Runaway Thermostat?

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

  1. PM5K

    PM5K New Member

    Messages:
    154
    Location:
    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.

    Thanks!

    (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

    Messages:
    11
    Location:
    Northern Nevada
    The element only responds to the thermostat and cannot make the water heater "run away"
  3. WyrTwister

    WyrTwister New Member

    Messages:
    6
    Location:
    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
    Wyr
  4. DonL

    DonL Jack of all trades

    Messages:
    3,820
    Location:
    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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