Newbie here - how does the Pentair Minimax Flow Valve work

[Granite80]

Hi

I am brand new to the forum, but looking forward to the wealth of knowledge here.

I live in Phoenix and bought a house with a large (~40,000 gal) pool + spa + water feature.

Recently I have been having trouble with my Pentair Minimax 400 short cycling. I pulled the flow valve today and the bottom part (outlet side) is very rusted. I put it in some hot water (~190 degrees F) and saw no movement of the device, so I assume it is bad so have a new on on order.

Question for the gurus here: am I correct in understanding the operation of this flow valve as follows:
1. At cool temps the valve is open, allowing some water to bypass the heater and therefore the reduced amount of water flowing through the heat exchanger gets warmer faster
2. As the water outlet temp increases, the valve closes, forcing more (all?) of the water to flow through the heater core.

Is this right? I am assuming this operates like the thermostat on a car, but looking for confirmation or someone to explain how it really works.

If my understanding of the flow valve operation is correct it seems that the reason the heater is short cycling is not enough of the hot water is exiting the heater (on its way to the spa), so the temp is building up at the outlet and tripping the high temp limit switches.

Thanks in advance!

 

[Bama Rambler]

You're pretty much right in how the flow valve works.

Here's a link to the service manual. On page 42 there's a write-up on how it works and how to troubleshoot it. If you placed it in hot and then cold water and it didn't move at all, you have a defective flow valve.

 

[Granite80]

Thanks!