Pentair MiniMax 400 cycling - noob needs help please

Jump to latest Follow Reply
S

spydermike

0
Feb 2, 2017
21
Lake Forest, CA
I am new to pools, so please bear with me. I have kept my above ground spas working with various repairs over the years. I just bought a house and I like to understand how things work. I have the Pentair MiniMax Pro 400 gas heater that turns on fine and starts to heat - all lights on the panel are green, and then, after a short while, just the heater light goes out and it cycles in somewhat random timing but all within a minute of each other. It turns on then runs then shuts down...the service light does not come on. All other lights stay green.

The previous owner had recently installed a Pentair variable speed pump and runs it mostly in low speed (2,000rpm) for cleaning. They never heated to pool, just the spa. Could the flow detection be looking for a higher rate of flow? It seems I would see the PRESS light go out if that were the case.

Where is the best place to start? I am okay with multimeters. Hi Limit Switch? Some thermal regulator?

Looking for guidance please.

Thanks,
Mike
 
Is the filter clean? No error codes on the display, just cycling? Have you tried bumping the speed up on the pump? Cycling is usually an indication of it overheating which can be water flow.
 
I have experienced this issue with my heater several times. It always turns out that the burners need to be cleaned. The gas flows well enough to start but due to dirt and soot on the burners the volume of gas is not enough and it cuts off after a short amount of time only to try again a bit later to repeat the cycle.

I recommend removing and cleaning the burner assembly.

Here is a link to my initial post a couple years ago about cleaning the burner assembly.

Cleaning Pool Heater
 
My first time it took me about 1 hour to take apart and about 30 minutes to clean and than another 30 to re-assemble. Now I can take it apart in about 10 and put together in 10. I still think dealing with the gas line was the most difficult part of it. Make sure to check the gas line for any leaks once you turn it back on. Also wait about 5 minutes or more after turning the gas back on before firing the unit on.
 
I believe mine is about 15 years old. It is the thing I am most nervous about every time I open the pool, however it still works. So far all my issues have been due to the unit being dirty. If I clean the unit correctly before trying to turn it on it works great. I have a 25,000 gallon pool and a 400,000 BTU heater and it will heat the water from the mid 70s to the 90s in about 8 to 10 hours.

It is the only heater I have experience with but will be happy to have a new one when I get one, simply for the ease of mind due to my current one being so old.
 
Rocco said:
I believe mine is about 15 years old. It is the thing I am most nervous about every time I open the pool, however it still works. So far all my issues have been due to the unit being dirty. If I clean the unit correctly before trying to turn it on it works great. I have a 25,000 gallon pool and a 400,000 BTU heater and it will heat the water from the mid 70s to the 90s in about 8 to 10 hours.

It is the only heater I have experience with but will be happy to have a new one when I get one, simply for the ease of mind due to my current one being so old.
Click to expand...
Rocco - that is a very good testimony for the MiniMax. 15 years is pretty darn good in my book. I'd expect to have to clean it every few seasons. Thanks for the information.
 

Enjoying this content?

Support TFP with a donation.

Give Support
mac4lyfe said:
I'm thinking about purchasing a Minimax 400. Thoughts? I hear a lot of good things about Raypaks but I can probably get the Minimax discounted 60%.
Click to expand...

If you are purchasing a new unit, get the Raypak. Beware of used heaters as you get what you get. The Minimax is an old unit and has been replaced by others that are not as good.
 
To close out this thread, I downloaded the ops manual and the service manual. I opened up the unit and checked the burner operation - all burners were a nice blue flame. I checked the back of the control board and notice when it cycled that all three LEDs went out. The hi-temp limit switches are first in the circuit, so I went to check them. I had forgotten my meter so I removed the jumper between the sensors, picked on and operated just on that one. I must have picked the correct one as the heater fired up and worked for several minutes (instead of less than a minute).

I noticed it started to cycle again. I drove back to my other house and grabbed the meter and a jumper. Testing the sensors with a meter showed the one I bypassed was solid open. The other one would start to open up after the water started warming. I bypassed both with the jumper and the heater worked as it should - no cycling.

I have two new sensors on order. It looks pretty simple - do they just screw in by hand? There are no flats for a wrench.

Mike
 
There are 2 high limit switches. One opens at 135 F and the other opens at 150 F.

Definitely do not operate the heater like it is. You probably have very little flow, which can cause the water to get super hot.

It can also ruin the heat exchanger.
 
I am not sure you read my information - one sensor reads open circuit at ambient and stayed there - it was failed open. The other sensor would fail open before the heater warmed the water up very much. The service manual shows two limit switches with the same part number - they are both 150 degree P/N 071017.

I have not operated the unit without them only to test/troubleshoot. If, after sensor replacement, it continues to cycle, then I continue troubleshooting.

Thanks,
Mike
 
It could be bad high limit switches, a bad flow valve, low flow due to low rpm or maybe a scaled exchanger.

You need at least 40 gpm for that heater. Probably want to target about 50 to 60 gpm for good performance.
 
Just adding a bit more info to the story here. I changed out the temp sensors and after a couple of minutes it started short cycling again. I pulled the flow valve (real easy to do) and checked it out. It only opens about 1/8" in real hot water. The copper end unit seemed a bit bent and out of alignment. I have a new on coming in to try out.
 
I received the flow valve and tested both in a pot of water. The old one took forever to open about 1/8", the new one responded much more quickly and opened about 1/2" before I shut down the experiment. I will install it once the rain stops in a day or two and post up the results.
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply