MiniMax NT 400 wont start

Paul Comi

Member
May 15, 2020
11
Southern California
Hello all. I have an in ground pool with a roughly 10 year old Pentair MiniMax 400 NT heater After two days of trying unsuccessfully to diagnose why my heater isn't working I'm here.

two years ago (12/2018) I was having starting problems and after speaking with pentair I installed a new igniter and it worked. The igniter appears to be a ceramic heating element which heats up and glows red hot. It's not a spark style igniter fwiw. we don't heat the pool or spa during the winter so it hasnt been used for 4-6 months.

Initially I got the heater to start two days ago, but after trying to start it again and until now two days later the unit goes through this sequence: fan/blower blows, thermostat led indicator lights up, temperature appears on the display, and no clicking to start sound like usual. When I cut the power to the unit and attempt to cycle over I have seen a glow which I assume is the igniter but it goes dark and the heating light never comes on

so far I have pulled the top of the unit and checked wiring, checked the tube to ensure it's connected to the fan, and the last thing I tried was to jump the pressure switch that is at the gas input. Also since my thermistor sensor wire looks like it was chewed on I ordered that part and will be installing it.

I'm at a loss what else it can be.
 
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Bama Rambler

Mod Squad
TFP Expert
Bronze Supporter
LifeTime Supporter
Jun 22, 2009
23,864
SouthWest Alabama
Are you seeing any error messages on the display?
Is the pressure sw light on when it's trying to light?

There are a couple of pressure switches that it looks at to make sure there is water and air flow. You can temporarily jump those out to see if it lights and runs then.
 

Paul Comi

Member
May 15, 2020
11
Southern California
Are you seeing any error messages on the display?
Is the pressure sw light on when it's trying to light?

There are a couple of pressure switches that it looks at to make sure there is water and air flow. You can temporarily jump those out to see if it lights and runs then.
Yes the pressure sw light is on.
One by one I jumped each of the pressure switches that are located on the water inlet outlet side of the filter but the heater still would not start.
 
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Paul Comi

Member
May 15, 2020
11
Southern California
I also jumped the wires that go to the gas sensor that's just before the Honeywell gas line control. It's still won't attempt to start. My gut is telling me to replace the igniter again even though it's less than two years old Because I don't see it glowing
 

Paul Comi

Member
May 15, 2020
11
Southern California
I assume you're talking about the switch that is a diaphragm and is connected to the tube that goes to the blower motor correct? I tried jumping it and nothing worked the fan wouldn't even start up but on a positive note I took a piece of 12 gauge wire that was stripped and I pulled the rubber tube off the side of the blower motor to make sure that that was clear and when I reconnected it and tried to start the heater the igniter glowed and the unit tried to start three times before giving an E05 code.
 

Paul Comi

Member
May 15, 2020
11
Southern California
E05 is igniter failed (which I'm sure you already know). Given the fact that you've tested about everything else, looks like your gut in post 5 is probably right. Time for another new igniter. :(
I installed the new pentair oem igniter and a new thermistor. The heater tried to start initially once. I tried turning off and on but the igniter didn't glow again. I allowed the heater to stay on for a half hour and when I came back it had an error E04 on the display.
 

Bama Rambler

Mod Squad
TFP Expert
Bronze Supporter
LifeTime Supporter
Jun 22, 2009
23,864
SouthWest Alabama
Since you're getting all these random things happening, I'm beginning to think the controller is the problem. You may want to have a heater guy (or Gal) look at it.
 

Paul Comi

Member
May 15, 2020
11
Southern California
I just replaced part of my gas line prior to the problems I was having and now I'm wondering if somehow I got some soil in the line. Is it possible this could cause some of these errors?
So today I figured I would try to clear out any debris that's in the furnace it's self the Jets etc. took all that stuff apart put it back together reconnected all the gas fittings and I could not get the thing to start but one thing I did notice is that when I was reconnecting everything I moved one of the I'm assuming it's a gas regulator yellow wires the lower one appears to have a section With some sort of diode in the middle that looks like it's replaceable and I sparked it by making contact with the wire and the mount that holds it what is that part and what does it do because now I can't get my heater to even turn on