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Thread: PacFab MiniMax Plus 400 Pool & Spa Heater – short cycling

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    PacFab MiniMax Plus 400 Pool & Spa Heater – short cycling

    I have a PacFab MiniMax Plus 400 natural gas pool heater that is giving me some issues. I am not the original home owner, but I know the system is about 12 years old. I have never used the heater very much; just occasionally to heat the spa alone. I have copies of the Operation & Installation Manual and the Service Manual. I am trying to troubleshoot and diagnose the problem in hopes that is something I can handle without bringing in a technician.

    When I try to use the system, it immediately starts cycling on and off approximately every 20 seconds. When in the “on cycle”, the status indicators lights are as follows:

    Front Control Panel (outside):
    • TSTAT – green
    • AUX. – green
    • PRESS – green
    • HEAT – green
    • POWER – green
    • SERVICE – off

    Inside Control Panel:
    • HI TEMP – green
    • TFUSE – green
    • MV – green

    When the system trips and the heater shuts off (i.e., the “off cycle”), the status indicators lights are as follows (atempted to underline the state changes on the ones that were affected):

    Front Control Panel (outside):
    • TSTAT – green
    • AUX. – green
    • PRESS – green
    • HEAT – off
    • POWER – green
    • SERVICE – red

    Inside Control Panel:
    • HI TEMP – off
    • TFUSE – off
    • MV – off

    A few other things to note that might help:

    - This quick cycling occurs independently of whether the Thermostat Selection/off switch is toggled to “POOL”, or to “SPA”. Of course, the temperature dials/potentiometers need to be turned up to start the pilot and the cycling.

    - This occurs across a wide range of pump speeds on my variable speed pump; at 1600 rpm, 2000 rpm, 3200 rpm – it doesn’t matter. I noticed that, even at 1600 rpm (what I run the pump at when I am using the salt chlorinator), the PRESS status light on the Control Panel remains lit green. I have not done any test of how low the pump needs to run at to trip the PRESS indicator off. Should I try this type of test?

    - This occurs independently of any adjustments to the bypass valve at the heater input.

    - I checked some of the wiring, and there are no obvious problems. I cleaned connectors where possible. This may need a better inspection, but I am not sure.

    - I have not attempted any further electrical trouble shooting by attaching jumpers or meters across any electrical components. There is no direction on how to do this in the manuals, so I was hoping for some directions here, if this is required.


    Here are my initial thoughts on the possible root causes, and where I am looking for the opinion of some experts.

    1. Flow Valve – I have not removed yet to inspect; I did not want to create a leak where I did not have one already. I have since bought a new gasket in preparation for possibly removing to take a look. I would assume that, if the valve is preventing water from getting to the unit, it shuts down the burner.

    QUESTION: since the PRESS indicator light remains lit through both my on and off cycles, would this indicate that the flow is not the problem? Or is this logic flawed, i.e., is it just the Pressure Switch that drive the PRESS indicator status light, or does the Flow Valve actually play here?

    2. Pressure Switch – I assume there is no problem here, as the indicator status light remains green. I have not used a jumper to actually bypass this switch. Should I? What would I expect if the switch is good/bad? Note that the outside case of the switch does show some rust. Does this component just screw in and out easily?

    3. Hi Limit Safety Switch – this is where I was heading, if the Flow Valve is diagnosed as fine based on the PRESS status light indicator. My guess would be that, if the system thinks the water is dangerously hot, it will keep shutting down the burner. That said, I am confused by one thing:

    QUESTION: there are 2 Hi Limit Safety switches; are they independent? Since I get the same symptoms whether I am using the POOL thermostat or the SPA thermostat, does this eliminate the Hi Limit Switches as the cause?

    If this is the issue, do I just go ahead and replace both – or is it possible and worth it to figure out which of the two are bad? Do these components just screw in and out easily?

    4. Thermostat Circuit Board – I guess what all else fails, blame the board. Could this be it? How do I tell?

    Any help on how to narrow this down? I would rather not sink the cash into replacing everything.

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    Quote Originally Posted by waruz

    QUESTION: since the PRESS indicator light remains lit through both my on and off cycles, would this indicate that the flow is not the problem? Or is this logic flawed, i.e., is it just the Pressure Switch that drive the PRESS indicator status light, or does the Flow Valve actually play here?This indicates that the pressure switch is sensing water flow. Good to go.

    2. Pressure Switch – I assume there is no problem here, as the indicator status light remains green. I have not used a jumper to actually bypass this switch. Should I? What would I expect if the switch is good/bad? Note that the outside case of the switch does show some rust. Does this component just screw in and out easily?Not sure why you would want to do this. Nothing indicates an issue with the pressure switch.

    3. Hi Limit Safety Switch – this is where I was heading, if the Flow Valve is diagnosed as fine based on the PRESS status light indicator. My guess would be that, if the system thinks the water is dangerously hot, it will keep shutting down the burner. That said, I am confused by one thing:

    QUESTION: there are 2 Hi Limit Safety switches; are they independent? Since I get the same symptoms whether I am using the POOL thermostat or the SPA thermostat, does this eliminate the Hi Limit Switches as the cause?Yes independent which is why there are two of them. One senses incoming water temp and the other is the outgoing water temp.

    If this is the issue, do I just go ahead and replace both – or is it possible and worth it to figure out which of the two are bad? Do these components just screw in and out easily?You can take one out at a time and see if the heater keeps running. Usually once you remove the one that is causing the issue, the unit will either keep running or refire.

    4. Thermostat Circuit Board – I guess what all else fails, blame the board. Could this be it? How do I tell?Usually the symptoms you are describing lead to be a bad limit.

    Any help on how to narrow this down? I would rather not sink the cash into replacing everything.
    See my answers in red above.

    Now even though a limit is relatively cheap, consider the condition of the rest of the unit. Are the burners in good shape, any rusted holes anywhere in the unit etc. The main thing being that the unit is not a fire hazard.
    Paul
    http://www.gastekservices.com A word of caution: When working with gas and electrical you might want to consider a licensed contractor. Consider the value of your life and others around you. If you would like to provide a review of the help I provided, please use the following link to leave a review. gastek - Google Search,

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    Thanks Paul.

    Based on this, I put a jumper across the two wires from the board to bypass both Hi Limit switches, and the system stayed on and stopped cycling. I attempted to bypass the two switches one at at time to isolate which one was bad, but both times the system went back to cycling on/off. Does that indicate that both switches are bad? Or, is it likely that I did not correctly isolate each one seperately (i.e., did not place the jumper in the right locations)? How do you isolate the individual switches?

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    Quote Originally Posted by waruz
    Thanks Paul.

    Based on this, I put a jumper across the two wires from the board to bypass both Hi Limit switches, and the system stayed on and stopped cycling. I attempted to bypass the two switches one at at time to isolate which one was bad, but both times the system went back to cycling on/off. Does that indicate that both switches are bad? Or, is it likely that I did not correctly isolate each one seperately (i.e., did not place the jumper in the right locations)? How do you isolate the individual switches?
    You will need to find each switch. Disconnnect the wires to it and hook them together
    Unknown make 18' above ground (bought used in 1999) Sparco sand filter. Hayward 100,000 BTu heater. 2 speed pump

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    The way I do it is I pull each limit switch out of their hole one at a time and then see if the heater fires. Pulling them like that allows it to cool down thus allowing the unit to fire. You could also make up a jumper with a spade clip on each end and then pull one of the limits and put a jumper in its place.
    Paul
    http://www.gastekservices.com A word of caution: When working with gas and electrical you might want to consider a licensed contractor. Consider the value of your life and others around you. If you would like to provide a review of the help I provided, please use the following link to leave a review. gastek - Google Search,

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    Paul, Danpik,

    A Pentair tech suggested that, if my jumper test wasn’t performed properly, the unit would not have lit at all and that it is unlikely that both hi limits would have failed simultaneously causing the unit to trip prematury. He suggested that the flow valve assembly might be worn or corroded, causing the water to overhead - thus tripping the (good) hi limit switches. He suggested that I remove, inspect, and test the power element section by submerging it water exceeding 130 degrees and seeing if the unit expands.

    Based on the symptons and the other tests I performed, does this make sense? If the flow flave was creating an issue and the water overheated, wouldn't the system trip off and stay off as opposed to cycling on/off every 20 seconds? How about the diagnostic lights - would the PRESS light trip off?

    Any thoughts on this suggestion?

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    I don't have intricate knowledge of that particular heater. With that said, this I do know. limit switches are nothing more than a "make/break" type of switch. The circuit will either be Open or Closed depending on the condition it sees. Open meaning there is a break in the electic flow. If the switch is open it is just the same as one or both wires being off of the terminals. If you put a jumper between the wires then the circuit (switch) will be closed and electric will flow. If you test each limit switch individually this way and the condition does not clear up then bypass both at the same time. (Could be both are acting up...unlikely though). If doing this does not clear the problem I would then jumper the flow switch. I attached a marked up shot of the schematic



    In this, the yellow is the incoming power from the transformer (this is all low voltage) Where I switched to red (i think it is red, as I am colorblind) is the circuit you want to test out. As you can see each one of these switches is simply daisy chained to each other. If one fails then the circuit will not complete. Where I put the black "X" is the wire that goes thru a fuse, back to the board and then to the gas valve. I think you will find you problem to be somewhere in one of the three switches in that circuit.

    There is also one other remotely posible situation...Several years ago, my heater would cut out after 2-3 min of running. I jumped out everything... limits, flow switches, thermostats, etc. I literaly had the gas valve powered right from the transformer outputs from the board. Still had the same problem. Here is the hitch though. I could not get it to repeat the problem with the lid off of the heater. Thinking bad board, I dreaded the thought of paying $400.00 for a replacement as the heater only cost me $600. I pulled the board and took it to work to show it to my electrical engineer buddy and see what he thought. Thinking it was a bad relay on the board I started to look up the replacements as he was looking it over. After a min of looking at it he pulled out a magnifying lense and found the problem. All of the conections for the oncoming power plug were poorly soldered from the factory and had cracks around them. This explained the problem I was having and why it would not repeat when the cover was off. Heat buildup inside the enclosure would cause just enough expansion to break the circuit on the board, but would not get hot enough to do it when the cover was off.
    Unknown make 18' above ground (bought used in 1999) Sparco sand filter. Hayward 100,000 BTu heater. 2 speed pump

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    Quote Originally Posted by waruz
    Paul, Danpik,

    A Pentair tech suggested that, if my jumper test wasn’t performed properly, the unit would not have lit at all and that it is unlikely that both hi limits would have failed simultaneously causing the unit to trip prematury. He suggested that the flow valve assembly might be worn or corroded, causing the water to overhead - thus tripping the (good) hi limit switches. He suggested that I remove, inspect, and test the power element section by submerging it water exceeding 130 degrees and seeing if the unit expands.

    Based on the symptons and the other tests I performed, does this make sense? If the flow flave was creating an issue and the water overheated, wouldn't the system trip off and stay off as opposed to cycling on/off every 20 seconds? How about the diagnostic lights - would the PRESS light trip off?

    Any thoughts on this suggestion?
    The power element is a pretty easy test to do. In fact most times just visually looking at it will show you that its bad. Unbolt it from the unit and slide it out. If it's all corroded up, then that could be your issue. So remove it and see what you find.
    Paul
    http://www.gastekservices.com A word of caution: When working with gas and electrical you might want to consider a licensed contractor. Consider the value of your life and others around you. If you would like to provide a review of the help I provided, please use the following link to leave a review. gastek - Google Search,

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    Paul,

    How is the Flow Valve / Power Element removed for inspection? I removed the two bolts, but could not budge the cap to slide it out (I had bought a new gasket in case the existing one got damaged). Is there a special technique or tool required? I tried to pry it a bit, but backed off - I did not want to damage anything without checking in first. Photo attached.
    Attached Images Attached Images

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    It should just slide out unless the spring has broken and lodged inside somehow. Try twisting it and pulling at the same time. It should pull right out.
    Paul
    http://www.gastekservices.com A word of caution: When working with gas and electrical you might want to consider a licensed contractor. Consider the value of your life and others around you. If you would like to provide a review of the help I provided, please use the following link to leave a review. gastek - Google Search,

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    Thanks. I was able to get a pair of vice-grips on it and get the valve out. It did not look terrible in terms of corrosion (photos attached). I noticed that the power element "tip" was not threaded all the way in and, as a result, the distance between the exterior cap and the plate between the two springs was 3 7/8" (off by 1/8" according to the drawing in the maintenance manual - see attached photo).

    I did thread the power element all the way in and cleaned it up a bit. I doid notice that the smaller spring was a bit contorted, but all the mecahnisms seem to move. I tried to test the valve and element in alternating hot/cold water, but it was difficult to tell if it was moving at all. How much should the element extend and compress the spring? More than 1/8"?

    Take a look at the photos and let me know what you think. This is wearing me down and I am now considering just buying a new valve and two limit switches. I did talk to someone on the phone and they instructed me to buy the less expensive "standard" flow valve, as the ASME version should have only been used in commercial application - which mine is not. Do you agree? I also removed the two Hi Limit Safety switches and tested continuity across the leads; they looked ok.

    Mike
    Attached Images Attached Images

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    Re: PacFab MiniMax Plus 400 Pool & Spa Heater – short cyclin

    Looks can be deceiving. On something like this I would have to just try a new one and see if that resolved the issue. The spring looks OK to me as they are contorted like that most of the time when I see them.
    Paul
    http://www.gastekservices.com A word of caution: When working with gas and electrical you might want to consider a licensed contractor. Consider the value of your life and others around you. If you would like to provide a review of the help I provided, please use the following link to leave a review. gastek - Google Search,

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