Minimax 400 potentiometer buzzing shutting heater off

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dis737

Member
Feb 23, 2021
5
LA
I have an old Pentair Minimax 400 (mid ‘90’s) and it won’t stay in heating mode.

It immediately starts up and ignites the burners but after about 15 minutes, the potentiometer dial starts buzzing and the heater shuts down. If I turn the dial hotter, it will typically kick on the heater again for a few more minutes, keep buzzing and then shut down again. The buzzing stops if I turn the dial back to colder. This happens with both the rocker switch in Pool mode or Spa mode.

My manual shows the whole control panel assembly as one item and does not list the pentiometer as an individual item. I do see a few vendors sell a Pentair potentiometer individually.

Any ideas if it is in fact the potentiometers that has gone bad or it it’s something else?
 
dis737 said:
I have an old Pentair Minimax 400 (mid ‘90’s) and it won’t stay in heating mode.

It immediately starts up and ignites the burners but after about 15 minutes, the potentiometer dial starts buzzing and the heater shuts down. If I turn the dial hotter, it will typically kick on the heater again for a few more minutes, keep buzzing and then shut down again. The buzzing stops if I turn the dial back to colder. This happens with both the rocker switch in Pool mode or Spa mode.

My manual shows the whole control panel assembly as one item and does not list the pentiometer as an individual item. I do see a few vendors sell a Pentair potentiometer individually.

Any ideas if it is in fact the potentiometers that has gone bad or it it’s something else?
Click to expand...
Sounds like the on-board relay may be failing. Omron g5le-14

You can get a aftermarket board for that heater for about $85.00 on Amazon:

TIROAR 470179​

 
dis737 said:
My control panel looks different than the one you suggested?
Click to expand...
Could be the S8600 Honeywell box, the gray IID box.
First pull each wire off of each terminal on the box and then replace it, one at a time so as to not get them confused. Sometimes that is all that is needed as it removes a bit of corrosion. "Fixed" many heaters with that box that way. If the box is bad, the new one is S8660K. Doesn't have to be purchased from a pool store as it is a standard HVAC part used in thousands of heaters.
 
dis737 said:
ok, will give that a try and report back.

BTW, the link below looks like the thermostat board on my unit

Click to expand...
Same relay is on that board as the one sent earlier. I missed that it is a 30-year-old heater. The relay sends 24V to the IID box so it can complete the ignition of the heater. Probably don't want to spend to much on an obsolete heater first made by Purex, bought by Pentair, discontinued when Pentair bought Sta-Rite.
 
Your first instinct was correct.

Went out and investigated further, the buzzing was coming from the relay on the thermostat board, not the potentiometer.

Ordered a new relay and have a shop near by that can solder it on.

Thanks again and I'll report back once I get it up and running again.

I hate to give up on a reliable heater that was worked so well over the years especially given the price of new heaters.
 
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