Electric water heater questions.

[K_W]

Our water heater tripped its own breaker, not the electrical panel breaker.

I suspect it has a bad element but both have reasonable resistance when tested.

the heater takes 3800w upper / 3800w lower - or - 3800w upper / 5500w lower for it's elements but it has a 3000w upper and a 5000w lower right now. the upper read 15.8 ohm and the lower read 9.3 ohm.

I don't have specs on what they should read but the reading seemed reasonable for the respective wattages.

I replaced one or both of the elements in the last handful of years, and I suspect one went bad. but last time no breaker tripped.

I reset the breaker button on the heater and turned the power back on and I could hear it start working again.

My question is... Could it be the control unit, meaning a whole new unit?

 

[skulhedface]

Your lower seems a little low to me. I would expect it over 10. Might just be a nuisance trip though. Wouldn't worry about it if it doesn't trip again.

 

[GodFearinGunTotin]

Those resistance readings are pretty close for those wattages @ 220v. I found this that has some good troubleshooting tips in it:

How-to-troubleshoot-electric-problems-with-water-heater

 

[K_W]

I read some of the link... the water did seem unusually hot last night when I washed my hands. I almost burned myself where I normally have fairly warm water at the same faucet positions.

I'd bet one of the element is shorted and not shutting off.

 

[CountryBoy19]

Might just be a nuisance trip though. Wouldn't worry about it if it doesn't trip again.

This^^^ I would just keep an eye on it. I had the same thing where I went through a 2 week period where the element would trip every couple days. I was about to order a replacement element and it never did it again... been going 3 years now.

 

[GodFearinGunTotin]

I read some of the link... the water did seem unusually hot last night when I washed my hands. I almost burned myself where I normally have fairly warm water at the same faucet positions.

I'd bet one of the element is shorted and not shutting off.

Just make sure your overpressure valve is working until you get this fixed. Have you ever seen pictures of where a water heater has come out of the basement and up through the roof of a house when they overheated?

 

[K_W]

I have seen the result. I test the valve from time to time and it does release wateI, I will test again today. I am going to buy two new elements and see if I can get a look at the anode and drain the sediment.

I am thinking of just replaceing this heater soon as the compliance sticker says 1994 and i can find no other dates on it.

 

[Mr Evilwrench]

W=V²/R. At 240VRMS, a 9.3Ω resistance would yield 6193W, so you're in the neighborhood. Your AC voltages are measured in RMS (root mean squared) as that is equivalent to DC. 120VAC actually peaks at about 170V. Resistance can change a bit when current is applied, though, mostly due to heat.

 

[K_W]

6193w is too high. i will test again as I was going by memory when i wrote the post.

 

[K_W]

I just checked on it on my lunch break, after no one being home for 5 hours, the elements were still on and I was getting a hundred and eighty degree water out of the tap using a meat thermometer I think thermostat is bad because it is only set at A of A B C a being cooler c being hottest. I turned the power off and I'm going to replace both thermostat and the elements on Monday.

 

[GodFearinGunTotin]

I just checked on it on my lunch break, after no one being home for 5 hours, the elements were still on and I was getting a hundred and eighty degree water out of the tap using a meat thermometer I think thermostat is bad because it is only set at A of A B C a being cooler c being hottest. I turned the power off and I'm going to replace both thermostat and the elements on Monday.

You could just disconnect the power to that one element so you'll at least have some hot water.

 

[Mr Evilwrench]

I had an AO Smith that had run about 17 years and finally gave up the ghost. The one I replaced it with, I've had to put in two new lower elements in the last couple of years. I keep one on hand now. Most disappointed.

6193W is based on the 9.3Ω resistance and 240VRMS, but 9.3 may not be quite accurate. To really measure resistances that low requires a little more than just sticking an ohmmeter on them. It does give you a pretty good estimate, though.

 

[skulhedface]

6193W is based on the 9.3Ω resistance and 240VRMS, but 9.3 may not be quite accurate. To really measure resistances that low requires a little more than just sticking an ohmmeter on them. It does give you a pretty good estimate, though.

I'm confused a little. Instead of taking a known good value (240v squared) and dividing it by a questionable value (9.3 ohms) why not use the two known good values. The wattage and voltage. Which puts it in the ballpark of 11.5 ohms when good and without factoring in tolerances.

 

[K_W]

It is also not known if my line voltage is 210 or 220 or 240.

 

[skulhedface]

It is also not known if my line voltage is 210 or 220 or 240.

For mathematical purposes, it's all the same. The power is coming in to your house at 120. This connects to two lines so 240 is our number. All the other numbers are basically just different methods of averaging. So for our purposes, 220 and 240 are the same.

 

[RobbyMaQ]

It's all gobbledeegook to me but wow 180 seems really friggin high.
Ours crapped out after a year, but it was the control board and an easy fix (fancy smart heater with more bells and whistles than I can shake a stick at). I should've got gas.

 

[Brian Ski]

Sounds like the thermostat is going out. If it is getting pretty old and you are going to replace. If you have Natural Gas in your area go for that. The recovery rate is a lot faster and it is about half the price to use than electric. We have a 40 gallon power vent and it will recover as fast as one person gets out of the bathroom.

 

[remauto1187]

I'm confused a little. Instead of taking a known good value (240v squared) and dividing it by a questionable value (9.3 ohms) why not use the two known good values. The wattage and voltage. Which puts it in the ballpark of 11.5 ohms when good and without factoring in tolerances.

Because the resistance measured at the elements with a multimeter is the DC resistance....NOT AC resistance(impedance). The power supply is 240vac NOT dc. The AC would not "see" 9.3 ohms It would "see" a different value.
Have a read here: What is the difference between resistance and impedance?

 

[K_W]

New upper and lower thermostats are in.

Even after 20 hours of being turned off, and my wife taking a shower last night, the water temp at the kitchen tap was still 121 F.

I have them set to 120 and if it's still 120-130 in an hour, we are golden. I will then keep them at 130 to prevent contamination.

Thanks guys, for the help so far.

 

[Mr Evilwrench]

The 240VRMS is the equivalent of the DC value of 240VDC. You stick an ohmmeter on the element when it's cold, the resistance will not be what it is when you run that much wattage through it. It heats up, and the resistance can change quite a bit. AC or DC is irrelevant to the behavior of the element; it's the change in resistance due to heat. Impedance is a whole other issue, whether capacitive or inductive, but a heating element is pretty much purely resistive. EE here, I kinda know what I'm talking about.