Hot water heater reset button tripping on old and new HWH

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BigEdgar

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Hi, we have a 40 gallon electric hot water heater in a small apartment above a garage on our property. When we bought the house, the HWH would occasionally stop heating water and I'd have to hit the red reset button on the tank, at which point the water would heat again for a while, only to trip the reset button again sometime later. There were some spare parts near the HWH that lead me to believe that the prior owner had the same issue and tried to remedy the problem through some homeowner repairs (these obviously didn't fix the problem).

A few months ago, I bought a new Rheem 40 gallon electric unit and installed it myself, happy to be rid of the problem. Well, after a few weeks, I noticed that the water wasn't hot any longer, and sure enough, the reset button on the brand new unit had been tripped. I've researched the usual root causes for the reset button being tripped, and since this same issue occurred on the old unit as well as a brand new unit, I'm inclined to believe that the issue is outside the HWH. My question for the brains on this forum – what else could it be, and how do I troubleshoot? The two most logical theories I can come up with are:

  1. The wires from the panel to the HWH are compromised somehow – perhaps the wires got nicked somewhere along the way. If this is the case, is there any way to test the wiring to prove this theory out? Or is my only option to replace the wiring (this will require opening up a lot of finished walls, so it'll suck).
  2. The HWH is tucked into a closet and is in a pretty tight space. Perhaps the ambient temperature causes the high limit switch to trip? Is there any way to test this theory (crank the heat way up in the apartment and see what happens?)?
Do those theories make sense? Anything else I should consider?

Thanks!

wh-reset-button.jpg
 
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Jadnashua

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Check the inlet voltage to the WH.

Verify that the inlet voltage matches the acceptable range on the WH involved.

There should be three wires: L1, L2, and ground. The voltage between L1 and L2 is the one you're interested in. The power should be coming from a double-pole breaker (which is why it is 240vac - L1 and L2 are connected to the two contacts on the breaker). I suppose there might be a WH that needs neutral, but those I'm familiar with do not, at least 240vac ones.

A few places might have 208vac verses 240...and, the WH must match the supply voltage. Using a 208vac unit on 240 might cause it to draw more power than it was designed for.
 

BigEdgar

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Thanks very much, Jadnashua. I'll measure the voltage next time I can get access to the unit. FWIW, the wire for this unit has 2 hots, a neutral and a ground coming from the panel. I just capped the neutral at the HWH as it's not needed. And you're right, it does come from a double pole breaker (I think it's 2x30 amp breakers, which should be enough for the HWH)

Does the second theory of "maybe the ambient temps are overheating the high limit switch b/c the HWH is in a tight space" seem likely? It gets warm in this corner, but never near the 180 degrees that I believe are required to trip the high limit switch.
 

hj

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NO. normally, the cause would be a bad element or a loose wire on the thermostat, but either of these would be cured with the new water heater. Frequent uses of small amounts of hot water COULD cause it, but you do not indicate that that is how you use hot water from this heater.
 

BigEdgar

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Thanks, HJ - it's an interesting thought. We don't use this apartment that frequently, and when we use the hot water, it may be for someone to just wash their hands or clean something off real quick, and then it could sit unused for days or weeks at a time. I suppose draining a small enough amount to cause the element to kick on could raise the temp of the hot water to past 180 and trip the high limit switch.
 

Master Plumber Mark

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Check the inlet voltage to the WH.

Verify that the inlet voltage matches the acceptable range on the WH involved.

There should be three wires: L1, L2, and ground. The voltage between L1 and L2 is the one you're interested in. The power should be coming from a double-pole breaker (which is why it is 240vac - L1 and L2 are connected to the two contacts on the breaker). I suppose there might be a WH that needs neutral, but those I'm familiar with do not, at least 240vac ones.

A few places might have 208vac verses 240...and, the WH must match the supply voltage. Using a 208vac unit on 240 might cause it to draw more power than it was designed for.

that is probably the cause of your issues.....
you probably have too much juice coming into the heater.....
at least that is a good theory....
 

Phog

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I'm not sure what to make of the low voltage theory.

Excess heat causes the limit switch to trip out. Heating is proportional to current flow. Current flow is proportional to voltage (across fixed resistance). Therefore at lower voltage there will be less current flow, less heating, and smaller chance of tripping the limit switch -- no?

The water heater elements would have to stay on longer to reach the water temperature setpoint, yes, but the amount of current flow & the heater element temperature during that "on" time would be proportionally less... Maybe there is a variable I'm not seeing though.

One thing that I would check for would be contact resistance at the incoming wire connections. If the wires ends are in poor shape, for example if they are coated with old electrical tape residue or corrosion, there would be heat generated by poor metal-to-metal contact at the connection point. This heat wouldn't have to conduct very far to trip the limit switch, which is usually right next to / integrated with the incoming electrical terminals.

This isn't by any chance one of those old circuits with aluminum wiring, is it?
 

Jadnashua

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If your elements are designed for 208 and you feed it 240, the element will try to get hotter because it will use more current. This is why I asked you to check the inlet voltage and the label on the WH to make sure that what you have corresponds.
 

Phog

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If your elements are designed for 208 and you feed it 240, the element will try to get hotter because it will use more current. This is why I asked you to check the inlet voltage and the label on the WH to make sure that what you have corresponds.

Ahh yes -- I read your original suggestion backwards (240V heater on 208V supply).
 

BigEdgar

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All - I know it's been a few months since I posted this topic, but I just now got a chance to get back at this project. Per Jadnashua's suggestion, I measured the voltage at the HWH. It's showing 244 volts during it's heating cycle. Is that normal? Seems high. Also, I confirmed that the HWH is rated for 240 volts per the label on the front of the unit.

Here's a photo of where I measured the voltage and how it reads on my multimeter.

https://imgur.com/a/c1PxdEl
 

Reach4

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It's showing 244 volts during it's heating cycle. Is that normal? Seems high.

Not high. Nominal is 240, and 10% over that is 264. 5% over is fairly common in many places.

Use the clamp ammeter, maybe on that red wire in your photo, or at the breaker box, after the WH has been off so the water will have cooled. One wire only.
 
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JerryR

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It sounds like the problem is in the water heater, not the supply voltage.

Like HJ said your water heater is dual voltage. Look at the label it probobly states 4500/3380 240/208v.

The usual causes of tripping the overtemp is either a shorted element or a sticking upper or lower thermostat.

Here’s a simple YouTube video
He’s my kind of guy. :)
 

WorthFlorida

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On this new water heater have you ever adjusted the temperature settings? The thermostats on water heaters are quite common and just about everyone uses the same thermostat. They are fairy inexpensive ($15-$20) and very easy to change out to give it a try. As suggested a clamp meter can be used to measure the current while a heating element is on. Each one will take about 18 amps and only one will be on at a time.

https://mspplumbingheatingair.com/blog/why-does-my-electric-water-heater-reset-button-keep-tripping
 

BigEdgar

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Wow, thanks for the continued support on this issue, everyone - you guys are truly awesome!

FWIW, I confirmed what HJ and JerryR noted, that the unit *is* dual voltage according to the label on the side of the unit.

So the plot thickens... I followed the video that JerryR posted (BTW, that guy in the video is awesome - he helped me troubleshoot a busted solenoid on my riding mower this summer!). What I discovered is that the lower element appears to be blown. Upper element measures 12 ohms of resistance when measuring across both leads on the element (which apparently means the element is good), the lower measures zero ohms of resistance (which apparently means it's bad). In addition, there's a burn mark on the plastic covering for the lower element. Here are some pictures of the measurements: https://imgur.com/a/9BYkizE

To top it all off, after this round of troubleshooting, I can't get the HWH breaker to turn back on back at the panel- it keeps popping. Perhaps in my troubleshooting I knocked the element loose and now it's in contact with the body of the HWH causing a short. Additionally, I noticed that one of the aerators for a sink that is fed from the HWH got clogged up - another possible clue that something inside the HWH is loose/broken.

I ran out of time to troubleshoot further this weekend, but I believe next steps are:

  1. Drain the HWH and replace the lower element.
  2. After that, measure the current for each of the wires feeding the HWH at the electric panel to confirm that I'm getting the expected amps flowing when heating - I still have some suspicions that the wiring may be off somewhere, and this may help me confirm that the wiring is sound.
Hopefully a new element fixes this problem. As noted above, I do have some nagging feeling that there's something else going on. Why? Because this brand new HWH had the same symptoms as the one I just replaced (thermal limit switch tripping). It's possible that the lower element on this new unit got damaged in transit and it's just a coincidence that this unit shows the same symptoms as the old one, but I'm also a little suspicious that there could be something else going on with the wiring (or perhaps the breaker?). Anyways, I'll replace the element and find out.

Thanks again for the terrific help, everyone!
 

Jadnashua

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Just a pet peeve...if the tank was already hot, why would you heat it? It's a water heater.

FWIW, if you're fast and you shut off the inlet supply, you can usually change the element without losing much water from the tank. Personally, I've not tried it, but think finger over the end of a straw.

I'd probably still drain it, but I'd shut it off (assuming it's hot, probably isn't any more!), take a nice hot shower until it turned cool, then drain the now cool water versus a tank of hot.
 

BigEdgar

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Ha, that's funny - I was wondering why people on these forums call it a water heater. I figured it was a lazy way to say hot water heater. But you're right - it's just a "water heater". The unit will be cold when I'm there next, so it'll be easy to drain. Thanks!
 

Phog

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If you're measuring a short (zero Ohms across the heater element), then I would expect the breaker to trip just as you are seeing. As soon as the thermostat kicks on that element, there will be "infinite" current flow and the breaker will pop.

EDIT -- I just noticed that you said it's the bottom element that is shorted, but the breaker trips immediately. The bottom thermostat shouldn't be able kick on until the top thermostat turns off, which wouldn't be for quite some time after power-up.

So, for the breaker to blow immediately without the lower element powered on, you would need a short to ground. What do you measure between the lower element and the tank shell? Does it also read zero Ohms?

Either way, the element is almost surely what is causing the breaker to trip.
 
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Phog

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Thanks, Phog - I measured zero ohms between the bottom element and the tank body (see third image down here: https://imgur.com/a/9BYkizE.

Ahh yes, I see now, very helpful pictures. In the bottom picture (where you are measuring the resistance of the lower element), the meter is actually not reading zero ohms, it's showing "OL", which means "open loop". This means the meter is seeing very high resistance, in fact so high the meter can't measure accurately.

This doesn't change anything, you still have a ground short which is causing the breaker to pop, and replacing the heater element is still necessary. You definitely did have a "thermal event", as you put it ;)
 
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