Please HELP: Pentair Mastertemp 400 heater problem that I can't figure out

GLGreen

New member
Apr 16, 2025
2
Tucson, AZ
Hello all, when I go to heat up my jacuzzi from my shared Pool/Jacuzzi Pentair Mastertemp 400 with valves set to jacuzzi mode, the burner will come on and start heating for a minute or two, then shuts down the heat and gives an HLS/AGS error LED lit on the circuit board. I have followed the diagnostic flowchart and replaced the HLS, AGS, and the thermostat/spring assy. Presently, still shuts down the same way with the same failure mode. There is one thing that might be significant and that is if you run the shared heater with the valves set to heat the pool, the error will not occur and the heater will run as long as you want it too. Also, the 4 cartridge filters are only 6 months old, and I just cleaned them a week ago to take them out of the discussion for possibly lack of water flow. Out of ideas, need some professional advice. Regards and Thanks in advance.
 
Welcome to TFP.

What model pump do you have?

Show us pictures of your equipment pad.

Do a Overnight Chlorine Loss Test to see if you have an algae problem clogging your filter. If you fail you need to follow the SLAM Process

You have a water flow problem due to the increased “head” of your spa jets.
 
Seems like a flow problem.

Show all equipment.

What pump?

What pump speed?

What is the filter pressure when heating?
Thanks for any help in advance and Regards
 

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