Pentair MiniMax Heater Won't Ignite

[Moragan]

Greetings - I'm seeking ideas to help diagnose why my Pentair MiniMax NT-STD-N Heater Won't Ignite. Background:

• Heater was idle without power for a couple of months. It is 15 years old.
• It will go through the normal start-up sequence. Power on, Thermostat lit, Heating lit (very briefly).
• Makes the noises I expect (blower on and clicking). Excepted is the noise of the gas burners igniting.
• Heating light turns off within 1 - 2 seconds. Smell a small amount of gas.
• System recycles two more times and then simply blows air.
• The digital read-out does not give an error message (no E05).

What I have done so far:

• Confirmed that the surface ignitor is getting 120 volts, and glows orange. Pulled it and no sign of damage.
• Pulled the flame sensor and no sign of damage and just lite surface oxidation.
• General inspection shows no soot and limited rust.

I have replaced the pressure switch a couple of times, but no other significant maintenance has been required.

Appreciate any suggestions, including how to test functionality of the flame sensor and ignition module.

 

[danpik]

Did you clean the flame sensor? These work on a milivolt level and any oxidation/corrosion/dirt/ etc will cause them to not work. The best way to clean these is to "polish" them with a crisp $1 bill. Fold it a couple times, wrap it around the probe an "sand" away. The symptoms you expressed indicate a dirty flame rod.

Also, unplug and plug the flame rod wire connections a couple of times to "clean" the terminals

Dan

 

[Rocco]

I have the same type of unit and have had the same issue multiple times. I have had to remove the burner assembly and clean it off when I open in the spring. During the winter some soot or other debris will collect on the burner assembly limiting the gas and as a result the unit will turn off, try a couple of times, and then turn off for good.

The burner assembly is fairly easy to remove once you get the gas line off. Here is a link to a thread I started in 2014 about this issue. Let me know if you have any questions.

Cleaning Pool Heater

 

[Moragan]

Danpik and Rocco - Many thanks for your help. I wish that the quick and easy fix of removing oxidation from the flame sensor had worked. Will do a bit more diagnosing, and then will pull burners for cleaning. If in the burners, likely an insect issue. I really see no evidence of soot.

 

[KDpoolguy]

Try checking the ground. If there’s oxidation or the ground wire isn’t getting a good connection, it could cycle like you mention.

 

[txgunlover]

I went through the same thing with my 16 year old minimax 400 last year... replaced almost all parts, control board, etc... finally replace the whole unit...