Pacfab Minimax Plus 400 heater is short cycling

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bgrinstein

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Mar 8, 2012
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My Pacfab Minimax Plus 400 heater is short cycling (turning on and off rapidly). The troubleshooting section in the manual suggests the problem/remedy may be one of the following:

1. insufficient water flow/clean filter
2. defective wiring/repair or replace wiring
3. defective flow valve or out of adjustment/call serviceman
4. defective hi-limit and-or thermostat/call serviceman

My question is really how to narrow down the above possibilities (ok, I am sure the problem is not low flow)? Obviously I do not want to call a serviceman again, but I am quite adept with electronics (less so with plumbing).

Here are some thoughts, please tell me if this makes sense:

1. Wiring does not go bad after 15years of operation. So it seems to me #2 above is unlikely
2. Short cycling occurs with switch set to either "pool" or "spa." Since each of those has a separate hi-limit, it is unlikely that both hi-limit shut offs went bad simultaneously. So it must not be the hi-limits.

If this is good logic (is it?) then I have to decide which should be the first step: replacing the thermostat board (easy to do, part is $120) or replacing/adjusting the flow valve (no idea how to do, probably difficult, about same price as thermostat).

Last question: how does one adjust the flow valve?

Thanks!
 
Yes,I have a copy of the manual.

Light indicators: this is weird, I went out to look at them after I read your post and now I got (for the first time) the heater won;t come up at all. As I tried this by turning on the SPA from my remote(Easytouch) while the pump was in the cleaning cycle, I am unsure how to interpret the result (problem in control electronics or in heater?). In any case, I will try it again when the cleaning cycle is over.
 
Does the power light come on? If it does, I'd suggest checking the rocker switch (pool/spa) to see if it might be the problem. If you are not getting the power light to come on when the EasyTouch switches it on, I would suggest the following:

1. Make sure the heater is actually getting power and there is no breaker down.
2. Some older units have a breaker associated, so check to see that the internal breaker for the transformer has not popped.
3. Check transformer output with a multimeter. Compare with service manual.

If the transformer works, but you are still not getting the power light, I'd suspect faulty wiring/connectors to the control PCB.
 
Let me add to previous: 1. I noticed the power light is always on, regardless of state of Easytouch. 2. I opened the panel and bridged the rocker switch: the power light stayed on and the heater did not start.
 
bgrinstein, any luck on this?

Mine just started doing the same thing this week after working great all year - short cycling with the switch set to pool or spa and the thermostats at their normal positions. Then if I turned the switch off and then back to pool/spa it wouldn't come on at all (seems like what you saw). Water flow is normal and gas flame is blue. Service light is only on during ignition, as it should be, and the rest of the lights are on as usual for the short period the heater is running. Strange thing is if I turn either of the thermostats to max the heater will turn on again and stay on (haven't tested how long yet) and then if I move them slightly from max the heater will turn off - definitely not normal operation.

Hard to believe both thermostats / sensors would go bad at once, so I'm suspecting the board or probably something really obvious I'm missing. Next step is to break it open and take a look. If I still can't find anything I'll give Pentair a call. Would appreciate hearing if you found a resolution to your issue.
 
A couple of things, IIRC, there's one sensor, the thermostats merely set a temp for pool or spa mode.

Additionally (going back to the original post) there are two hi-limit switches, however they have nothing to do with the mode (pool/spa) they detect hi temps on the inlet and outlet side of the heat exchanger, and are there to protect the heater.

All that said, (CraigMW) I would suspect the temp sensor, however, by all means contact Pentair, I've found their support to be excellent
 
Dear Qwaxalot:
Here is what I got from Pentair's support, after one week wait to hear form them:

"The problem could be upstream somewhere in the safety loop. Was the heater showing a water temperature? Did the fan motor turn on and blow cold air out the side?"

To which I replied:
"I am confused about your question "Was the heater showing a water temperature?" The heater does not have a display that gives temperatures. Maybe you could clarify? As for `Did the fan motor turn on and blow cold air out the side?' the answer is no. When I turn on the SPA from the easytouch (which is set to turn on the heater) or when I turn the heater manually (by disconnecting and then jumping the pins for external control in the circuit board, and turning manually on) I get nothing: no apparent response whatsoever."

Which elicited a response: "How old is the heater? And what model do you have?"

This being answered, I never heard from Pentair again.
 

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lewis291 said:
bgrinstein, any luck on this?

Mine just started doing the same thing this week after working great all year - short cycling with the switch set to pool or spa and the thermostats at their normal positions. Then if I turned the switch off and then back to pool/spa it wouldn't come on at all (seems like what you saw). Water flow is normal and gas flame is blue. Service light is only on during ignition, as it should be, and the rest of the lights are on as usual for the short period the heater is running. Strange thing is if I turn either of the thermostats to max the heater will turn on again and stay on (haven't tested how long yet) and then if I move them slightly from max the heater will turn off - definitely not normal operation.

Hard to believe both thermostats / sensors would go bad at once, so I'm suspecting the board or probably something really obvious I'm missing. Next step is to break it open and take a look. If I still can't find anything I'll give Pentair a call. Would appreciate hearing if you found a resolution to your issue.
Click to expand...

As you can tell from my reply to Qwaxalot, the answer is no. I do have to add that the progression to where I am now is precisely how you describe it for yours (including the behavior of warning lights and of moving the dials slightly form max and the heat turning off, among others).
 
You should search for the manual on the web. The service manual describes potential faults and how the LEDs on the controller board report these. This would be the best way to go to find out what's wrong. It sounds like Pentair's service people were pretty useless (asking about a fan and temp. display on a MiniMax???). I hope I don't encounter this, as our system is now pretty much all Pentair.
 
I have some success to report, I hope this is useful to others. After I finally got a hold of the actual SERVICE manual (as opposed to the Operations and Installation Manual) many things became transparent. There are clear step by step troubleshooting instructions. It took me 10 sec to determine the problem with the heater not turning on was the circuit board. I replaced the board and presto, back to where I started with a rapid cycling heater.

For this, the service manual basically says check for flow. If the flow is good, check the flow valve. I took out the flow valve (which is surprisingly easy because it is readily accessible and held in place only by two bolts). Here is a picture showing rust buildup welding the post to the assembly, rendering the valve nonoperational.

[attachment=0:359pi2uw]IMG_9596.JPG[/attachment:359pi2uw]

I have ordered a new one and have no doubt this will fix my rapid-cycling.

Thank you CraigMW!!!
 

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I bought a home a couple years ago and it came with an in-ground spa with a Minimax 400 Plus heater. Owning this has been like owning an old car. Every time I fix one thing, something else breaks!

It started with gas line that took on water due to corrosion. I suspect the water in the line ruined the gas valve in the Minimax. Had new gas line installed and replaced that part. Then the heater seemed good for a year. The temperature knobs slowly became erratic. I eventually had to use the pool side because the spa side was only about 80 degrees when turned to max, and after a while, it just stopped working altogether. I replaced the control board because I figured the pool side would suffer the same fate soon.

Next, the water pressure sensor crapped out. That one is pretty obvious (T. Pres display on the front).

Now, the heater works up to 90 degrees or so, then starts short cycling. I temporarily bypassed the hi limit sensors to confirm that those are what are causing it to cut out. Tried replacing them but no luck. Then I found this thread. Flow valve, eh? I found it and pulled it out today. Mine looks exactly like bgrinstein's, perhaps a little worse. There are holes in the copper nub at the end. Part is on order and I'm sure it will solve this issue.

I wonder how much longer the heat exchanger is going to last. :)
 
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