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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I have a Master Temp 250 pool heater that shows an AGS error on the back of the board. The heater runs for about 20 seconds then shuts off, any ideas?

AGS = Auto Gas Shutoff...
What is happening is the heater is monitoring (or sorta, by reasons difficult to explain here) Water Flow and Water Temperature. In this case, the AGS is triggered by a low water flow, or high Incoming Water Temp.
High internal water temp = triggered AGS.
If you have and can confirm, PROPER water flow, water temp coming into heater is Lower than 104°, then it is possible you have a faulty AGS.
But in most cases, it's only doing its job. Locate the reason for the fault, or why the AGS Switch turned the heater off.

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Have a Mastertemp 250, heard a bang, then water started leaking out of exaust. What could the problem be?

25620249-iwrnrkacomuoeuyhvucmvd0t-2-0_0.gif That is a diagram of the components of your heater.
Item #1 the Heat Coil or to be more precise, the Heat tube Sheet Coil Assembly Kit had BURST.
That is found within the tightly enclosed round chamber with the tightened securing screws on top and completely sealed with the Red Silicone sealant. Water is only to be in that coil assembly. When you heard the loud pop, it ruptured and water is now in the round chamber, which is a the Heat Chamber! Hot air exits that thru the exhaust, but you have water exiting now.

You can replace it yourself... it is a rather tedious job and laborious, but if your up to it, I think you may be able to do???
If not, call a service professional, preferably a Certified Pentair Tech, experienced in MasterTemp Tube Coil replacement.

I will include some pictures of the last one I performed a Heat Coil Replacement. If you choose to do it yourself, ensure that when you order a replacement kit, that it has a tube of High Heat/Temperature Silicone Sealant, the RED stuff. You will also need to know the date of manufacture of your specific heater!!! The kit changed back on January 12, 2009...
Pre that change date part # 460747
After that date, # 474059

Good Luck





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this heater will display 2 red light related problem 1-service the system mean you need to clean you filter, and service the heater mean it may be a problem with the heater this 2 you will be able to see it in key pad control the heater ,now reset the board and see what happens (CUT THE POWER ON/OFF UNCE )

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Raise temp above 120

Raising temperature above 120 degrees requires service call.
Or change dip switch settings and risk voiding warranty and causing service call expense.

Earliest versions of Rheem tankless 2006-8 let you set temperature up to 140 degrees F using remote.
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