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Thread: MasterTemp400 Cycling ON/OFF

  1. Back To Top    #1

    Join Date
    Oct 2015
    Location
    Dallas
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    3

    MasterTemp400 Cycling ON/OFF

    Hi all,
    I bought my first house this spring, along with it came my first pool and spa (both in-ground).

    To make a long story short, I'm having trouble with my Pentair MasterTemp 400 heater. Originally when we bought the house the spa seemed to work fine (from my limited knowledge of spas).

    In the last 2-3 months or so the spa heater has been cycling on and off. The Heater itself remains on, but it cycles off the heating unit, so it is blowing cold water thru the jets, then the heater turns on again and pushes hot again. Obviously this makes the spa take a very long time to heat up, and unpleasant when the cold water is blowing.

    After some research, I bought and installed a new Thermal Regulator.
    Amazon.com : Pentair 77707-0010 Thermal Regulator Replacement Kit Pool and Spa Heater : Portable Outdoor Heating : Patio, Lawn Garden

    And it seems to have helped. The off cycles of the heating unit in the Heater are shorter, about 30sec-1min. But they still happen.

    What would my next step be in trouble shooting this?


    (The original Thermal Regulator was very corroded. I have no idea how long it had been in use, but it had a thick patina of green oxidation on it.)

  2. Back To Top    #2

    In the Industry

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    Jun 2015
    Location
    Wildomar, California
    Posts
    423

    Re: MasterTemp400 Cycling ON/OFF

    Here's the check list; thermal regular, internal bypass, dirty filter, low flow problems, damaged igniter, hi limit switch, pressure switch fan or fan switch, lined up or leaking heat exchanger. Long list, but filter, flow, or internal bypass are your best bets to look at since you already did the regulator.

  3. Back To Top    #3

    Join Date
    Oct 2015
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    Dallas
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    Re: MasterTemp400 Cycling ON/OFF

    OK so I had another look at it today.

    I tested the new Thermal Regulator that I installed last week by holding it over the exhaust of the heater while the heater was running. The regulator seems to work (the pokey-out bit poked out).

    The heater DID cycle off while it was running with the Thermal Regulator was removed, so I guess that it was not the problem. (Old one looked pretty bad).

    I noticed that the needle on the Pressure Gauge on the filter was moving back and forth between 20-32psi when the heater clicked off. So I suspect that the pressure switch is what may be kicking the heater off...which means its working and the problem is caused by a faulty Internal Bypass?

    Is there a way to check this without replacing it? Is it difficult to replace or can I do it myself?

    Edit: Also, I saw no LED's under the control board lit up, so I don't believe there is any sensor issues.

  4. Back To Top    #4

    In the Industry

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    Jun 2015
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    Wildomar, California
    Posts
    423

    Re: MasterTemp400 Cycling ON/OFF

    You have to visibly inspect the internal bypass, which means taking the manifold off. It's not hard, it just takes time and patience. Are you there are no flow issues?

  5. Back To Top    #5

    Join Date
    Oct 2015
    Location
    Dallas
    Posts
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    Re: MasterTemp400 Cycling ON/OFF

    OK, I will remove the manifold and expect the Bypass valve this weekend.

    The pump itself seems to be running normally when the heater is turned off. The filter was cleaned about 3 months ago, and skimmers are emptied on a regular basis. When I tested this yesterday, I was adding water too the pool, but it wasn't low, and none of my pipes seem to be leaking. So I would suspect that the flow should be fine, but I'm not sure how to check that other than putting my hand in front of a jet. (I'm still learning, so if there is a way to check this, please tell.)

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