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Lochinvar Noble - not space heating - solved

ben1272 Member Posts: 3
I am just posting this in case it helps someone else, as I have resolved my problem. I'm not even sure how to fully describe it, but here goes:

On the water input side to the boiler (space heat) there is a small temp sensor that glows red when it is tripped. On my system, it just clips on top of a small brass/copper nipple-like extension off of the main flange assembly. Some surface corrosion was making it so that this small temp sensor could not accurately measure the inlet water temp and was keeping my boiler from firing to make heat for the house. I popped the snsor clip off, wire brushed the surface of the nipple and slid the sensor back on, and voila! Back in business.

I guess I would have found this problem sooner had I just checked the function of all the system sensors, but I ran down all sorts of dead ends checking things like setpoint temps., outdoor reset enable/disable, etc. In the end, a dirty pipe was keeping the temp sensor from reading the right temp.

Simple fix, just know to look for it! Hope this helps someone.



  • ben1272
    ben1272 Member Posts: 3
    OK....looked into it further. I think this sensor is a flow sensor for the DHW. It seems to have been stuck on, possible from some water getting into it and corroding its co-located circuit board. I guess red-lit means it sees flow which means turn off the heat and turn on the DHW.

    I have the sensor off of the nipple it normally rides on and plan to dis-assemble and hopefully clean corrosion off the PCB using some cleaner/alcohol. I will post what happens. If it still isnt working right I will buy a new sensor. Apparently the gasket on the space heat boiler right above is leaking and dripping onto this little flow sensor. So I need to replace a pipe seal/gasket also.

    All this is good to know and hopefully helpful to someone.

    I might have found this problem sooner but I have a series electric hot water tank that essentially acts like a 40 gallon holding tank with maintenance heat. Without it, I may have noticed my DHW was flaky sooner!
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,563
    Thanks Ben
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • ben1272
    ben1272 Member Posts: 3
    OK....a little more info. The DHW flow sensor circuit board does not show any sign of corrosion on it. The water that is dripping from above ( the leaky boiler fitting/gasket above) seems to have been only corroding the copper/brass nipple/nut that the flow sensor sits on. Maybe this corrosion was causing the problem, but I cleaned it off and the flow sensor was still stuck on. Then, i rotated the flow sensor to the 180 degree opposite side of the nipple and it shut off. In this position it seems to be working.....when I turn on a hot faucet it lights red instantly, When i shut off the faucet it extinguishes immediately, as it should. Seems to be working now. Maybe it needs to be in this position to work properly? Or maybe there is some scale buildup inside the nipple that is preventing it from working properly when it is positioned on the other side? Not sure. Just be sure to inspect yours if you are having a similar problem!
  • Do you have a picture?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    EBEBRATT-Ed Member Posts: 15,317

    Somewhere in the Lochinvar literature should be a chart showing the resistance of that sensor at various temperatures.

    If you clean the sensor and the pipe and reattach it then measure the temperature of that pipe disconnect bot sensor wires and put an ohm meter on it and compare it to the chart