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Honeywell VS820A troubleshooting

gazzerp Member Posts: 14
Ten days ago, my girlfriend had a 90min power outage at her house. It became chilly that evening and when the boiler apparently hadn't done its job, I went to investigate. I found the pilot out and, as soon as I re-lit, it immediately went out again. I then began boiler troubleshooting 101...

The system: Utica PEG150 (older model) natural gas steam boiler. Battery-powered thermostat makes a connection between the hot-side of a 24v transformer and the safety controls (Honeywell Pressuretrol 169H, then to an M&M No. 2 LWCO) before reaching a Honeywell VS820A 1245 valve. Wiring on the valve is as follows: 24v in from LWCO to TH/PP terminal; and TH (upper left) terminal out to the transformer ground.

Troubleshooting performed thus far: Determined that the Powerpile was faulty (would not generate more than 510mv) so, replaced with new Q313A. Powerpile now generates 720mv when lit (disconnected from valve and holding the pilot valve open for about five minutes.)

With Powerpile disconnected and control wiring NOT connected, I read resistance on the valve as follows: between PP and TH/PP, 2.1 ohms; and between TH/PP and where the red, factory wire enters the power unit, 10.2 ohms.

With the thermostat calling for heat, I have 24.6v present at the valve. Proactively, I've already replaced the wiring between the thermostat/transformer and boiler cut-off switch (with new 18/2.)

With Powerpile connected and control wiring NOT connected, pilot stays lit and I read 620mv between the PP and TH/PP terminals. Same scenario but with a jumper between TH and TH/PP, I read 255mv between PP and TH/PP.

With both Powerpile and control wiring connected -but no call for heat- pilot stays lit and I read 565mv between PP and TH/PP. Same scenario but with a jumper between TH and TH/PP, I read 253mv between PP and TH/PP.

With both Powerpile and control wiring connected -but WITH a call for heat- the pilot immediately goes out and the valve emits a buzzing sound. I have not  yet attempted to re-light the pilot while the system is in this condition.

Respectfully, I seek some assistance: assuming I've taken my readings correctly, what do they tell you? Is the buzzing an obvious indicator, regardless of the readings? Should I attempt to re-light, after the pilot goes out (as described above)? Are there other tests/readings needed?

Thanks in advance.


  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    Sounds to me like you are mixing

    24 volts with millivolts. That gas valve a VS820 is designed for millivolts only.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    For troubleshooting procedures

    go to "Resources" and click then "Library" then "Tims Closet".
  • gazzerp
    gazzerp Member Posts: 14


    Turns out, I was able to get this far with already having read your "Procedures to Troubleshoot..." guide... so, thanks for that.

    As for the VS820A being a millivolt model... all I can say is that the system as I described has been in place for at least ten years - and worked fine until that power outage. (I assume that the Powerpile failing at that point was purely coincidental...)  In the Honeywell literature for the V800-series, I see references to 24v, line voltage as well as millivolt wiring. While my homeowner/DIY-er status precludes my knowing for sure that some form of "hybrid" installation (as I perceive mine to be?) won't work, I'd arrived at the belief that in my system the Powerpile milllivoltage is used to keep the pilot light valve open, then the control system voltage kicks-in to open the main burner valve. Am I wrong?

    I appreciate -in advance- your help.

    Thanks, Gary
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    The letter "S"

    in that valve number stands for "Self Generating" that is millivolts only so no matter how long it has been wired with 24 volts it is incorrect. Is the thermostat a 24 volt thermostat and if so how long has it been in place?

    If it has batteries then I assume it gets them recharge from a transformer.

    This system is incorrect no matter how you want to cut it. You need tpo get it rewired for total self generating which is to great advanctage with steam as it will work even when you have a power failure. The wiring is simple the generator goes to PP and then wire from the thermostat through the LWCO and pressuretrol to TH. That should work.

    I suggest getting a pro to take a look at it if you are not comfortable with my answer.
    Robert O'Connor_12Zman
  • gazzerp
    gazzerp Member Posts: 14
    edited May 2011

  • gazzerp
    gazzerp Member Posts: 14
    edited May 2011
    Humble pie...

    ... for my lunch today, I'm embarrassed to say.

    I rewired as you suggested and, when the main burner ignited, breathed a sigh of relief that -despite having paid attention to the "shorting-out" warnings in your document's instructions- I hadn't somehow damaged the valve.

    Being stubborn, though, I needed to figure out why it wouldn't work "the way it always had been wired." Yet, after an hour or so of messing with the thermostat (alkaline battery powered, listed for millivolt use,) I gave up. Confident that the wires were on the same terminals as before the power outage, I questioned whether I may have touched two "configuration" settings this thermostat has: a slide-switch on the back, for electric or gas, and another (firmware/push-button set) for air/hydronic (A/H) use. I just couldn't recall if I changed either/both when the system didn't fire back up after I swapped-out the generator. However, I tried each of the possible combinations yet was unable to get the system to function. One thing was clear, though: set to electric, the thermostat did not send 24v down to the valve (no buzzing) and the pilot remained lit. Set to gas, the 24v went to the valve, buzzed and the pilot went out. The A/H option made no difference, either way, for both electric and gas. Despite still having the piece of paper upon which I recorded the original wire colors/terminal letters mapping, it's clear I must have touched something. As stubborn as I can be, I decided to lick my wounds, reconnect with millivolt wiring only, used gas and hydronic settings, and walked away from it.

    Lesson learned: as in carpentry ("measure twice, cut once") -- draw a diagram, double-check all colors/markings/settings - then, touch.

    I regret having essentially wasted your time, Tim, but - my sincere thanks, anyway.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    Time is never wasted here

    at heatingHelp. Someone is always watching and listening and learning as we help others. Glad you did not do any damge to the powerpile valve. I have a feeling you did not have a complete circuit back to the 24 volt transformer is the reason that it would not work and also the reason you did not burn out the valve.
  • I need to verify the wiring of a vs820a 1047 connected on a hydrotherm hc125 and the prv and X-tank pressure settings. I am trying to help a neighbor who had no heat and a houseful of cold kids when I started. I replaced the gas valve, but saw that both wires from the high limit therm strapped on the outlet pipe from the boiler connected to the same therm contact (that just DOES NOT SEEM LIKE IT CAN WORK TO ME), with neither attached to power. I changed that, and the boiler appears to b functioning properly, but am nervous because I don't work on boilers. I also will have to change the bad prv and want to know the proper settings for it and the expansion tank, which still holds air.
  • icesailor
    icesailor Member Posts: 7,265

    "" I regret having essentially wasted your time, Tim, but - my sincere thanks, anyway. ""

    I read most everything. Especially if Tim is involved. You never know when a question provides the answer to someone reading here that you have no idea is reading.

    None of us are born knowing it. We all have to learn somehow. If no one asked questions, and no one ever answered them, none of us would know anything.
    Its nice to see someone that has a clue to what they are doing. As far as making referral drawings, I made them all the time. I never trusted them for a moment.

    "Measure Twice, Cut Once": Buy an Inch/Metric Rule. You'll make less mistakes and it is far easier to use. If you can count money, you can use a Metric Rule. How many fingers on your hands" How many toes on your feet? Unless you are like many cats I have had, you don't have 12 fingers or toes.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    Master plumber Mike, you want to make sure the high limit is wired in series with the thermostat. The wires from the pilot generator go to PP on the valve the therm/high limit go to TH.

    Did you take any millivolt readings? The procedure for that is included here on this site just read above postings for directions to my checkout procedure.
  • SherlockOhms
    SherlockOhms Member Posts: 13

    Sounds to me like you are mixing

    24 volts with millivolts. That gas valve a VS820 is designed for millivolts only.

    All the reading and measuring ohms and volts is something I never do and I get almost no call backs, I use a AAA battery to test my gas valves, if they are good they work f not they are bad.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    I encourage folks to do a complete analysis on Powerpile systems as they can be tricky. As someone who has been troubleshooting these systems for over 50 years and teaching about them for half that time I still take a complete set of millivolt readings on every job.
  • Hugeman1
    Hugeman1 Member Posts: 1
    Hi Guys!
    My friend is just moving into an older home with Utica gas boiler( model PGB 125A) , rated at 125,000 BTU/hr.(input) It has a VS820A- 1054 gas control valve ( with an oper of VS824A and a reg of VS308A). The house had been empty for quite a while, and the gas co technician, when he came too turn the meter on, said the gas had been off quite a while. The tech said he can't test the valve, but it might be bad, because the pilot will not stay lit. Question-- could these valves go bad just from no use of gas system? and what is the best way to test if the valve is bad. Alternatively, can we disconnect it and clean it out ( the valve)? we can get a valve for about $180.00, but we're not yet sure that's the problem. The gas co tech said the problem could also be in the manifold ( after the valve). So, we'll go one step at a time. Any suggestions? Thanking you ahead of time.