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Thread: Pentair Mastertemp 400 displaying wrong temp - Lesson Learned and shared.

  1. Back To Top    #1

    Join Date
    Sep 2010
    Location
    Yorba Linda, CA
    Posts
    5

    Pentair Mastertemp 400 displaying wrong temp - Lesson Learned and shared.

    I have had intermittent issues with my 3yr old Pentair Mastertemp 400. It would occasionally show a temp that was much higher than the actual water temp. If the pool water was say 65D the heater would show a water temp of 115D. After a couple of hours the temp on the heater would correct itself. But because it was reading a temp so high, it wouldnít fire the burner. Very annoying! I replaced the thermistor, but this didnít resolve the issue.

    After some tinkering (and goolgling) I found the answer:-

    I would bleed air out of the Clean & Clear plus filet by opening the manual relief valve on top. This would release the air from the top of the filter and then a jet of water under pressure as all the air is expelled. This jet of water is directed at the heater and was getting the heater manifold wet, as well as the water flow sensor and Thermistor connections. I remove the side panel from the heater and dried the connections. This improved the accuracy of the heater temp display. I then ran a hair dryer on the connections while the heater was on. Hey presto, the numbers dropped to the correct values in 15 seconds!

    So if your Pentair Mastertemp is showing the wrong temp, try not getting it wet!
    15000 Gals, Catridge, IG, plaster, intelliflo VS-3050

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    Patrick_B's Avatar
    Join Date
    Jun 2011
    Location
    Midland TX
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    15,001

    Re: Pentair Mastertemp 400 displaying wrong temp - Lesson Learned and shared.

    Hmmm, good to know....

    Maybe it will help someone out do the line. Thanks for passing it on.
    TFP Moderator
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    28K Gal IG FreeForm, CLI Quartz, Pentair 36"SF & VS Pump, Dolphin M5, Rheem

  3. Back To Top    #3

    Re: Pentair Mastertemp 400 displaying wrong temp - Lesson Learned and shared.

    This worked for me. I had the same issue! Thank You for your help. I used my electric leaf blower instead😜 I have the pentair master temp 300.

  4. Back To Top    #4

    Join Date
    Jul 2017
    Location
    Ottawa ON
    Posts
    1

    Re: Pentair Mastertemp 400 displaying wrong temp - Lesson Learned and shared.

    Same thing just happened to me with a Mastertemp 250.
    I had opened it to replace the igniter - which was very easy to do. After starting it up though, the temperature was super low. Read 44F when the water was 68F. Then it turned off when the temp read 120F. It has been raining here like crazy the past few days so things were pretty damp inside it.
    Opened it up an blew it dry with a hair dryer. Only once I blew air above the control board on the lid (careful not to get it too hot) did the temperature drop to give a correct reading.
    Turns out there was a garter snake hiding above the control board so he must have shorted it out.
    Anyway, everything is good now! Thanks!

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