Question about Pentair Mastertemp Pool & Spa Heater Dual Electronic Ignition 400,000 Btu Lonox Propane 460737

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Mastertemp 250 service system light comes on when raised above water temperature

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  • hhgmaintenan Oct 16, 2010

    Thanks Greg, so what I need to do is change the thermocoupler? MIKE

  • hhgmaintenan Oct 16, 2010

    Thanks, the digital temperature now fluctuates up to 120 degrees and you can hear the water boil down by the inlet valve with a popping, crackling sound. So, your answer seems to hit right on. I'm glad I used this service and I thank you so much for the advice since its the weekend. Mike (Chief Engineer Holiday Inn Gulfport MS)



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This has something to do with a water temperature sensor which normally is a thermocouple.It seems that yours is reading the water temperature,sends a feedback signal to some sort of computer type controller,and when the heater output water starts getting a bit hotter than the temperature which it knows the water currently is,it's shutting down.Within thermocouples,there is a small section known as a reference temperature.That section sounds like it's gone bad because when comparing the temperatures and going above the reference,the best way to describe it is it's like popping a circuit breaker in your house,which causes shutdown,but in your house it's to prevent fire and/or save the housing wiring.In the pool heater,it's saving the water from boiling because it doesn't know when to stop.If you need more help or this is not correct,just comment back here and I will get an autolink to your post and reply ASAP.Good luck! Greg

Posted on Oct 16, 2010

  • Greg McCarthy Oct 16, 2010

    After I had shut down my computer,I realized i had forgot to ask you something.When you turn the temperature dial to attempt to heat up the pool,then the dial you are turning gets past the current water temperature,that is when the light appears?If so,then yes I would recommend the thermocouple.

  • Greg McCarthy Oct 16, 2010

    You are quite welcome sir.Now go enjoy your weekend.Greg



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