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Old 02-09-2016, 11:38 PM   #15
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Are you sure the tank is stratified? You could try touching the cold water inlet at the bottom of the tank and see if it is hot.

Try disassembling the shut-off valve that is on the hot water out line. Someone once described how the internal washer/seat/seal had moved inside and was obstructing the hot water flow.

Also, I've never seen one, but I understand there is a new Atwood XT model that heats the water hotter than normal and has a built-in mixing valve. Could the prior owner have put one of these in, and that valve is not functioning properly?
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Old 02-10-2016, 01:39 PM   #16
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Are you sure the tank is stratified? You could try touching the cold water inlet at the bottom of the tank and see if it is hot.

Try disassembling the shut-off valve that is on the hot water out line. Someone once described how the internal washer/seat/seal had moved inside and was obstructing the hot water flow.

Also, I've never seen one, but I understand there is a new Atwood XT model that heats the water hotter than normal and has a built-in mixing valve. Could the prior owner have put one of these in, and that valve is not functioning properly?
I'll try the touch test. I can hardly reach the hot shutoff valve. It is on the side between the heater and the wall. If I decide to change the heater I can check it when I pull the heater. No real way to get at it otherwise.

This is the original Atwood heater from 2002, so no internal mixing valve.

I'm going to pull the overpressure valve and drain valves (again) and look inside. I'm also going to do the vinegar flush.

I also realized that perhaps the thermostat is bad (unlikely, but possible) and it is shutting off at a lower temperature and the water at the top is hot. I'm going to bypass it, leaving the emergency cutoff switch in place. I went ahead and ordered the shutoff kit from Amazon. Worth $11 to see if that fixes it before committing to a new heater.

Al
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Old 02-10-2016, 02:56 PM   #17
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OK, here's the status....
The AC and propane sides now both work in an equivalent manner. After an hour or so on electric or after the propane has run and shut off, the initial water from the faucets is very hot - probably a good 160 degrees, but it doesn't last. After 10 or 15 seconds it gets to just feeling warm and then will stay that way for several minutes, probably 6 gallons or so
Bypass valve.

If you're sure it's shut, then there's something wrong with it.
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Old 02-10-2016, 04:55 PM   #18
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Al, if your set-up is similar to mine, there is (barely) just enough space to get a small wrench on to the retaining nut under the valve handle. You could pull the stem out and look into the valve body with one of those small inspection mirrors that are on a telescoping handle.

If this is possible, I would look at the bypass valve as suggested by Jammer.
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Old 02-10-2016, 06:27 PM   #19
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Al, if your set-up is similar to mine, there is (barely) just enough space to get a small wrench on to the retaining nut under the valve handle. You could pull the stem out and look into the valve body with one of those small inspection mirrors that are on a telescoping handle.

If this is possible, I would look at the bypass valve as suggested by Jammer.
Thanks everyone for hanging with me here.

Well, the bypass valve is the common element between the two heating mechanisms, for sure. I'll try to get a look at it tomorrow. The bad news is if it need to be replaced I'm going to have to pull the heater to do it.

I filled the tank with vinegar and water 2:1 mix and fired off the heater. It only ran about 30 minutes. The specified recovery is 7.4 gal per hour so I would have thought it should have run close to an hour. I'll go out and check the temperature on the exposed inside wall with my IR thermometer.

Al
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Old 02-10-2016, 07:04 PM   #20
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I filled the tank with vinegar and water 2:1 mix and fired off the heater. It only ran about 30 minutes. The specified recovery is 7.4 gal per hour so I would have thought it should have run close to an hour. I'll go out and check the temperature on the exposed inside wall with my IR thermometer.
The recovery rate is based on a 90 degree rise. That is typical in northern states where the incoming water temperature is close to 50 degrees and the water heater is set for 140. With the higher incoming water temperature you have in Florida (usually close to 70 degrees), the rise is considerably lower. There is also some water that won't be heated right away due to a thermocline effect, about 10% of the capacity usually. So you are only heating 5.5 gallons. 5.5 * 70/90 / 7.4 * 60 minutes= 35 minutes.
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Old 02-10-2016, 07:07 PM   #21
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Well, the bypass valve is the common element between the two heating mechanisms, for sure. I'll try to get a look at it tomorrow. The bad news is if it need to be replaced I'm going to have to pull the heater to do it.
You might want to try turning it the other way (to what should be the "open" position), first, just to be sure it isn't set up backwards or something.
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Old 02-10-2016, 07:39 PM   #22
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You might want to try turning it the other way (to what should be the "open" position), first, just to be sure it isn't set up backwards or something.
That's an interesting point. The rig was supposed to have been winterized, but according to standard positions, the bypass valve was closed (perpendicular to the pipe) as were the inlet and outlet valves. I just assumed that they had not opened the bypass valve. But if the bypass valve was open, wouldn't I get warm water from the cold side of the faucet? When I turn the faucets to cold, I get pure cold water, not warm.

Maybe they didn't use the bypass valve because they winterized it with RV antifreeze.

I just measured the temperature of the inside wall of the tank with my IR thermometer with curious results. The top was around 97 degrees, the bottom was around 100, and the center was below 80. That seems odd. It may just be due to the reflectivity of the tank wall since I was shooting horizontally and the top and bottom were curving away while the middle was perpendicular to the measurement line.

In about an hour I'll go drain the vinegar solution and see if any deposits come out.

Al
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Old 02-10-2016, 07:43 PM   #23
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The recovery rate is based on a 90 degree rise. That is typical in northern states where the incoming water temperature is close to 50 degrees and the water heater is set for 140. With the higher incoming water temperature you have in Florida (usually close to 70 degrees), the rise is considerably lower. There is also some water that won't be heated right away due to a thermocline effect, about 10% of the capacity usually. So you are only heating 5.5 gallons. 5.5 * 70/90 / 7.4 * 60 minutes= 35 minutes.
Thanks for the definitions for the standard - I put in 3.5 gallons of Vinegar that had been sitting out in about 45-50 degrees and about a gallon of water at the same temperature because it was in a hose roole up on a reel.

Al
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Old 02-10-2016, 09:31 PM   #24
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I went out to drain the vinegar solution and the heater was running. I waited until it shut off and made another temperature measurement. It was about the same as the first. Nothing came close to 140 degrees. The highest temperature I measured was 115 up on the top of the tank, presumably in the air bubble.

After it shut off I drained the tank. After soaking in the hot vinegar solution for 2 hours, the water came out crystal clear. I don't think I have a sediment or calcification problem.

Tomorrow, if I can figure out an easy way to do it, I'm going to jumper the thermostat and let the emergency cutoff shut the heater down. I think it is the same temperature as the thermostat, just serves as a redundant means of turning off the heat. My new thermostat and ECO kit will come on Friday.

I was confused about the bypass valve. It is in front of the heater on the inside. It should be easier, if not easy, to take out and inspect. That's the next step after bypassing the thermostat.

Al
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Old 02-11-2016, 08:45 AM   #25
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I would also suggest measuring the actual water temperature. The thermostat should get it to 140 and the ECO a lot hotter.... not sure exactly, but it would be scalding.
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Old 02-12-2016, 01:25 PM   #26
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OK. I shorted out the thermostat (labelled at 140 degrees). The heater ran substantially longer and the temperature at the top of the tank got up to around 125 degrees before I turned it off. The ECO is labelled at 180 degrees, and did not open. There was still an odd vertical temperature gradient in the tank, cooler in the middle and warmer at the bottom and the top. This gradient occurred prior to opening any faucets so should not have been caused by cooler water flowing in. I turned on the water at the lavatory and observed the same phenomenon as before, i.e. the water was at first very hot, then cooled then warmed. But the hot water lasted longer and I ultimately got hot water at the galley sink which I had not seen before. I also ran some water into a plastic cup and measured the temperature with a candy thermometer. The measurements were consistent with the IR measurements on the outside of the tank. I also operated the bypass valve. My conclusion is that it is correctly set and operational.

I am considering the possibility that the cold water entry pipe inside the tank has broken off. The pipe directs the cold water to the bottom of the tank. If it has failed, then the cold water enters at the middle. I'm not sure how I would confirm that without a bore scope, but if the new thermostats don't correct the problem that's probably my last test before just giving up and buying a new heater.

Al
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Old 02-12-2016, 05:32 PM   #27
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I do not know if the gradient you describe is abnormal, particularly if it is small. Look at how the flue runs in this photo:

http://beamalarm.com/Documents/water..._cut_open.html

Depending on where you measure the temp, I could see it warming more at the bottom and top of the tank, where you are closer to the flue, if it has not had time to thermally mix.

The idea of the broken cold water entry pipe also sounds a stretch. Check out this pic:

http://rvtravel.com/blog/rvnow/2008/...ential-rv.html

It would have to break right at the bend in the pipe. Possible, I guess.

I would still try to open up the bypass valve to see if it is closing properly.
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Old 02-12-2016, 06:25 PM   #28
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Quote:
Originally Posted by Siegmann View Post
I do not know if the gradient you describe is abnormal, particularly if it is small. Look at how the flue runs in this photo:

http://beamalarm.com/Documents/water..._cut_open.html

Depending on where you measure the temp, I could see it warming more at the bottom and top of the tank, where you are closer to the flue, if it has not had time to thermally mix.

The idea of the broken cold water entry pipe also sounds a stretch. Check out this pic:

http://rvtravel.com/blog/rvnow/2008/...ential-rv.html

It would have to break right at the bend in the pipe. Possible, I guess.

I would still try to open up the bypass valve to see if it is closing properly.
I'm going to feel really stupid if it is the bypass valve. I'll try that tomorrow.

I have read of this exact set of symptoms caused by a broken cold water feed pipe in a home water heater, that's why I considered it a possibility. I may pull the electric element and look in there; it's a bigger hole.

Al
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