Defective Thermocouple?

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    • #278271
      Gilbert Chacon

      Two months ago I replaced the Thermocouple on my HydroTherm Gas/Steam Furance. The old Thermoncouple was 5 years old. Last night the pilot light went out. I tried to relight it – it wouldn’t stay lit – I cleaned the Thermocouple and the orifice of pilot gas line and again tried to relight the pilot light – still wouldn’t stay lit.
      I purchased a new Honeywell Thermocouple and installed it. This time the pilot light stayed lit. In the past Thermocouples have lasted for 4 to 6 years – the one I replaced lasted 2 months. Was this Thermocouple defective or could there be some underlying problem that is causing the Thermocouple to fail?

    • #298166


      Like any other mass-produced device, including light bulbs, thermocouples may be defective and fail prematurely.

      That being said, other things can cause failure. I’ll name a few. The control valve could be faulty, but the fact that the problem resolved after a new TC was installed clears that suspect. Two other culprits deserve interogation…1) a kinked TC tube (connects to the control unit); and a excessively hot pilot flame (can damage the TC itself). Both are easily checked.


    • #298167

      Thermocouples can last 5 minutes or more than 5 years as they are a mass produced item, however check to see if the one you have has a larger than normal bulb in the area just under the gas valve as these one have a wax filled saftey cut off and will shut down if the main flame spills out the front panel for any reason such as a blocked flue etc.
      If this is the case then get the services of a suitably qualified gasfitter to correct your problem do NOT attempt this repair work yourself.

      Selgas Services Ltd
      Craftsman Gasfitters, Plumbers, Electrical Service Technicians

    • #298168

      Nick and Peter,

      Thanks for your help. I’m hoping it was just a defective Thermocouple. I didn’t find a larger than normal bulb on the old Thermocouple or the line kinked. Not sure about the excessively hot pilot light – I’ll keep that in mind if the new Thermocouple fails in the near future.


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