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Thread: Help troubleshooting Mastertemp 400.

  1. Back To Top    #1

    Help troubleshooting Mastertemp 400.


    Went to go use SPA last night and found it wasn't getting hot. Turned off heater and then back on and it fired up for a few minutes and then turned back off. Service Light was on.

    Initial error was HLS (High Limit Switch). I temporarily bypassed that switch to see if it was the issue (bad switch?). The unit fired up and ran for longer but then turned off with a AGS (automatic gas shutoff switch) error. It is my understanding that this just another temperature sensor to turn off the gas. Just a 2nd level of fail safe?

    Is it possible that both they HLS and the AGS switches have become bad or is this the sign of another problem with maybe the regulator?

    How do you get access to the regulator? It seems to be that 3rd plastic output port but couldn't figure out what tool was used to open it other then just a pair of pliers? Any tricks to that? I tried with a screw driver across the slots but it didn't budge and I didn't want to damage it.

    So, to me it seems that things are getting too hot. The flow in the spa is good and the pump basket is clean.. It does not run through filter, its just the SPA pump/Jets. (I know, I'm going to change this).

    What else should I check? Should I replace HLS and AGS? I have recently replaced control board and ignition module due due to lightening strike prior to us buying the house.



  2. Back To Top    #2

    Re: Help troubleshooting Mastertemp 400.

    Seems like it might be the regulator/thermostat. Took out the regulator and am running it without regulator (this should just make it very inefficient AFAIK, but still work properly) and it appears to be running just fine.

    Here are some pictures of the regulator. There is some slight rust and discoloration on the thermostat.

    So, should I replace the thermostat?


    Attached Images Attached Images

  3. Back To Top    #3

    Re: Help troubleshooting Mastertemp 400.

    Replaced the thermostat and all is well. Brought the spa up to temperature just fine without any faults. Just putting this here to other searching can know the result. The part was about $40 online. Use a big screwdriver to unscrew the cap and replace. I was able to confirm it was the issue by first running it with no thermostat in place. This will just make it very inefficient but will still work.



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    Re: Help troubleshooting Mastertemp 400.

    Just to clarify, the regulator was the only part replaced. You did not replace HLS or AGS.

  5. Back To Top    #5

    Re: Help troubleshooting Mastertemp 400.

    As an FYI, removed thermal regulator and all was well. Replacement ordered.

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