Runaway Thermostat?

Discussion in 'Water Heater Forum, Tanks' started by PM5K, Nov 25, 2013.

  1. PM5K

    PM5K Member

    Oct 9, 2006
    San Antonio, TX
    Relief valve opened on my hot water heater. The water was very hot from the tap, so I turned the unit off and ran enough water through it to get cold water into it. I checked the valve to make sure it was working properly, and then tried to turn the unit back on, however it would not turn on. I reset the breaker on the thermostat and it came back on.

    So it seems to me I have a runaway thermostat.

    This is just a point of use Ariston 4 gallon water heater, just want to be sure before I go pick up a thermostat, because I suppose it could also be the element.


    (Also it's just a small point of use unit so it's off until I get it fixed)
    Last edited by a moderator: Nov 25, 2013
  2. Raspy

    Raspy New Member

    Dec 22, 2013
    Radiant heating contractor
    Northern Nevada
    The element only responds to the thermostat and cannot make the water heater "run away"
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  4. WyrTwister

    WyrTwister New Member

    Feb 12, 2014
    Lubbock, Texas
    The tstat only switched one of the two hots ( 240 VAC ) I saw a WH that had an element shorted to ground on the un-switched hot . Therefore , part os the element was apparently running / heating 24/7 ?

    The big box stores carry a plumbers pack with upper and lower tstat and 2 elements . That might be the way to go ?

    However , if yours is a 4 gallon unit , is it 120 VAC ?

    God bless
  5. DonL

    DonL Jack of all trades Master of one

    Mar 30, 2011
    Rocket Scientist
    Houston, TX
    I agree that a shorted element can cause the problem.

    If they short they can weld the contacts on the thermostat.

    Is that unit on 120V or 240V ?

    Good Luck.
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