A.O. Smith water heater not heating?


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Old 01-17-17, 05:15 PM
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A.O. Smith water heater not heating?

Trying to save my parents a few bucks on a plumber if I can.

They've got a small electric hot water heater under their main bathroom to get instant hot water until their tankless can catch up. No re-circulation pump. They have noticed the first 4-5 minutes of the shower now has cool, room temperature water.

After about 5 minutes the water goes back to a nice hot temperature.

My theory is that the water in the small tank is not heating, and until that small tank has depleted, they are getting that pure cool water in the shower.

I checked the obvious stuff, breakers, wall outlet, temperature dial, etc. All looks good. I pulled the plug, made sure the little red temp warning/reset button hadn't popped out (it hadn't) and turned up the temperature dial a slight bit, plugged it back in and heard it hiss right to life. I guess (?) this is the noise it makes as it runs/heats? Ran for about 5 minutes and went silent.

I've attached a photo of the unit and the layout. The red tubing in the lower left of the picture is the main line coming over from the tankless on the other side of the home. The other main line that goes up and into the pex.

I will note that I notice the exhaust pipe had a leak sensor attached to the bottom of it, it wasn't blocking the pipe fully but it was slightly blocked. I'm not sure if partially blocking that pipe can cause any type of damage to these units (never worked on one) but there was no water leakage at all from the overflow pipe - Not a drop.

I've turned off the main line (eliminating the tankless) and am going to let the tank sit a couple hours then turn on the shower to see if the water that comes out has any heat to it at all - Any danger in running the tank empty? Should I only do this a few seconds? If I get lukewarm water, I can at least confirm the tank isn't heating, but then, what can I try next?

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I'd appreciate any advice, and thanks so much.
 
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Old 01-17-17, 05:23 PM
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I'm not completely following you but you cannot run any hot water heater empty.
After a half hour or so of heating the top red fitting should be warm.

If it only heats for 5 minutes you need to check for voltage on the element.

Exhaust pipe ? Do you mean discharge line on that small electric heater ?
I've never seen a sensor on the end of that pipe but it would have no effect on the tank heating.
 
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Old 01-17-17, 05:29 PM
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Sorry for my language barrier. I am a poor plumber. Thank you for replying!

It was a z-wave sensor he had connected as a leak detector below the white discharge pipe you see the top of in the photo. But it doesn't sound like that would have been the issue.

I let the tank fill up with water from the lower line and then shut it off so no more water could flow into the tank. This way, I figured when I tested the water above the tank, I would be getting pure tank water, not a 50/50 mix of tank water with any additional inflow from the tankless (realizing that little tank can only run for so long).

I will feel the top pipe in 30 minutes to see if it is warm to the touch. Simple way to test it, thanks. If it's not warm to the touch, what might be options be? I will note I have turned the temperature dial up a hair to around 130 degrees under the padding flap there. Is the element there or is it under that other plate in the center there? I have a voltage meter so can-do on that. I just never worked on a hot water heater before so I'm a little new at troubleshooting these. Totally new.
 
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Old 01-17-17, 06:14 PM
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Okay, perhaps I spoke too soon but I will check back in. The top fitting was very hot to the touch as was the top brass of the white discharge line there in the front. I ran the shower again (turned the main water line from the tankless back on though as I didn't want to risk running the 6 gallon heater dry during my test). This time, it stayed warm throughout the first 3 minutes without turning cold as it did the first time I checked it (that time, just as they said, lukewarm for about a minute, then, room temperature for around 3 minutes, then warmed back up).

What they may be experiencing here is the dreaded "cold sandwich" where the shower head is quickly depleting the 6 gallons of hot water in the tank, and then pulling in cold water from the tankless still before the tankless has had time to heat it up. I swear that in the past, the shower had not depleted the hot water from the small tank by the time the cold sandwich had mixed in enough to be hot, and you could never tell the difference. Maybe the colder temperatures here in the northeast mean that the water coming from the tankless lines will be colder for longer before it finally reaches temperature, and they just need to run the shower for 4 minutes the first shower of the day.

I'll test it again tomorrow for them before anyone has run any hot water to see what happens, and let the small heater run overnight and feel the brass fittings in the morning as well to check them for heat.

Thanks for sticking with me. I still sense something is not quite right here, I'm just not sure what it is before. For 2 years they have had this setup in their home and never once had the shower go warm for 1 minute, cold for 3 minutes, then hot. Something's going on here, I'm just not sure if I'm barking up the right tree...
 
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Old 01-18-17, 02:57 PM
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Turns out it looks like it is one of the 2 tankless Rinaii units that is cycling hot and cold. I will start a new thread if I can't figure it out. First thing I will try and do is isolate them one at a time to determine which of the 2 is malfunctioning.

Thanks and sorry for the misdirection.
 
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Old 01-18-17, 03:28 PM
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Not a problem. We're here to help.
 
 

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