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I have a 50 gallon gas water heater that's just under 10 years old. We're getting inconsistent water temps out of it - last night filling up a bath I had the tap all the way hot and it was barely warm enough for the kids bath (wouldn't have been near hot enough for an adult). Other times I have to substantially open the cold to temper the water down to a good bath temperature. This is at the same time of day, with the same usage earlier (none for >8 hours), so it should be about the same. It affects all outlets, not specific to one bath or shower.

It's a Kenmore Power Miser 9. The burner appears to cycle normally - we hear it kick on after taking a shower or using significant hot water.

I flushed it a few weeks ago using the drain valve with no change. The flushed water looked clear, it wasn't obviously full of sediment, so I didn't flush the entire tank, only about 5 gallons. Would flushing it to empty make a difference?

I've so far been unable to get the anode unscrewed to check its condition, but that wouldn't effect temperature, right?

Anything else I should look into/try?

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    Do you experience the same thing at other faucets? Maybe your tub faucet's anti-scald mechanism is getting wonky. – isherwood Jan 27 '17 at 22:14
  • Nope, it's everywhere. Neither shower nor bath has an anti-scald setup - the bath has a limiter in the faucet handle itself, but that doesn't change. – Drew Jan 27 '17 at 22:45
  • What make and model is this heater? Also, is the burner cycling normally? – ThreePhaseEel Jan 27 '17 at 23:10
  • @ThreePhaseEel updated the question to answer your questions – Drew Jan 27 '17 at 23:35
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If this is an ordinary glass lined steel gas fired water heater it is likely at the end of its reliable service life. Get a new tank installed.

If you want to try a simple fix you could cycle the temperature setting knob by twisting the temperature set knob on the gas valve down to the lowest temperature, then up to the highest temperature and see if the burner comes on. Then turn the temperature knob down to the "recommended" setting--there will be a mark. Maybe you could set the temperature a little above this and it would work.

There is a temperature sensor probe which protrudes into the tank behind the gas valve and senses the temperature of the water inside. The burner turns on and off according to the state of this sensor. If this is malfunctioning, it could lead to the burner failing to come on sometimes or shutting off prematurely before the water has reached the set point. I think this is part of the gas valve assembly and not separately repairable or replaceable. The entire gas valve assembly is probably replaced as a unit.

This is not a job for the ordinary DIYer. You could call a plumber to do this repair, but almost certainly the water heater should be replaced.

The anode rod has nothing to do with this. Anode rods are well known to get stuck in place if they have been in service for this length of time.

  • I agree have had the thermostat fail in a few units. + – Ed Beal Aug 18 '17 at 13:19
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I would suggest that you shut off the incoming water to the tank, drain the tank and flush out the tank. You may also want to have a contractor remove the thermostat and clean all the calcium and other stuff that is coating the element. Lastly,as the temperature element controlling the temperature of the water get older they slowly loose their ability to correctly control the water temperature. It may be time for a new tank.

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