Nuisance electric water heater over temp trip

[rshackleford]

My hot water heater has a mind of its own.

It used to only happen when we went on vacation but now it's about every three weeks.

The water will get really hot and the over temp safety will trip. I will have to wait for it to cool and then reset. This will go on for five or six days and then stop. It will then work normally for several weeks.

It is a dual element electric.

How do I fix?

[nukeman]

Sounds like a defective t-stat. If it isn't detecting the temperature correctly or thinks the setpoint is higher than it is, the elements will continue to run and heat beyond the temperature setpoint. What ballvalve is saying is that the parts are cheap and easy to replace on an electric WH. You aren't out anything but a little time and money to replace the t-stat(s). It will probably fix it. If it doesn't, you at least know that it wasn't the cause.

An electric WH is nothing but a power supply feeding it, a couple t-stats to control the elements, usually a pair of elements for heating, and an overtemp limit trip (for safety). They are simple devices and are cheap to repair (outside of a failure of the tank itself).

[hj]

Have a plumber test ALL the components. A failing element can cause the problem, but so can a loose screw on the thermostat. IF you just start replacing parts, you may still NOT cure the problem.

[rshackleford]

How should the two thermostats be set? should they be the same or one higher than the other?

[Hackney plumbing]

If the element is grounded it can run all the time until it fails. This can/will cause the heater to over-heat and the high limit to trip. I doubt thats ur problem.

The thermostats should fit tight against the tank. The insulation should be in place over the thermostat and the exterior cover panels should also be in place.

I suggest the upper and lower thermostats match in temp settings.

You probably have a bad upper or lower thermostat.

[hj]

quote;

dying elements do not overheat, they underheat, and leak electricity into the water until they fail totally. Loose screws might cause an arc and a melt, but again it will not overheat the element itself.

Either you do not repair many heaters or you just replace everything. IF an element burns out NEAR the terminal controlled by the thermostat, it will use the water as a neutral source and heat continuously, although at a diminished rate, which is why it take longer for the high limit to trip and shut off the power. IF the screw/bolt on the high limit control is loose, the added resistance WILL overheat it and cause it to trip, regardless of the water temperature. When this happens the guilty bolt will usually change color.

[jadnashua]

IF that is so, then you still dont make it to high temp cut out. you just get a shut off at the set temp. Therefore the controls are faulty, where we started.

It's not uncommon for one leg to be connected to the heating element at all times and the other through the thermostat, and if it is working properly, no current will flow unless the thermostat calls for it. But, if there is a path to ground or neutral because it is holed, or damaged, you'll get current flow from that one leg to neutral. As said, it won't heat as fast, but it sure will overheat since it won't shut off.

[JerryR]

I think you guys stretch reality. As far as I can see the thermostat is a double make and break circuit. If you take a metal tea pot and ground it, then stick one hot lamp wire in it, you get a blown breaker.

http://waterheatertimer.org/How-to-w...ermostats.html

test your element when the thermostat is "off" NO NO NO power at any wire on the element - duh, otherwise you would have a 120 volt element that would last for years like Mr. Electricals 240 volt light bulbs. And it would heat the water perpetually. Pretty simple, Watson.

"blown elements" heat at a reduced pace until they trip the breaker BECAUSE they are 2 pole switches that break both wires. Wanna work on a water heater with one hot wire always on the element?

WRONG. WRONG. WRONG.

Look at the wiring in the link you provided.

There is ALWAYS a hot leg at each element (red and blue line in the diagram in your link) unless the OVERTEMP BREAKER POPS i.e. ECO reset trips.

In the diagram in your link;

If WH is not up to temp setting, then upper thermostat only switches left leg through T2 to upper element left screw or through T4 to lower element left screw to complete a 240 Vac across the element.

Unless overtemp reset trips, you WILL have a 120vac phase at one of the element lugs ALL THE TIME.

BE CAREFUL OUT THERE.

[hj]

quote; "blown elements" heat at a reduced pace until they trip the breaker BECAUSE they are 2 pole switches that break both wires. Wanna work on a water heater with one hot wire always on the element?

If you work on a water heater, (and I assume from your statements you have NEVER worked on, or tested, one), which has power to it, one hot wire to each element will ALWAYS be hot, because the thermostats ONLY break one leg. Other than the high limit which IS a DPST switch. I would advise you to NOT give advice regarding water heater repairs, because you WILL get someone electrocuted.

[JerryR]

I dont know what part of Bangladesh you get your heater switches from, but my meter just showed NO POWER to either element when not calling for heat.

You don’t have to get rude you know....

My GE Dual Element water heater is wired exactly like the one in your link, wire colors and all.

I just put a meter across the upper element with water heater up to temp and not calling for heat.

Across the two lugs on the upper element I read 0 VAC, i.e. element is NOT heating the tank.
BUT, When measured from either element lug to GROUND the meter reads 121 VAC...BECAUSE terminal "L4", where the BLUE and RED wires are connected, is HOT ALL THE TIME!!!!

They are single throw double pole switches.

The upper element and lower element thermostats in your link and in my Water Heater are Single POLE, Double Throw, SPDT Look at the attached diagram of the upper element thermostat you linked to and compare it to this SINGLE POLE Double Throw.
http://en.wikipedia.org/wiki/File:SPDT-Switch.svg

A Double Pole single throw has two sets of contacts that are switched like this one:
http://en.wikipedia.org/wiki/FilePST-symbol.svg

Jerry

[jadnashua]

First, you have to know how to use a multimeter! When not calling for heat, even though there is voltage applied, there is no continuity, so no current. The thermostat only opens or closes one leg of the heating element. Since it is a 240vac device, measuring across it will read zero UNLESS you connect one probe to ground, which then creates a circuit and reference for the meter to actually measure the voltage...since there's no current when off, there is NO voltage difference between the two legs of the element, but definately IS voltage from (either) leg to a ground point. And, that was the whole issue...if for some reason the element became grounded, if it didn't short out and trip the breaker, the current would always flow from the hot side to ground, increasing the water temp until the overtemp safety switch removed power from BOTH sides until reset.

[hj]

quote; First, you have to know how to use a multimeter!

No, first he has to know how to read a wiring diagram, otherwise he is going to electocute himself. He has absolutely NO idea of how water heaters are wired or HOW the thermostats work, therefore, he WILL touch a "live" circuit because he THINKS the thermostat has interupted the power.

[jadnashua]

Maybe this will help: http://eet.canton.edu/~eet/Sequence%...r%20heater.pdf

Notice that power from one leg goes to one side of EACH element (after the high temp limit switch which DOES remove power from both legs, but it's the only thing that does). The thermostat determines which element and when it applies power to the other side of the selected element to actually heat the water.

[hj]

quote; Name a 220 volt appliance that shuts off only one leg of a hot circuit. Mexico does not count.

A water heater, for one, and some baseboard heaters depending on which thermstat they use. I hate to have a battle of wits with an unarmed opponent. As the farmer said, "It doesn't do any good to wrestle with a pig, because all that happens is that you get dirty and the pig is happy". You do NOT know what you are talking about, and if the heater elements are ZERO voltage to ground then you have the only water heater in existence that way, because the upper thermostat would need SIX terminals, in additon to the ECO, and the bottom one would need FOUR of them, and YOUR heater does NOT have them, nor is there any thermostat made which is like that.

[JerryR]

Here is the sequence from Jim's link from the State University of New York, Canton, Electrical Engineering Technology Department. I highlighted the description about there ALWAYS being 120 VAC to both elements.

Notice that while Canton is pretty close to Canada, it is nowhere near either Bangladesh or Mexico.

This description agrees with my understanding of the circuit diagram and with the readings taken with my Fluke Meter.