Mini Max Plus 400 Theristor Probe

[Brandon Penland]

I typically try to keep my pool heated at around 85°. Today, I noticed that the pool was cooler as the heater was not maintaining the temperature.

When I turned the dial up on the heater, it did turn on. It just seems that the temperature is not being read correctly. Usually, I turn the dial back around four notches and that is the right temperature to maintain at 85 degrees.

This time, just to get the heater to turn on, I had to dial it back and only one notch which would normally only be a very high temperature.

Since the heater has two dials, one for spa and one for pool, I tried them both. They were doing the exact same thing.

From research, it sounds like I just need to replace the thermistor probe. Just thought I would check in with the group and see thoughts?

 

[Brandon Penland]

Below is a picture of my unit. All of a sudden, the heater will not kick on unless the dial is turned all the way up to the last units.

 

[Brandon Penland]

OK, I ordered a brand new thermistor probe and installed it. I really thought this had to be the issue. Unfortunately, the heater is doing the same thing. It is only clicking on when I turn the knob pretty close to full heat. it seems like it’s not recognizing lower temperatures. Does anyone have any other ideas as to what would cause this?

Does the new thermistor take time to acclimate to temperature before it reads correctly?

 

[ajw22]

Is your Minimax a millivolt unit?

The knob controls a potentiometer, which is a variable resistor. You can try spraying it with contact cleaner which sometimes gets it working.

Replacing it looks to cost $29.

Pentair 471678 Minimax MV Potentiometer

The Pentair 471678 Minimax MV Potentiometer is an excellent choice for your pool filter needs this year! Get yours today from Pool Warehouse!

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Maybe @swamprat69 has ideas.

 

[Brandon Penland]

Is your Minimax a millivolt unit?

The knob controls a potentiometer, which is a variable resistor. You can try spraying it with contact cleaner which sometimes gets it working.

Replacing it looks to cost $29.

Pentair 471678 Minimax MV Potentiometer

The Pentair 471678 Minimax MV Potentiometer is an excellent choice for your pool filter needs this year! Get yours today from Pool Warehouse!

www.poolwarehouse.com

Maybe @swamprat69 has ideas.

It is actually a mini max plus 400. It is an older unit. Both knobs, on made to direct to spa, one to pool both having same behavior at the same time.

 

[Brandon Penland]

Is your Minimax a millivolt unit?

The knob controls a potentiometer, which is a variable resistor. You can try spraying it with contact cleaner which sometimes gets it working.

Replacing it looks to cost $29.

Pentair 471678 Minimax MV Potentiometer

The Pentair 471678 Minimax MV Potentiometer is an excellent choice for your pool filter needs this year! Get yours today from Pool Warehouse!

www.poolwarehouse.com

Maybe @swamprat69 has ideas.

I took the knob off and sprayed it with contact cleaner underneath. I also squirted a bit inside the cylinder where the knob is mounted. Thank you for the suggestion. It completely worked! Seems to work better than before. I honestly did not think this was the problem. I gave both knobs the same treatment and they now both work.

I’m curious, The knob has a metal mounting in the center. It brushes against a metal plate that has a void in it through the middle. I can’t figure out for the life of me how cleaning that actually made it work.

Sometimes I just like to learn stuff. Why would cleaning underneath the knob make the ponteniometer work again? Does the contact with the metal inside the knob against the metal plate how it works?

 

[ajw22]

The wiper moves along a variable resistor that tells the board the temperature you desire.

You cleaned the wiper contact.

 

[Brandon Penland]

Thanks for the help. I believe I get it now!