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Old 08-05-2010, 08:56 PM   #1
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Gas Water Heater, water not hot enough - Thermostat or Sediment


I have Bradford White 75lt Gas Water Heater model# MI75S6BN in my brand new home that I bought less than 2 years ago. I always keep my thermostat one notch below the mark (I think that is 120F mark) and I never had any problem winter or summer. Suddenly water is not hot enough as it used to be, its just luke warm. I checked thermostat setting and its at the same place.

I turned the thermostat up and I heard burner lit. I immediately turned it back to same setting as before. We had hot water for 2 days and again water wasn't hot.

I didn't know anything about water heater but after 6 hrs to google search and reading, got a fair idea on how it works. I checked pilot and it was on, but the burner was off even though there was no hot water. I again turned the thermostat up and I saw burner lit. This time I didn't turn it back to where it was. I have hot water now, but its just a few hours. I will know in few days if water goes cold again...

Just fyi, weather is hot around 90 degrees for weeks, so I don't think it has anything to do with the incoming water being too cold..

Do I have a problem in my water heater? Can it be sediment (we have never drained our water heater since we bought this house, little less than 2 years - will do this weekend) or more like thermostat/gas valve?

My builder warranty says 2 years on plumbing but builder is refusing saying that water heater is not covered under plumbing. Manuf. won't pay for labor or diagnosis...Please help.

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Old 08-05-2010, 10:23 PM   #2
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Gas Water Heater, water not hot enough - Thermostat or Sediment


You may have a failed single handle cartridge in one of your faucets or tub allowing cold water to bleed into the system. Check for drips at all your faucets.

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Old 08-06-2010, 11:31 AM   #3
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Gas Water Heater, water not hot enough - Thermostat or Sediment


Thanks for your response. I checked all my faucets and don't see any drips. Is there a way to make sure that thermostat is working properly?
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Old 08-06-2010, 08:55 PM   #4
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Gas Water Heater, water not hot enough - Thermostat or Sediment


Drain any sediment out of the tank for good measure. This should not require draining more than five gallons.

Have handy a screw on garden hose cap such as from a daisy chainable lawn sprinkler. Just in case the water heater drain valve doesn't close again completely.

Turn off the washing machine faucets and also be sure that showers, etc. are turned off using the wall faucets and not the sprayer vs. shower head control. Commingling of hot and cold water sometimes happens this way and there might be no visible dripping.

If you wait half an hour between showers, dishwashings, etc. is it only the first person's shower that is cold?

If you turn the water heater thermostat up just a little and then turn it back to where it was, does the burner keep running for awhile and then the hot water problem is cured for that day?
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Last edited by AllanJ; 08-06-2010 at 09:07 PM.
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Old 08-07-2010, 08:30 AM   #5
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Gas Water Heater, water not hot enough - Thermostat or Sediment


The dip tube probably disintigrated. The dip tub sends cold water to the bottom of the tank for heating when its heated it rises to the top of the tank. Its possible that the dip tube broke of and now you have cold water mixing with the hot water on top.
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Old 08-07-2010, 11:17 AM   #6
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Gas Water Heater, water not hot enough - Thermostat or Sediment


Thanks for your response guys. I never owned a house before, so trying to learn few things and so please bear with me.

Regarding:
"If you turn the water heater thermostat up just a little and then turn it back to where it was, does the burner keep running for awhile and then the hot water problem is cured for that day? "

==> That's exactly what I noticed. What does this mean?

Another thing I found on internet and tested:
"I confirmed that burner was not on; I opened all hot water faucets for some time and noticed that after some time burner turned on"

I also drained water heater yesterday. Here is the one thing I noticed.

"While draining I opened all hot water faucet to take air out. What I noticed that the shower faucet in the basement was dripping constantly even though it was completely on the hot position. None of the other faucet was dripping. We never ever use basement shower. Is this the dripping you guys are talking about which might be mixing hot and cold water?"

jc60618, is there an easy way to check dip tube?

Thanks everyone !
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Old 08-07-2010, 05:32 PM   #7
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Gas Water Heater, water not hot enough - Thermostat or Sediment


Quote:
"While draining I opened all hot water faucet to take air out. What I noticed that the shower faucet in the basement was dripping constantly even though it was completely on the hot position. None of the other faucet was dripping. We never ever use basement shower. Is this the dripping you guys are talking about which might be mixing hot and cold water?"
Was it dripping when you had it open or does it always drip?

If it was dripping after you shut the water off, that's because that's the lowest fixture in the house and will take longer to drain than all the others.

If it always drips, then you should change the cartridge. That's most likely the culprit considering everything is fairly new.
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Old 08-07-2010, 09:11 PM   #8
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Originally Posted by LateralConcepts View Post
Was it dripping when you had it open or does it always drip?

If it was dripping after you shut the water off, that's because that's the lowest fixture in the house and will take longer to drain than all the others.

If it always drips, then you should change the cartridge. That's most likely the culprit considering everything is fairly new.
It was dripping only when I had it open. It doesn't drip always.
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Old 08-07-2010, 09:16 PM   #9
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Gas Water Heater, water not hot enough - Thermostat or Sediment


Quote:
Originally Posted by makunag View Post
Another thing I found on internet and tested:
"I confirmed that burner was not on; I opened all hot water faucets for some time and noticed that after some time burner turned on"
UPDATE: The above test was done when I had changed my thermostat setting to high. Yesterday after draining my water heater I put back the thermostat to my original setting (warm); my burner was on and I had hot water for 24 hrs. Exactly after 24 hrs my water running cold again. Saw burner was not on; I opened hot water faucets for long time; the burner DID NOT turn on. I changed thermostat to higher setting and it turned on.
Are we close to rule out few things?

Thanks as always.
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Old 08-07-2010, 09:56 PM   #10
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Gas Water Heater, water not hot enough - Thermostat or Sediment


Could be a problem with the gas valve (thermostat). Call the number on the water heater and they'll run through some diagnostics with you over the phone. It's still under warranty, so once they determine the problem they'll most likely send you the appropriate parts.
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Old 08-08-2010, 12:32 AM   #11
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Gas Water Heater, water not hot enough - Thermostat or Sediment


If you turn up the water temperature and immediately put it back and that cures the problem of water not hot enough, then the threshold for turning the heater on is too low compared with for turning the heater back off. If using lots of hot water still doesn't turn the heater on then the two thresholds are way too far apart. This can be due to sediment caked up on the immersion part of the thermostat, or can be due to a defect in the thermostat mechanism.

You might find it works better by always using a hotter thermostat setting. This is okay provided that the water is not way too hot some of the time.
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Old 08-08-2010, 10:40 AM   #12
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Quote:
Originally Posted by AllanJ View Post
If you turn up the water temperature and immediately put it back and that cures the problem of water not hot enough, then the threshold for turning the heater on is too low compared with for turning the heater back off.
Yes seems like that is the situation, because it works for around 24 hrs and then the burner doesn't turn back on..

Quote:
Originally Posted by AllanJ View Post
This can be due to sediment caked up on the immersion part of the thermostat.
We drained the heater but hardly found any sediment coming out. Any better way to clean?

Quote:
Originally Posted by AllanJ View Post
You might find it works better by always using a hotter thermostat setting. This is okay provided that the water is not way too hot some of the time.
A higher setting is seems to be working for now....I'll have to watch for few days though. Is there no issue just leaving the thermostat at higher setting? Its not too hot by the way.

Thanks a lot.
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Old 08-08-2010, 11:36 AM   #13
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Gas Water Heater, water not hot enough - Thermostat or Sediment


Getting a little technical.

If both the turn on threshold (low temp) and turn off threshold (hi temp) have shifted by roughly the same amount, then leaving the thermostat up higher is a near perfect solution.

If just the turn on threshold has shifted and by a large amount, then you cannot leave the thermostat higher because then the water will get too hot.

You would have to disassemble parts, namely disconnect the gas and remove the control panel from the water heater to inspect and clean the thermostatic immersion element. For an older heater it is not worth the trouble.

Too hard to say whether the immersion element or the linkage to the gas supply valve (or switch) is causing the thresholds to change.
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Last edited by AllanJ; 08-08-2010 at 11:39 AM.
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Old 08-09-2010, 07:33 AM   #14
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Gas Water Heater, water not hot enough - Thermostat or Sediment


Just throwing this out maybe to help find the gremlin causing the problem.

Is it possible the immersion element has built up a coating of sediment / minerals and is sort of throwing off the thermostat a few degrees??

I think Alan is on to something I would pull the sensor and clean it.
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Old 08-27-2010, 09:45 PM   #15
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Gas Water Heater, water not hot enough - Thermostat or Sediment


I had a similar problem in the apartment I just moved into. I have a 40 gal AO Smith gas hot water heater that is about 6 years old. Some days I have decent hot water, other days it is barely lukewarm. While testing it, I ran the tub faucet open full and ran the hot water temp down from 105F to 85F, and the main burner had not lit yet. (The thermostat was set at "B" which is supposed to be 130F.) If I twisted the thermostat manually just a nudge, the burner would come on. Sometimes when heating the tank would make popping and other noises.

I assumed there was some defect in the thermostat. I called the manager and someone came by and "drained" the tank. (I assume they flushed some or all of the water, I'm not sure since I was not home.) Since then, it seems to work much better. I almost always have decent hot water for showing and washing dishes, and I have not bothered to get my thermometer out to check the drop and relight temps.

My suggestion to the original poster here is to drain your tank. I've been reading that the thermostat or burner can become coated with sediment.
Set the thermostat to the pilot setting, shut off the incoming cold water and drain most of the tank. Then turn the cold water on for a minute to stir the remaining sediment.

My question to the experts is, is this a reasonable scenario? Should my HWH work well now, or should I expect that it will return to the previous behavior sooner or later? If the thermostat is bad, what kind of evidence or test can I do to convince the manager to repair or replace it?

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