Water heater issue again!

[edy]

I have a small simple space-saver water heater with a 120V 1500W element. It was working fine for 7-8 years, then stopped working. I changed the element and thermostat control box (the one that clips to the side of the tank) just in case and it worked for another 3-4 months, then died again.

So I called plumber, the figured maybe the tank has an issue and sediments, anode couldn't be pulled out, so we decided just to change to a new tank of same rating/size. Left it over the weekend (this is an office install) and come back Monday morning no hot water.

Power to element 120 V going in. Element ohm rating in the 4-5K ohm and going up. Normally should be around 10 ohm for a 120V 1500W which should draw 12.5A. Same thing that happened to my other 2 elements before that failed. This was brand new tank though, new element, new thermostat.

We are now scratching our heads, as well as plumber, wondering what is going on. He wanted to call an electrician to see if maybe something with the panel but I don't know.

Here's what I do know:

1. The wires from the thermostat (going to element) show 120 V AC
2. When I switch panel breaker off, I am still getting about 1.25 V AC (not 0)
3. The element is showing too high ohm reading, although it is in water (still installed in tank) I would still expect low readings, not that high.
4. I don't think it is electrical issue but then why are my breakers showing 1.25V AC even when off

We suspected maybe hot/cold is mixing somewhere and the tank is running all the time. If it was electrical issue, it would have probably not worked from the beginning. But because it was installed Friday afternoon everyone left, thinking the tank was warming but it could have just been getting to ambient room temperature. So could be it never worked and element faulty from the beginning, or it burned out before the tank filled.

Anyways, at this point... plumber going to change element first. He'll look at tank contents and see if there is any crud or contaminant that could have caused an issue. We are also going around office and checking and disconnecting all things that have both hot/cold where a mixing valve could have an issue and allowing cold to get back in the hot tank, which would then cause cold water to backflow into the tank and cause element to run constantly and thus burn out.

Finally, we check for any leaks to make sure tank is not draining somehow (we have some backflow preventer and other valves which in case of pressure changes they drain directly into some traps so keep water in them)... those would drain slowly without us noticing any puddles on the floors. The water is shut off during the night, we shut back on day. So it could theoretically drain the plumbing in the office including tank.... But I never notice "filling" in the morning, we have water right away so that can't be it.

I know this is an electrical forum not a plumbing one, but I would appreciate knowing if you think it could be electrical before my plumber starts to bring in the electrician and entire army. :-) Thanks!



 

[Samogon]

kOhms on heater most likely indicate it is dead, where did you bought it? Can you just return it as bad item, what return policy is?
few volts floating around on AC can be seen if you not using Zlow on DMM.

[Seekonk]

You might be running out of water and that causes the elements to open when they overheat.  Some water systems require you to have check valves to prevent water from draining out of the system when there is work on the mains.  Not rocket science, the elements should be in the low ohms. I do a lot of PV water heating and buy the 2000W 120V elements which are 7.5 ohms.  The last ones I bought came from Cambodia.  It could be just a quality issue. If they overheat they go bad, they are supposed to.

[TheUnnamedNewbie]

Few volts AC with a multimeter is just because you are pretty much building parasitic transformers.
Is it possible that a device somewhere else in your plumbing system has suffered a fault and is now causing some sort of electrolytic reaction (maybe some kind of other metal that is connected through the ground forming a electroplating system, destroying your heater and depositing the metal somewhere else)?

[tablatronix]

air in tank,  blown element is my guess. Check for leaks

[edy]

Hi, Thanks for the replies.

I confirmed the element was bad, we changed it and it heated up the tank again. I set it to "medium" heat but the water from the tank feels scorching hot, and the element continues to stay on even though it seems to be over the temperature setting I set it at. 

So that sounds like a bad thermostat that keeps the element going forever until it fries... But then it should have boiled the tank right? And we would have had the pressure release valve open if it kept the element hot all the time.

When I turn the little temperature set screw on the tank to below the set-point I can hear it click and can even confirm the element turns off (I get 0V on it with my meter). When I turn it back up to the temperature set, it clicks on again. So that seems to be working.

However, random times of the day when I go to the tank, I check it, the element is on. Always seems to be on.    The plumber said maybe some cold water is mixing in through a bad valve where hot/cold equipment or tap is used, and pushing cold water through the system back into the tank in reverse. That would chill the water along the hot line. But I have found the contrary... the hot line is scorching, element is on, yet the thermostat (brand new) seems to click properly and turn element on/off as I turn the set screw.

[HackedFridgeMagnet]

check the current changes as it switches. Current clamp meter or look at the houses main meter when everything else is off. It may have a red led flash every Watt-Second which would be often if the water heater was drawing current. then when the HW switches off the led should stop flashing.

it does sound like the thermostat is mis-wired, if it is anything like our ones it will be in series with the active.

another common problem with HW are the tempering valves. Not sure it applies to your description but they do go fairly regularly.

[edy]

Thanks for the suggestions. I am thinking of logging the element to see when it is cycling on/off during the day and plotting it. This way I can see if certain equipment in the office are on on certain days, it may be either mixing hot/cold or using more hot water than expected and causing the element to run constantly.

What is the best method to do this?

My first thoughts is to use my Arduino perhaps hooked up to a laptop via USB that is getting serial reads back from one of the Arduino's GPIO's.... unless I can figure out how to make the Arduino work "Stand-alone" by saving the data locally to memory and then reading off the data later.

As far as hooking up to the element, I need to detect whether a current is passing through the 120V A/C line. There are a few ways to do this:

1. Inductive:

I can get a thin wire or some coil and wrap it around one of the A/C leads to the element. If there is current in the 120 V AC wire it should induce current in my loop. I connect my loop to a rectifying circuit to get A/C and add a capacitor to smoothen it out and I would expect to see at least some constant DC voltage when AC is on...  As long as I get something other than zero I can log it, I know the element is on. If the A/C is off, the coil does nothing, I get zero voltage. Like this:

https://electronics.stackexchange.com/questions/280705/simple-wire-loop-for-detecting-ac-mains-activity



2. Signal lamp LED/photo-diode:

I tap in a standby/light indicator in series on the element and use a photodiode on my Arduino to sense for light. Sort of like this:

https://www.amazon.com/Plastic-Indicator-Signal-Green-Light/dp/B00HR4V0LK

... and then this...

https://outsidescience.wordpress.com/2012/11/03/diy-science-measuring-light-with-a-photodiode-ii/

Then I would just stick the signal lamp and arduino/diode in a light-proof box, tape them together and they are opto-coupled. I can see when my indicator light when it is on and off.



What do you think? If I can get an idea of what my element is doing during the different days my office is operational I can see why it has had a tendency to burn up or stay on too long.
 

[HackedFridgeMagnet]

You could use a power logger but wouldn't bother. (Logging meter with a current transformer and a burden resistor? )

Make sure the power is going on and off with temperature. Water should be very hot anyway > ~65C but not 100C unless its solar. You can probably check this with a K thermocouple and a multimeter.
Run the hot tap  to cool it down, but wait till it heats up.

If it is going on and off it is working.
Also check the voltage is 120v and not something else which would burn out the element.

[edy]

Yes, thanks for the suggestions. I did check voltage on the element and it is 115V and does cycle on and off periodically. I can hear the "click" and also the voltage goes to 0V when off. I used a thermocouple with my multimeter and I have the tank set to the lower end of the scale and temperature is about 50 C, which is still scolding hot for me, but we are not drinking the water.

I think the problem is fixed but for a while the plumber was running circles wondering why the brand new tank/element he installed burned out in 3 days over a weekend. So we went to all lengths trying to figure out if it was an electrical problem, cold water leakage across a tap or regulator, drainage of the tank, etc.... And couldn't find any obvious culprit. So he changed to another element and so far it is working.

I was also concerned because the first element lasted 8 years, and the new one I put in my old tank lasted 3-4 months. Then the new tank/element installed professionally by a plumber lasted 3 days while the office wasn't even in use... So we got suspicious. Maybe it was all a fluke?

Nevertheless, installing a logger would give me a graph and some idea of whether there is any change in the behaviour of our tank on certain days when certain processes in the office are happening that may affect the cold/hot water usage. I could then know if it was something to do with our systems and something being broken/leaky, or whether it was indeed all a big coincidence.

[HackedFridgeMagnet]

Might be this type of effect.

https://en.wikipedia.org/wiki/Bathtub_curve

[Gregg]

Veris Industries makes a group of split CTs that have internal switches that can be set to change state at an adjustable amperage.  Ebay should score you a used one at a reasonable price, but first look up what exact model you need http://www.veris.com/Category/Current-spcMonitoring.aspx
This should make it fairly easy to log time on / off

[kleblanc]

Hot water heaters typically last 7 years depending on their size and usage.  Smaller the size and the more usage, the quicker they can go. They will build up scale in either gas or electric heaters. On the electric ones they will eat away at the cathode or anode in the tank, I can't remember which one it is. Some tanks have replaceable cathode/anodes to extend the element's life.

When you go to monitor it and if it's possible I would try to isolate the water outlet of the tank at the shut off valve which you hopefully have since you just replaced it. This way it would rule out bad mixing valves or leaks elsewhere.  There would be not hot water available though so I would do it at night or while you are gone during the day.

There should be a thermocouple or a rtd for the controller that you might be able to tap into and record what the controller is seeing as well.