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Thread: ?Need to Replace Thermostat on Water Heater

  1. #1

    Default ?Need to Replace Thermostat on Water Heater

    I have a 10 year old gas water heater. Lately the "hot water" has been only warm, and when I adjust the thermostat on the water heater to "Hotter" the heater does NOT come on until I turn it all the water to the end (where it now reads "Very Hot". ) This is new--in the past when I adjusted the temperature control the heater would fire up...
    Question: Do I need a new thermostat AND is this a DIY project... I am pretty handy.

  2. #2
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Yakima WA


    First thing I'd check is the dip tube. In the mid 90's, there major manufacturer of dip tubes for most water heater brands had quality problems and the dip tubes had a very high failure rate. Some failed sooner than other, so you may have one that failed a bit later than most. At any rate, it's easy to check. The dip tube is located in the water intake. It is usually flared and simply sets under the nipple. The tube hangs to the bottom of the tank and carries the cold incoming water to the bottom of the tank where heating occurs. Since hot water rises, the water at the outlet at the top of the tank is always hot. When the dip tube fails, the cold water mixes with the hot water at the top of the tank and cools it out so you run out of truly hot water quickly. To check the tube, turn the water intake off, relieve the pressure by opening a hot water faucet briefly, then remove the pipe on the intake on the tank. You should be able to see and feel the dip tube. Snag it and pull it out. If it is good, it will still reach the bottom of the tank. If it is bad, there will be just a short stub. Dip tubes are cheap and available at most hardware stores and plumbing shops. You may have to trim one to length. The old one is in pieces and there is nothing you can do about it. Unfortunately, the debris from the old tube will require you to clean the aerators on you sinks frequently as you can never flush all of it out of you tank...at least I haven't been able to clear mine. The only option is to replace the entire tank, but that is a rather expensive cure. Of course, if the dip tube is still intact, then the thermostat might be the next place to look.

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default temperature

    Until you know WHY the thermostat is acting that way, and it is not necessarily due to a bad thermostat, you, or we, cannot tell what to do to correct the problem. What you see as the problem could just be the symptom of some other defect.

  4. #4


    Thanks for the responses. I'm trying to check if the dip tube is intact or broken...I have an Apollo 75 gallon gas water heater; 10 years old. I turned off, and disconnected the cold water supply...and there now appears to be a fitting, with a metal "keeper" leading into the tank. Do I remove the keeper and try to back out the fitting??
    Thanks for the help--hate to replace the water heater if all it needs is a new dip tube--(Of course the owners manual does not tell me how to do this...).

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    THere are several symptoms of a bad dip tube:
    - initially normal hot water, but quickly turns tepid (the dip tube forces the incoming, replacement cold water towards the bottom, allowing the hotter water to stay at the top and provide the supply lines with hot as long as possible)
    - Often some fine white clumps in the faucet aereators and shower head - this can often disrupt the flow.

    If yours never gets hot, a bad dip tube is not the problem.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6


    The problem has been that on SOME mornings the water is hot...but on other mornings it was only tepid. This is not due to other use of hot water...shower is the first thing we use in AM. Also not due to changes in outside temperature--Now, in the last week or two....we had tepid water every AM. So I tried adjusting the temp control on the water heater to "hotter"--but the flame did not come on until I had turned the dial ALL the way to the end--then flame did light and we again have hot water.
    ? Thermostat problem...
    ? Dip Tube
    ?? Other Ideas??
    Thanks to all the folks who answered...I am pretty handy, but I need a diagnosis before I know what to fix!


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