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Gas boiler that works for a while then shuts down

PicklemanPickleman Member Posts: 12
I have a natural gas boiler that I'm having trouble with. The homeowner said this problem would only happen once a year or so, but now its every day. The boiler will run after shutting the emergency switch off and turning back on. But then will turn off at some point there after. I am having the homeowner see how long it runs before shutting off as of right now. The Boiler is most likely 20 years old with no roll out switches at the burner or draft inducer. It is tied to a field control fan in the can along with a natural gas 50 gallon water heater. It looks to me like the boiler is connected to the F.I.C. ok with a thermostat wire running to it from the thermostat and then another wire running back with mini volt signal to fire burner (It has a thermocouple with the two wire set up to gas valve). I forgot to see if the gauge of the wire was correct 16 for one and 18 for the other to and from F.I.C. The water heater is tied to F.I.C. with a vacuum style switch using 110 volt from H terminal back to M terminal. I'm thinking that the boiler with shut off when water heater runs, but not sure. I wasn't able to hang around long enough to see it shut off.
I'm not sure if its a bad gas valve, thermocouple, aquastat, thermostat wire too small....any ideas?? Thanks, Jay


  • icesailoricesailor Member Posts: 7,265
    There has to be some sort of a "board" in the system (like maybe in the FIC that resets after you kill the power if there is a problem. Trace the power backwards from there the signal comes from to start the burner.
  • PicklemanPickleman Member Posts: 12
    I was trying to do that yesterday not realizing that it was mini volt. I wasn't getting a reading on my meter. I pretty much gave up on it, but my customer insists on 'me' fixing it! I'll have to switch my settings to get a reading.
  • wogpa67wogpa67 Member Posts: 238
    check the pressure switch in the FIC. It may be opening during the heat call
  • ZmanZman Member Posts: 5,830
    I think it is likely that the controller is set up to lock out after it has a few failures to ignite. When it it powered off and on it resets. Look for an ignition or thermocouple issue
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • wogpa67wogpa67 Member Posts: 238
    Some of those first induced draft boilers had a sail switch in the inducer housing. Is it a crown boiler by chance?
  • PicklemanPickleman Member Posts: 12
    I can't remember the name of the boiler for some reason. I don't think it's a crown. There are no roll out switches anywhere. The burner actually works fine no problems igniting just would not stay running long term. Seemed more to me that there was intermittent power signal to the gas valve. I'm not sure if the pressure switch is working ok in the FIC. I did bypass the T3 and T4 terminal mini volt signal from the FIC to boiler as a temporary fix today. Tied the gas valve to the B1 and B2 in the Aquastat. It seemed to work fine. Time will tell. Would changing the pressure switch in the FIC fix this or is it more the relay in the FIC?

    Thanks for all the responses!
  • PicklemanPickleman Member Posts: 12
    Spoke to Field control tech support seems likely that the Pressure switch is bad like wogpa67 says. Thanks again!
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