Rheem Hot Water Tank w/cold water

[dgail620]

Last night while doing dishes, noticed that the water was unusually hot out of the tap. I've previously (at least a year ago) taken out the elements and thermostat on the hot water tank because I've never felt the water was hot enought out of the tap (set at slightly over 125 degrees on the tank). They tested out okay, but since I had the part, I went ahead and replaced it.
This morning guess who got a cold shower?
I set the reset button tonight, and the tank immediately started heating up.
I know I didn't fix the problem, it shut off for a reason. Where do I start? Sounds like it may be an thermostat to me, and I do have a multimeter and found the directions in a search to test it. Is that where I should start, or am I barking up the wrong tree? Bad element?
For the record, I have a double element non simultaneous operation thermostat. The water heater has the combination Thermostat and Temperature Limiting Control (ECO) which shuts the power off to the element if the temperature becomes too high, which it what it did.
Where do I start?

[LazyPup]

You may not have a problem at all. According to the heading on your post you live in the Dallas, Texas area and out of curiosity I did a quick search of the current weather characteristics in Dallas, Texas. While your daytime temperatures have been rather mild your night time temperatures have been dipping into the upper 40's.

From a personal knowledge of building techniques I know that a large portion of the homes in your region have electric heat or use heat pumps, which also operate by electric. This means that when you get a cold snap the load on the local power grid is maxed out. This often results in a temporary "Brown Out" which is a slight reduction in line voltage brought on by the excess load.

Wattage is determined by multiplying Voltage x Amperage. The problem here is that the wattage of a resistance element will remain nearly constant even when the voltage is altered, therefore in order for the wattage to remain constant, if the voltage drops there is a proportionate increase in the amperage draw.

The overload protectors built into water heater thermostats are critically matched to the amperage requirements of a water heater under normal operating conditions and occassionally they will trip out during periods of Brown out or reduced line voltage.

Based upon the information in your post this has only occured one time in the last year so it may not be a problem at all. You stated that you reset the overload protector and the water heater instantly began working again so all indications are that the tank is working fine. I would hold off for now, but if the water heater trips out again within a short time then it would merit doing a full diagnostic on it.

[Phelps]

LazyPup,

But isn't the fact that he had extra hot water come out of the faucet indicative of a stuck stat? The internal points get burned and can act sporadic... which one moment causes them to literally fuse together, causing the water to get very hot... and then for another cycle, the points may not even make good contact with each other at all at those scorched/pitted points. I have busted open plenty of sets of (especially lower stats) to see what happened to them, and found them to look like the old car points when they would go bad.

[LazyPup]

Sticking contacts is also indicative of a low voltage condition. If it only occurred one time odds are there is no permanent damage to the contacts, that is why I suggested just resetting and letting it go for the moment but if the problem persists we will need to go into a full diagnostic on the control system,

[dgail620]

yet again

Well, tried the hot water this morning, and it seemed again to be a little hotter than usual. I left the water running for about 10 min, washed a load of warm in the washer, and waited a bit a took a shower. A cold one. The reset button was again able to be reset. Something is throwing it.
Where do I begin?

[LazyPup]

When a water heater overload trips out once it might be a low voltage brown out but that is highly unlikely to happen two days in a row so let us proceed to diagnose the heater.

You stated in your previous post that you have a multimeter so I will assume for the moment that you have at least a fundamental knowledge of electrical troubleshooting.

Begin by disconnecting the electrical service at the circuit breaker or the service disconnnect. Both the Plumbing Codes and the National Electrical Codes require that if the circuit breaker is used as the primary disconnect there must be either a direct line of sight from the water heater location to the service panel or the service panel must be equiped with a lockable cover. If not, we are required to install an electrical service disconnect in the near proximity of the water heater. Even though this is a current code requirement many in homes the system was installed before these requirements were written into the code. If your water heater uses the circuit breaker, and if there is not a direct line of sight from the breaker to the water heater for your own personal safety you should inform the other members of your household that you are working on the water heater otherwise someone might not know and they could mistakenly turn the breaker on while you are working. (I personally prefer to hang a large note on the front of the breaker panel informing people not to turn anything on).

The electrical overload protector has tripped out two days in a row so this is indicating there is some condition with this water heater that is causing an excessive amperage draw. There are primarily only two conditions that will cause this to happen, either low voltage or both heating elements are attempting to work at the same time.

Begin by visually examining the electrical service cable to the water heater, especially at the point where the cable enters the water heater enclosure. If you see any signs of discoloration or the outer sheathing of the cable discolored it may be indicating the cable has been overheating. (For a 30amp service the cable should be AWG 10 wire.)

On the top of the heater directly beside where the electrical cable enters the heater cover you will see a small service access cover. Remove the cover and examine the wire connections. Any loose, corroded or burned connection would result in a voltage loss, thus causing an increase in amp draw. If all the connections are good replace the cover then remove the upper service cover on the side of the water heater where you have previously pressed the reset button.

It is very unlikely that you have any problems with the heating elements but just to be sure let us check them out.

Typically the heating elements in an electric water heater draw 4500watts.

Watts equals amperage x voltage so we can estimate the amperage draw by dividing the wattage by the listed supply voltage.

4500watts / 220volts = 20amps.

OHMS LAW states that E= I x R
where E = Electromotive Force (Volts)
I = Inductive Force (Amps)
R= Resistance.

If E= I x R then R = E / I

thus R (resistance) = E (240v) / I (20amps)
R = 12 ohms

This means a good heating element should show approximately 12 ohms of resistance.

Whenever we are testing a component with an OHM Meter it is important that we isolate the component otherwise the meter might be measuring through the wiring to other components and cause a false reading.

Begin by removing one of the wires from the heating element then set your multimeter on an OHM scale. Most meters have multiple scales for OHMs. select a lower scale that would put the theoretical reading about mid scale on your meter. (20 to 50 ohm scale)

If you have an analog meter (mechanical needle type) you will need to first calibrate your meter. To calibrate touch both the test lead tips together and turn the calibrate knob until the needle is centered on ZERO on the scale.

Now touch one probe one tip on one of the electrical terminals on the heating element and touch the second probe tip on the opposite terminal and check the reading on the meter scale. NOTE: in the real world electrical components will seldom read exactly what the theoretical reading was. If the reading you get is the same as the theoretical reading or +/- 10% its okay.

If the reading is ZERO OHMS the element is burned out and will need replacing.

If the reading is INFINITY (full scale on the meter) the element is shorted out and will need replacing.

After you have finished testing the element re-connect the wire you removed, then open the lower service cover and check the lower element in the same manner.

At this point we have completed all the tests we can do with the power off.

The preferred instrument to perform powered operational testing would be a snap on amp meter but they are fairly expensive and it is highly unlikely that a homeowner would have one. We are then left with two options:

1. You could turn the power on and turn the thermostat temperatures up about 10 degf to make sure the unit will begin the heating cycle.

With your multimeter set on the VOLTAGE SCALE measure the voltage on the termininals of the upper heating element. You should get a reading on the upper heating element somewhere between 220 to 240volts and zero volts on the bottom element.

Now open a faucett and run the hot water about 5 minutes and check the voltage on the bottom heating element again. When you get a reading of 220 to 240volts on the bottom you should get a reading of Zero on the top element.

If at any time you get a reading of 220 to 240 on both elements at the same time the upper control is defective and will require replacing.

If you do not feel comfortable with making live powered tests the alternative is to replace both the thermostat controls. The good news here is that they are inexpensive and very easy to change.

As an example, i just checked my Home Depot catalog and they show the ThermoDisc replacement upper thermostat @ $12.08 and the lower thermostat @ $8.47.

Both the thermostats are quickly mounted by snapping into a spring steel retainer clip and connect the wires. A word of caution here though-Not all of the upper thermostats have the same pin configuration on the wiring so be sure to check the wiring diagram on the new thermostat package when installing replacement thermostats.

[dgail620]

Exactly what I needed....

Thank you so much for taking the time to explain in great detail exactly what I needed to know.
My box is outside on the side yard, and it's raining cats and dogs right now, so I will wait for a break in the rain to run out there and hit the circuit breaker and chase this down.
I think the lower element may be the suspect, as it's the one I didn't replace last year, but I will check them both. I have a Home Depot 5 minutes from me, too.
Again, thank you, and I will let you know what I find.

[dgail620]

aha...

It appears it is the lower element, no reading on it at all. Also, I noted the wire is a little scorched looking that connects to one of the terminals. I guess this means I get to drain the tank and replace the element.
I think I'll wait until this barrage of rain lets up.

[LazyPup]

Here is an easy procedure for draining the tank...

1. Make sure the power is turned off

2. Connect a garden hose to the drain valve and run it outside or to a floor drain.

3. Open the tank drain valve and allow the water pressure in the tank to force the water through the hose until it begins discharging out of the hose, then close the cold water valve to the water heater.

4. Open a hot water faucett to allow air to vent into the hot water lines to aid in draining the tank.

If you follow these steps the tank will drain much faster than just attaching a hose and opening the drain valve.

If you have the type of heating elements that are held in by a flange with four bolts they are fairly easy to remove and change.

If you have the screw in type they can be a real pain to remove. You will find an inexpensive water heater heating element socket wrench in the hardware stores that will remove them but it can be rather fruststrating. If you happen to have an 1-1/2 Socket with a 3/4" drive ratchet or a breaker bar you will find that is much easier to use.

One word of caution when removing screw in elements. The sheet metal enclosure covering the water heater can have some fairly sharp edges and when using the cheaper element removal socket they tend to slip off the element very easy. Be sure to wear some good heavy leather gloves while removing the heating element so that if the wrench slips and your hands hit that sheet metal you will not get cut.