Mastertemp 400 Wrong Temperature Readings

[1poolman1]

From the Pentair manual on why an AGS trips: "Water temperature after the 2nd pass thru the heat exchanger is more than 140°F."
They are a purely mechanical switch that opens when the high temperature is sensed. If you have replaced it, or exchanged with a known good one, it highly indicates a water-flow issue. That may be internal to the heater or external to your equipment.

To quote virtually every heater school I ever attended, "Ninety percent of all service calls on heaters have nothing to do with the heater but can be traced to a water-flow problem." Newer heaters have the same issue, but the water-flow issue is internal because of new designs.

 

[mflores83]

It sounds like you have a blocked downstream internally or externally. Causing the water in the exchanger to back up into the top of the manifold. That’s where your ags and thermistor are.

Would I not notice that with reduced water pressure in the cleaning heads and the spa jets?

 

[mflores83]

Some pictures of the system.

 

[Poolbreh]

That looks like a bypass

 

[mflores83]

That looks like a bypass

How should it be? It is in the fully open position. I recall it being partially closed before. I moved it to this position and the heater is working. Thanks in advance and thankfully Amazon allows returns lol

 

[Poolbreh]

Perpendicular is closed, parallel is open. You want 40gpm traveling through heater.

 

[JamesW]

Looks like a bypass.

It needs to be fully or partially closed depending on the speed of the pump.

Fully closed for slower speeds and partially closed for higher pump speeds.

 

[Johndenver]

Hello did you figure out what the problem was. Mine is doing the same thing.

 

[JamesW]

Hello did you figure out what the problem was. Mine is doing the same thing.

The external bypass was open.