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Replaced thermopile, voltage still too low

Dante_2
Dante_2 Member Posts: 12
I have an 86 year old steam boiler with a Honeywell Powerpile VS820 (replaced in 2016). The pilot stays lit, but the voltage is too low to open the gas valve. It's a 750mV system. The open voltage was 480mV using the pilot as the heat source. The thermopile was a Q313A1625 which I can find absolutely no information on. I took it out and hit it with a MAPP torch and it quickly passed 850mV. I don't know if that means anything, but I went down to the local heating place and bought a new Q313A1188. It seems about the same except the wires are 35" instead of 47". I installed it, but the open voltage is exactly 500mV. The pilot light looks healthy to me or at least the same as it always did. The position of the thermopile in relation to the pilot is not adjustable. I tried opening the pilot valve, but that only gained a few mV. I have my notes from 2016 when I was troubleshooting this system. The open voltage was 750mV. I replaced the VS820 and everything has been fine and untouched until now. What could I be missing?

Comments

  • Big Ed_4
    Big Ed_4 Member Posts: 2,783
    edited October 2021
    Maybe the pilot flame is too small ?
    I have enough experience to know , that I dont know it all
  • Dante_2
    Dante_2 Member Posts: 12
    I ran the pilot valve from nearly closed to fully open and it didn't make much difference in voltage or flame size. The flame is blue and about 2 inches.
  • mattmia2
    mattmia2 Member Posts: 9,627
    Is the pilot burner clean? Are you using the same meter as 7 years ago?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,516
    You have to measure the voltage when it is trying to open the valve. Check all the wiring connections at the thermostat, high limit and low water cutoff.

    They work on low current and voltage a little to much resistance somewhere and the valve may not open. Could be a bad gas valve as well
  • HomerJSmith
    HomerJSmith Member Posts: 2,438
    What else is in the circuit that may be creating resistance?
    unclejohn
  • retiredguy
    retiredguy Member Posts: 902
    If you have an older thermostat that has the mercury bulb for the contacts, the mercury could be oxidizing and adding resistance. If you replaced any control that is part of the control circuit make sure that you used a control that is made for a thermopile system and not a standard "off the shelf" control. A lot of the older controls had "gold flashed" contacts to reduce the contacts resistance. Make sure that all wires and wire connection points are clean and tight. When making wire connections, scrape the ends of the copper wire to remove anything that will add to the resistance. If you can, post a picture of the pilot flame so we can see what the flame looks like and make sure that the pilot flame is blue and not yellow to get max heat. As a last resort, you can substitute a flashlight battery as a power source, instead of the powerpile, to check the gas valve's operation.
  • Chris_L
    Chris_L Member Posts: 336
    Here is the Bible for anyone troubleshooting millivolt systems: https://heatinghelp.com/assets/documents/Procedures-for-Troubleshooting-Powerpile-Systems2.pdf

    Is the 500 mV measurement with the powerpile holding the pilot? If so, that doesn't sound bad. Under those conditions, the powerpile hooked up to my VS820C gas valve reads 520 mV, and the system works fine.

    Are you jumping the thermostat terminals on the gas valve to test it? That will tell you if the problem is in the operating controls or not.

    A picture would be helpful to see if the pilot flame is hitting the powerpile properly.
    Alan (California Radiant) Forbes
  • fxrgrunt
    fxrgrunt Member Posts: 157
    Dante_2 said:

    I have an 86 year old steam boiler with a Honeywell Powerpile VS820 (replaced in 2016). The pilot stays lit, but the voltage is too low to open the gas valve. It's a 750mV system. The open voltage was 480mV using the pilot as the heat source. The thermopile was a Q313A1625 which I can find absolutely no information on. I took it out and hit it with a MAPP torch and it quickly passed 850mV. I don't know if that means anything, but I went down to the local heating place and bought a new Q313A1188. It seems about the same except the wires are 35" instead of 47". I installed it, but the open voltage is exactly 500mV. The pilot light looks healthy to me or at least the same as it always did. The position of the thermopile in relation to the pilot is not adjustable. I tried opening the pilot valve, but that only gained a few mV. I have my notes from 2016 when I was troubleshooting this system. The open voltage was 750mV. I replaced the VS820 and everything has been fine and untouched until now. What could I be missing?

    I would like to see some pictures of this old boiler.
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 9,627
    Chris_L said:


    Is the 500 mV measurement with the powerpile holding the pilot? If so, that doesn't sound bad.

    My assumption was that this system didn't have a pilot valve for the thermopile to hold...
  • Chris_L
    Chris_L Member Posts: 336
    mattmia2 said:

    Chris_L said:


    Is the 500 mV measurement with the powerpile holding the pilot? If so, that doesn't sound bad.

    My assumption was that this system didn't have a pilot valve for the thermopile to hold...
    The VS820 is a combination gas valve that feeds both the pilot and the main burner. See:https://manualzz.com/doc/3213624/honeywell-vs820-user-s-manual

    I was assuming that is the way the OP is using it. And that could explain the difference between the true open circuit voltage (the pp not attached to the gas valve at all) and the voltage when attached to the gas valve and keeping only the pilot valve open.
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 9,627
    I didn't see the valve model. I thought it was still a pre-total shutoff system.
  • Dante_2
    Dante_2 Member Posts: 12
    mattmia2 said:

    Is the pilot burner clean? Are you using the same meter as 7 years ago?

    The burner looks clean and the flame seems good. The meter is the same.

    You have to measure the voltage when it is trying to open the valve. Check all the wiring connections at the thermostat, high limit and low water cutoff.

    They work on low current and voltage a little to much resistance somewhere and the valve may not open. Could be a bad gas valve as well

    If you have an older thermostat that has the mercury bulb for the contacts, the mercury could be oxidizing and adding resistance. If you replaced any control that is part of the control circuit make sure that you used a control that is made for a thermopile system and not a standard "off the shelf" control. A lot of the older controls had "gold flashed" contacts to reduce the contacts resistance. Make sure that all wires and wire connection points are clean and tight. When making wire connections, scrape the ends of the copper wire to remove anything that will add to the resistance. If you can, post a picture of the pilot flame so we can see what the flame looks like and make sure that the pilot flame is blue and not yellow to get max heat. As a last resort, you can substitute a flashlight battery as a power source, instead of the powerpile, to check the gas valve's operation.

    By open voltage I mean the pilot is on the thermopile, but the wires are not connected to anything. I use a piece of wood to hold down the pilot valve and let it warm up to check it. 500mV is out of spec. The thermostat is a programmable electronic one with a relay inside that makes the connection. It is the same one that's been there for years. I understand all the control devices will cause a voltage drop, but I am testing without any controls. The gas valve does work. The pilot flame is blue.
    Chris_L said:

    Here is the Bible for anyone troubleshooting millivolt systems: https://heatinghelp.com/assets/documents/Procedures-for-Troubleshooting-Powerpile-Systems2.pdf

    Is the 500 mV measurement with the powerpile holding the pilot? If so, that doesn't sound bad. Under those conditions, the powerpile hooked up to my VS820C gas valve reads 520 mV, and the system works fine.

    Are you jumping the thermostat terminals on the gas valve to test it? That will tell you if the problem is in the operating controls or not.

    A picture would be helpful to see if the pilot flame is hitting the powerpile properly.

    That document is what I used a few years ago and I had my voltages written on it. No, the 500mV is with pilot valve held manually and thermopile disconnected completely. That document states it should 540 minimum. With it holding the pilot valve open it is only 380mV. It is enough to hold the valve open if I jump it, but not enough to open itself reliably. The gas valve works and the controls work. Here is a picture of the pilot flame. Here is a picture of it https://ibb.co/vm7ychn
    It seems to be impossible to get a picture of the flame and the thermopile at the same time. Here some pictures I posted here a few years ago https://goo.gl/photos/4pycTnc1ytznWXeb7 Now that I look at the old pics it does seem the pilot was stronger then. I see how the blue flame wraps around the thermopile. I think this might be where my problem is.
    fxrgrunt said:

    I would like to see some pictures of this old boiler.

    https://goo.gl/photos/4pycTnc1ytznWXeb7
  • mattmia2
    mattmia2 Member Posts: 9,627
    Dante_2 said:

    With it holding the pilot valve open it is only 380mV. It is enough to hold the valve open if I jump it, but not enough to open itself reliably. The gas valve works and the controls work.

    What do you mean by jump it, you mean jumper the terminals on the gas valve for the thermostat and safties, like tt?
  • Dante_2
    Dante_2 Member Posts: 12
    mattmia2 said:

    Dante_2 said:

    With it holding the pilot valve open it is only 380mV. It is enough to hold the valve open if I jump it, but not enough to open itself reliably. The gas valve works and the controls work.

    What do you mean by jump it, you mean jumper the terminals on the gas valve for the thermostat and safties, like tt?
    Yes, if I bypass the controls and jump the gas valve to the thermopile. It will usually click on and then I let it go and it will stay on for that cycle. Today it has been working on its own, but I doubt it will be reliable at that low voltage. I'm wondering now if the new Honeywell thermopile I got is bad. It was in a sealed package, but the rubber band holding it coiled up was so old it crumbled in pieces.
  • Chris_L
    Chris_L Member Posts: 336
    Did you test this thermopile with a torch, or just the old one? That should tell you the maximum output you can expect. If the output is no better than what you measure open circuit with the pilot flame on it, I'd try another one.

    Your pilot flame is hard to see in the picture, but it doesn't look that big. I am surprised you couldn't adjust it much. (I hope you didn't make the same mistake I did, and adjusted the main gas output instead of the pilot gas output.) Although you do get to a point where more gas to the pilot doesn't affect the mV output much.

    If the new thermopile has good output with a torch, you should check the pilot gas tube to be sure it is not clogged or kinked. And only the tip of the thermopile should be in the flame.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,516
    @Dante_2

    I think you answered you own question. If it works when you jump it and bypass the stat & safety's but is not reliable when they are in the circuit then it sounds to me like you have too much resistance in the safety/thermostat circuit.

    Measure the voltage when jumped and then measure the voltage across the circuit when the safeties and thermostat are in the circuit and see what the difference is
    mattmia2
  • Dante_2
    Dante_2 Member Posts: 12
    Chris_L said:

    Did you test this thermopile with a torch, or just the old one? That should tell you the maximum output you can expect. If the output is no better than what you measure open circuit with the pilot flame on it, I'd try another one.

    Your pilot flame is hard to see in the picture, but it doesn't look that big. I am surprised you couldn't adjust it much. (I hope you didn't make the same mistake I did, and adjusted the main gas output instead of the pilot gas output.) Although you do get to a point where more gas to the pilot doesn't affect the mV output much.

    If the new thermopile has good output with a torch, you should check the pilot gas tube to be sure it is not clogged or kinked. And only the tip of the thermopile should be in the flame.

    I did not test the new one with a torch because I didn't know how accurate it is. I think the torch is much hotter than the pilot so maybe even a bad thermopile will read good with a torch. Also, I didn't know if it can be damaged by excessive heat.

    I may or may not have made the same mistake as you and then realized it and corrected it. I got the flame bigger, but it didn't make much difference in voltage.
  • Chris_L
    Chris_L Member Posts: 336
    Dante_2 said:


    I did not test the new one with a torch because I didn't know how accurate it is. I think the torch is much hotter than the pilot so maybe even a bad thermopile will read good with a torch. Also, I didn't know if it can be damaged by excessive heat.

    I don't think you have to worry too much about damaging the powerpile when testing with a torch. Just don't overdo it with the heat. See: https://www.youtube.com/watch?v=63zFDe6P1bk

    If the open voltage of the original powerpile (480 mV) in the pilot was under the same conditions as the new one in the pilot (500 mV), with the wires disconnected from the gas valve in both cases, that suggests the powerpiles are not the problem. (The fact that the original one does produce enough voltage when heated with the torch also supports this.)

    More likely, the powerpile is not getting enough heat from the pilot flame, so it does produce enough voltage to operate the gas valve when the wires are attached. Is the gas pressure ok?
  • Dante_2
    Dante_2 Member Posts: 12
    The voltage is still low, but it has been coming on reliably all week. I'm going to just leave it alone unless it acts up again.
  • mattmia2
    mattmia2 Member Posts: 9,627
    If the thermostat is mechanical contacts instead of a mercury bulb you could try cleaning the contacts with a think piece of cardboard with some alcohol or contact cleaner on it, like a business card or postcard to polish any oxide off them. It wouldn't take much oxide to cause enough voltage drop to make it unreliable.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,516
    Why not jump the stat and or limits and check the voltage? That will tell you if it's high resistance or a thermopile issue
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 9,627
    The voltage across tt or however the thermostat connection with it calling will tell you more. If it is a few tens of mv it is probably ok, if it is hundreds of millivolts then there is a bad contact or connection somewhere.
  • Chris_L
    Chris_L Member Posts: 336
    The OP measured the original thermopile in the pilot with nothing connected to it but the voltmeter and got 480 mV. He then bought a new thermopile and made the same measurement. It was 500 mV. In both cases, that is too low.

    When he tested the original thermopile with a torch, he got 850 mV. (He didn't test the new one with the torch.) This seems to indicate that the pilot is weak or the thermopile is not positioned correctly in it.

    While there might be problems with the connections, he needs to get the thermopile voltage up to spec first.
    mattmia2
  • pecmsg
    pecmsg Member Posts: 4,842
    edited November 2021
    Dante_2 said:
    86 Years..............Its had a good life but is what maybe 40% efficient?

    Replace it with a new boiler, this it's the rare occasion that you'll actually see a return on investment in energy savings.
  • Mr_TA
    Mr_TA Member Posts: 44
    edited February 2023
    I have a similar problem. When I press down the pilot knob and disconnect the wires from the terminals, it only reads about 300mv. If I connect the wires and release the knob, the pilot stays on, but it's around 220mv. Needless to say, the gas valve does not open or make any sounds whatsoever.
    When I heat it with a small torch in addition to the pilot light, it becomes glowing red hot, and reads about 350mv (loaded with the pilot valve). Still, no response from the gas valve whatsoever.
    Everything else seems to work - the pump runs, the relay clicks, the thermostat circuit is closed, etc.

    This is a brand new powerpile which I bought at the G about 2 years ago but only installed now. Do they go bad from just sitting around? I don't think they'll return or replace it, but I'm thinking of trying to anyway, at least before ordering another one.
    It's the ROBERTSHAW model 2EWG1. Is that a bad brand? Should I look at different brand for powerpiles? Is Honeywell better?
    Thank you in advance for any information.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,516
    Nothing wrong with Robt. Shaw. Never herd of one going bad sitting around but anything possible
  • Mr_TA
    Mr_TA Member Posts: 44
    Perhaps just my luck of getting that one defective part.
    Normally, should the element start glowing red? Or is that too hot? I'm trying to figure out if the pilot flame is too weak, but I was unable to raise the voltage above 350mv even with a torch.
  • Chris_L
    Chris_L Member Posts: 336
    But when you got that 350 mV reading using the torch, it was still connected to the gas valve. What is the reading when using the torch with the powerpile connected only to the meter?

    That is what you should be using to test the powerpile alone. The low mV reading you get when it is connected to the gas valve could simply mean there is something wrong elsewhere in the circuit.
    Mr_TA
  • Mr_TA
    Mr_TA Member Posts: 44
    edited March 2023
    OK I took the new Robert Shaw powerpile off, and held it next to my gas range in the kitchen burning at full blast, and it never went up above 350mv.
    The old Honeywell that I had thought was broken, quickly went up to 700mv and stayed there.
    I think it was the position of the pilot light all along that was the problem and I blamed the powerpile for no reason. The light is nice and blue, and has a good size, so the only thing I can think of is that it's not heating the powerpile in the right place.
  • Chris_L
    Chris_L Member Posts: 336
    So try the old one on the boiler, again not connected to anything but the meter, heated by the pilot manually held open, and see what voltage you get.

    If the voltage is low, it might be the position of the powerpile--only the tip should be in the flame--or the gas flow to the pilot might not be sufficient--there should be a strong blue flame.
    Mr_TA
  • Mr_TA
    Mr_TA Member Posts: 44
    edited March 2023
    Final update: turned out the problem was caused by the mounting "sleeve" (attached image). It's way too long and didn't leave enough of the PP element exposed to the fire. It worked at first, but I think due to natural degradation of the old Hw power pile, at some point it no longer produced enough voltage. I shortened the sleeve with a grinder and the boiler works perfectly well now (with the old Hw PP). I also confirmed that the RS one is defective - just my luck, I guess. Thank you all for the help.
  • Tim McElwain
    Tim McElwain Member Posts: 4,621
    Just wanted to let you know this is one of my trouble shooting guides. Here is the Bible for anyone troubleshooting millivolt systems: https://heatinghelp.com/assets/documents/Procedures-for-Troubleshooting-Powerpile-Systems2.pdf
    Mr_TA