The Tank › tripped high temp and breaker
- February 5, 2011 at 6:38 pm #15140
I have a 2 element electric water heater. About a month ago the high limit tripped. I reset it and it has been fine until today when we awoke to no hot water. The breaker was tripped at the breaker box. I reset it and monitored the voltage on the tank. The top element was at 220 at first and the bottom at 110. After a bit the top went to 0 and the bottom went to 220. I believe this is normal.
I have continued to monitor it and after a couple of hours the bottom element has never shut off, or if it has it wasn’t for very long. I ran some hot water into the sink and the top element went back to 220 for awhile and the bottom element went to 110. After a few minutes it returned to 0 top and 220 bottom. Now another awhile later the bottom element is still showing 220 everytime I check it.
It seems like the top element and thermostat are functioning properly from what i have read here but I am concerned that there is a problem with the bottom element, thermostat, or both.
I should add that we have very hard water and it has been a couple years since the bottom element was changed and the element replaced. So what is your advice. Drain the tank, clean out the calcium, and replace both the element and thermostat, replace just the element, or just continue to monitor it.
Thanks in advance for any help and also for such a helpful site.February 6, 2011 at 6:39 am #15145
Sounds like the top thermostat is good.
The high limit will trip when a thermostat fails to open or you get a crack in an element. As you noticed the thermostat only opens one leg so a cracked element lets the non interrupted leg continue to supply power to the cracked element which completes its circuit to ground through the crack through the water to the tank wall and continues to heat though at a very slow rate.
Entering “The Tank” you will find “Tanklets” at the top. Go to Electric WH Issues. There you will find guidance on using your volt-ohm meter to check the elements.
The lower tstat should cycle open if you wait long enough or you could just lower the setting after say 30 minutes of no HW use and see if it opens. If it opens you should have only the 110 volts you had as when the top tstat was supplying power to the top element.
DavidFebruary 6, 2011 at 9:27 am #15147
Thanks for the reply. I can’t believe I didn’t think to turn the thermostat down. I’ll check it out and post what I find.February 6, 2011 at 2:09 pm #15151
I turned both thermostats up and didn’t use the hot water for a couple hours. Then I turned them down and the lower one still wouldn’t shut off.
I checked both elements and the lower one is bad. It doesn’t have continuity from terminal to terminal and it does have some when I check from either terminal to the flange.
It is draining now and I will clean out the sediment and change the element. My only question now is should I go ahead and change the thermostat while I have it drained or just change the element. I have not changed a thermostat before so is it very involved?
Thanks again for all the help.February 6, 2011 at 2:53 pm #15152
I hope you did remember to turn off the power before draining. If not you will also have burned out the top element.
Thermostats. Usually a piece of spring steel is pressed over the element nipple. Two fingers of this steel engage the front of the tstat on each side and keep it pressed back in contact with the tank wall. Just dewire the tstat and wiggle it up. When installing the new one just don’t pull the fingers out too far or you can bend them so they don’t press the tstat against the tank.
If you look at the picture posted in “Electric WH Issues” of the tstat you can sort of see the spring steel behind the polyethylene.
Have water running out a hot tap before turning on the power.
DavidFebruary 6, 2011 at 9:33 pm #15155Randy SchuylerKeymaster
Just for what it’s worth: if the heater is older than six years, think about checking and replacing the anode. People have trouble differentiating function from longevity. If it functions, they think everything is OK. The longevity is a separate issue, but one you need to think about, too.
Randy SchuylerFebruary 7, 2011 at 9:59 am #15156
Thanks for the help again. It turns out only the bottom element was bad. I replaced it and everything works normally now. One thing I do not understand though, maybe somebody can explain to me.
Before replacing the bottom element when the top element was heating I had approx. 240volts at the top element and approx. 120volts at the bottom element. Then when the top thermostat switched over I would have 0 volts at the top and 240 at the bottom.
After I replaced the bottom element, when the top element was heating I still had 240v at the top but 0 volts at the bottom. When the top thermostat switched over I had 0 at the top and 240v at the bottom.
Any ideas why? To be clear, all I did was replace the bottom element. I did not mess with the top one or either thermostat.February 7, 2011 at 1:01 pm #15157
When the tstat is closed and the element is good or bad you will read 240 volts across the element (screw to screw).
When the tstat is open and the element is good you will read 0 volts across the element (screw to screw) but 120 volts on either screw to ground. Voltage feeds through the element.
When the tstat is open and the element is open (and the sheath cracked through to the water) you will read 120 volts across the element (screw to screw) but 120 volts on one screw to ground and 0 volts screw to ground on the other screw.
DavidFebruary 18, 2011 at 6:39 pm #15274geno03245Participant
Some water heater manuals say that if factory-supplied insulation and cover are not in place that thermostat will not read correct temperature because thermostat is exposed to cool air. This would cause element to continue heating and possibly cause overheating event.February 18, 2011 at 7:42 pm #15277Randy SchuylerKeymaster
I expect they ALL say that — and we say it here, too. That’s one of the tricky things about do-it-yourselfers. If they don’t put everything back in the element port the way it was, they may cause the heater to malfunction.
- You must be logged in to reply to this topic.