Pentair Minimax 400 CH heater cycling and not very warm

[david714]

Hi everyone,

I have a spa with a Pantair Minimax 400 CH heater, 2HP filter pump, 60sq. ft. DE filter and Jandy aqualink controls. I noticed that spa takes a long time to heat up because my heater turns off then back on every few minutes. The temp on the Jandy is set to 100F, but the heater cycles a lot before getting anywhere near this temp.

The heater has 4 LEDs on the front that should all be on when it's heating. Every few minutes, the flames go out and the bottom LED labeld "Heat" turns off. The other 3 LEDs stay lit, the service light is always off, and the 3 LEDs hidden on the back of the controller board are also always lit. After a few minutes the heat LED comes back on and it starts heating again. What could be causing my heater to turn on and off every few minutes? Also the water on the output side is not really that hot. I bought the home with this already in place so I can't compare the performance of the heater to how it was on day 1.

thanks in advance
David

 

[ps0303]

There can be several things causing this but my first guess would be the limits. Have you opened the front of the unit to see what the condition inside of it is? Almost every single one of these units I come up on are rusted out totally inside and aren't worth putting a penny into it. Plus they are a fire hazard as well once they rust out. I would open it up and see what things look like before any further diagnosing.

 

[david714]

I did open the front, the burners look ok, flames seem good and strong. I could not see the heat exchanger. What are the limits? I assume you mean a high temp limit and a low flow limit... If one of these limits were causing the shutoff, wouldn't that cause one of the 3 LEDs on the back of the controller board to turn off? Thanks for the reply, I'll be careful

The unit does have some rust, mostly near the bottom...

 

[ps0303]

As you stand in front of the heater, take the right side panel off. It has two screws holding it on. Inside there you will find two limits and the pressure switch. Starting with the one nearest the pressure switch, you can try and jump it out. Meaning remove the two wires connected to it and then connect them together with another wire. Now see what happens when you turn it on. If the cycling stops, you found your problem. Replace the limit with a new one, while the pump is turned off.

BTW, if you can see the concrete pad under the heater from the inside, that means the bottom is rusted out and then you really should replace the unit. An open bottom is a fire hazard.

Also, here a link to a repair manual for this unit.

https://www.parts4heating.com/v/vspfile ... iMaxCH.pdf

 

[david714]

Hi Paul,

Thanks for that detailed reply. Last night I waited for the heater to cycle off and I did what you suggested. I removed one of the wires from the top limit switch and I was about to jump it to the other wire to close the circuit. As soon as I removed it I noticed that the 3 LEDs on the back of the controller board turned off. This makes me think that the circuit was closed before I removed the wire form the limit switch. Jumping the wire and bypassing the limit switch causes the 3 LEDs to turn back on, but the flames don't come back on right away. I suspect that there is some sort of time delay before the burners turn on again... I also checked the pressure switch and saw the same thing. As soon as I removed a wire from the switch the "Pres" LED of the front of the unit turned off indicating that the circuit was closed before I pulled the wire.

Should the flames come right back on the moment the limit or pressure switch closes or is there a delay? If there is a delay then I think even a momentary break in the switch could be causing the cycling. If there is a momentary break in one of the switches then the switch may already be closed by the time I examine it.

I'm also attaching some pics of my unit.

thanks
David