Pls Help me troubleshoot my MasterTemp 400

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azpooldood

Member
Feb 26, 2024
6
Phoenix, AZ
1. Heater turning off gas every 60 sec. HLS light was on. Checked the thermostat and it was trashed, wouldn't open.
2. Got a new thermostat, but it's not opening until water temp is 145F. OK note to self, don't use cheap knockoff themostat from Amazon. Will order another.
3. Shorted the HLS to keep it running, and it turned off again, now with AGS light.

Question is, how do I tell if I really have an AGS issue, or if the sensor is just bad? Should I short it too?

Thanks!
 
ajw22 said:
Neither. AGS is indicating an internal overheat in the heater.

Shorting the sensors can damage the heater and is dangerous.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com www.troublefreepool.com
Click to expand...
Thank you for the insight. As I mentioned the thermostat doesn’t open until 145F or so (supposed to be 120F), would that cause the overheat you’re mentioning? I assumed shorting the HLS would bypass that.

Just trying to figure out if I need to buy any other parts aside from thermostat.
 
When you say the thermostat you mean the thermal regulator?

When was the last time you cleaned your filter?
 
azpooldood said:
1. Heater turning off gas every 60 sec. HLS light was on. Checked the thermostat and it was trashed, wouldn't open.
2. Got a new thermostat, but it's not opening until water temp is 145F. OK note to self, don't use cheap knockoff themostat from Amazon. Will order another.
3. Shorted the HLS to keep it running, and it turned off again, now with AGS light.

Question is, how do I tell if I really have an AGS issue, or if the sensor is just bad? Should I short it too?

Thanks!
Click to expand...
Thermal regulator (not a thermostat) is designed to keep the proper amount of water going through the heat exchanger so that it neither produces condensation nor water that is too hot coming out. If either the HLS or AGS (which almost never go bad unless they are damaged by poor chemistry) are opening, the water is too hot.
Dirty filter, water too slow from a VSP, broken internal bypass are the first items to check.
Always look at waterflow first before suspecting parts that are doing their job. You found a bad thermal regulator. That almost always is accompanied by a bad bypass as the spring on the bypass is subject to the same water as the thermal regulator, or it could be completely broken.
 
1poolman1 said:
Thermal regulator (not a thermostat) is designed to keep the proper amount of water going through the heat exchanger so that it neither produces condensation nor water that is too hot coming out. If either the HLS or AGS (which almost never go bad unless they are damaged by poor chemistry) are opening, the water is too hot.
Dirty filter, water too slow from a VSP, broken internal bypass are the first items to check.
Always look at waterflow first before suspecting parts that are doing their job. You found a bad thermal regulator. That almost always is accompanied by a bad bypass as the spring on the bypass is subject to the same water as the thermal regulator, or it could be completely broken.
Click to expand...
Thank you again. After replacing the thermo regulator, the gas stays on for much longer now. It heated the jacuzzi from 65F to 97F in about 30 min and never turned off, but once it hit 97F the HLS started triggering again and the gas goes on and off every 60 seconds. What would that indicate? Thanks!
 
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