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Hot water heater no longer produces enough hot water. Why?

Joseph_4 Member Posts: 271
Assuming the dip tube is intact in a regular gas fired water heater and the thermostat is not faulty, why would someone complain they just aren't getting as much hot water as they used to? Or what can cause this problem?


  • Timco
    Timco Member Posts: 3,040
    water temps

    What is the incoming water temp? What is the GPM of the demand (shower head)? Use a 5 gal bucket and at the tub spout measure what you are really getting. Deposits on tank bottom is another issue. Maybe the stat is getting a false reading of actual water temp?
    Just a guy running some pipes.
  • Joseph_4
    Joseph_4 Member Posts: 271
    checked water temps

    thermostat set for 145, put thermometer in water at sink   it measured 135. think that makes sense because of heat lost travelling through pipe to get to sink
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,294
    Other things...

    ... that can cause trouble are cross connections in the piping or a recirc line that doesn't have a working check valve.  An easy test for cross connections is to turn the cold supply to the heater off and open a hot tap.  It should stop running right away. 

    You should get 70 to 75% of the volume of the tank as undiluted hot water.  Get out a bucket and stop watch to measure flow in the shower particularly.

    See if the heater fires much with no use.  There may be a pipe leak hidden under a slab or some sneaky such.

    Yours,  Larry
  • Tim McElwain
    Tim McElwain Member Posts: 4,621
    edited April 2010
    Are there any mixing

    controls that are inadvertently mixing when they should not? The first place this usually happens is at the washing machine when both hot and cold lines are left on at all times.


    Whoops I just read Larry's post I think we are both talking about the same thing.
  • EricAune
    EricAune Member Posts: 432
    I'm with Larry on this one

    After checking for scale build-up on the bottom of the tank I would check for any possible cross-connection. 

    What type of shower control valves do you have?  Cross-connection is fairly common between hot and cold in most Moen valves.  The problem is usually fixed with the replacement of the valve cartridge, however the balancing portions may need adjusted or replaced also.
    "If you don't like change, your going to like irrelevance even less"
  • Alan (California Radiant) Forbes
    Reduced Output

    I think I've heard of that symptom ever since I started plumbing.

    If it were a cross-connection problem, you wouldn't be able to get any hot water.

    If it were a scale build-up, that just makes the water heater take longer to reach setpoint, no?  Unless the scale takes up a quarter or more of the tank bottom.

    To me, it's always been a mystery.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Tim McElwain
    Tim McElwain Member Posts: 4,621
    Alan I have had numerous cases that

    were caused by the mixing control on the washing machine. The water in the shower would start hot and then suddenly reduce in temperature I was never sure exactly how it did this but shutting off the feed to the washing machine solved the problem.

    In many of these the washing machine was in the basement very close to the shower involved on the next floor or is some cases two floors up but directly above the washing machine location.
  • Slimpickins
    Slimpickins Member Posts: 339
    Gas control

    I had a service call with the same problem and determined it was the gas control. I removed it from the water heater and the sensing element is wrapped in plastic with the end open to sense the water temp. In the open end it was full of debris, little rocks and stuff. I cleaned the stuff out and reinstalled the gas control and it's worked fine ever since.  
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