if the resistance of the

    power unit is 10 ohms that is good. Most modern powerpile valves the magnet assembly is 10 to 11 ohms. Magnet assembly's are not feild replaceable. If it needed replaced an entire valve would be required.

    If the pilot keeps going out there may be combustion issues involved. I would suggest someone do a combustion test on the equipment.

    Try this with the pilot lit and your meter connected across TP/TP on the valve disconnect the thermostat wire, you should read around 600 to 650 if you are getting 750 millivolts from the generator. If so the magnet circuit is okay and you have a problem not related to the gas valve or millivolt circuit.

    I have a complete procedure available on how to troubleshoot powerpile systems, I will mail it to you for free. Contact me at [email protected] and give me your postal mailing address.
  • Paul Ellison
    Paul Ellison Member Posts: 16


    There is a magnet assembly replacement, according to RobertShaw. Uni-Line pt # 1750-018. This is a 7000RHC valve. The only shop that could get it so far won't sell to me. I admit I love the challange of this type of job. The pilot will only stay lit while I hold the button down so something isn't happening with the thermocouple/magnet - there is nothing else in the circuit. I may have made a confusing description about the thermocouple, the package called it a thermopile but it is the screw-in type. Dang, so much for my brilliant diagnosis. Maybe I'll get another thermocouple and see how it goes. Pilot flame is perfect, no stutter, nice & blue and hits where it is supposed to. I might have to give up and call the guy who put it in, we're supposed to get 20 degrees next week. Thanks for the help and keep it up!
  • Thermo couple tester...

  • Paul Ellison
    Paul Ellison Member Posts: 16


    Thanks for the offer, Tim. I may have just had an Ah-HA moment. I'll report back but I'm leaning toward bad thermocouple (again).
  • Paul Ellison
    Paul Ellison Member Posts: 16


    Thanks Mark, too. Your note supports my Ah-HA.
  • Arthur
    Arthur Member Posts: 216
    robertshaw valve

    I had one once and what I found was that it's not the voltage open end that counts but the voltage while in circuit with the solenoid that counts, If it drops quite a lot then thats an indication,
    I use an old solenoid to test termocouple to see how good the couple is.
    But on a thermopile its a bit harded to do that you really have to take a reading on the Tp and Thtp terminals on the valve while its all connected.
  • Arthur
    Arthur Member Posts: 216
    Robertshaw Valve.

    It is a thermopile. A thermocouple only puts out about 30-40 MV A thermopile puts out up 750 MV A t/p is a multicollection of thermocouples bundled together to be able to produce the higher voltage. They work on the same principle, A thermopile can pull the gas valve open while a thermocouple can only just hold the valve open which why you have to hold the gas knob down after lighting the pilot to allow it time to generate enough voltage to hold the valve. With this valve you still have to hold the knob down to get the pilot to stay alight but once the pilot is going the main flame is controlled by the thermostat. Sometimes the T/P will generate enough juice to hold the pilot in but as soon as the thermostat calls for main flame the voltage falls away and you can lose the pilot as well as main flame.
    With that 750Mv output it points towards a faulty valve. Make sure the connection of the T/P into the valve is a good and tight connection.
  • Paul Ellison
    Paul Ellison Member Posts: 16
    Pilot FIXED!

    Thanks to everyone who helped (and to those who thought good thoughts as well). I made my first mistake by deciding the thermocouple that was replaced last fall couldn't be bad. It was. The real trick was finding one on a Saturday. I am proud to say I now have heat! The voltage was there but current is what holds the magnet. With cold finally approaching Ohio, I sincerely thank everyone - Have A Happy and Prosperous New Year!
  • Stay warm...

    ME
This discussion has been closed.