testing thermostat

I have a 2 element water heater and i wanted to test the thermostat to be sure it was working properly. I check the heating elements and they are good. The reason being is that i got call about the water would be hot for about 15 minutes then it cools off. Even though i think the 'complaining' person is just being PICKY, I want to check everything before i start buying new parts.

Its my understanding that the upper and lower thermostat do not come on at the same time. I check the voltage and voltage is good. the top thermostat was on, but the bottom wasnt. Is there a way i can test it or make it come on without have to move wires around?? Thanks

brother said:

... i got call about the water would be hot for about 15 minutes then it cools off.

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What size is the water heater, what is its temperature setting, and what kind of fixture or fixtures are being run during that 15 minutes?

If the heater is small and/or the setting is low and/or the dishwasher and shower are being run at the same time, that 15 minutes might just be all the heater has to offer.

filling a tub can empty a WH.

Need more information.
Size etc
Usage etc

Are they leaving the HW tap open most of the time?


david

A 50 gallon electrice heater has a first hour delivery of about 60 gallons ( 70% rule + recovery). The short term delivery is about 35 gallons of water hot enough for a shower. 35 gallons divided by 2.5 gpm is about 14 minutes. As Jack Nicholson says, this is about as good as it gets.

Great movie Jim. Sometimes ain't it the truth, lol.

I had a person with the same complaint once after a well known store installed a new tank and they had hooked up the hot to the cold and the cold to the hot. They wouldn't change it because they said it didn't matter, I changed it and solved the problem.

brother said:

Its my understanding that the upper and lower thermostat do not come on at the same time. I check the voltage and voltage is good. the top thermostat was on, but the bottom wasnt. Is there a way i can test it or make it come on without have to move wires around?? Thanks

Click to expand...

Yea, turn the upper all the way down and wait for it to satisfy and check that it switches... Its a lot quicker waiting for it to satisfy at the lowest setting. I also like to use a clamp on amp meter to test elements.

geniescience said:

filling a tub can empty a WH.

Need more information.
Size etc
Usage etc

Are they leaving the HW tap open most of the time?


david

Click to expand...

This is a 50 gallon, 4500 watt water heater . I believe they use it pretty regular. its a 2 bed room house but only 1 person lives there. Ill double check the thermostat again tomorrow. I found more info on testing it, however something tells me its just this person wanting too much. The temperture is set at 120 degrees on both thermostats. Yes they do use alot of hot water.

Usually when an element is bad, the water doesn't get very hot or it trips the breaker.

When a thermostat goes bad, the water is often scalding hot, no matter what temp. it is set on.

If he had plenty of hot water before this, I would check the diptube. A broken diptube will drastically reduce the amount of hot water.

If he's always had this problem, just turn up the thermostat to 140.

Wh

At 120 degrees a shower is using almost all hot water with maybe a little cold water mixed in. At that rate a shower will deplete it in a very short time.

Brother said:

I check the heating elements and they are good.

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I'm curious as to how you did that.

Here's how I do it -

1) check incoming power.
2) check that there's power to one element
3) feel the tank next to the bottom element
4) turn off power - remove wires from elements - check for continuity

Now - those steps are great, but the won't tell you everything. Just because an element shows continuity through the calrod and not from calrod to to tank does not mean that the element actually works, though it's good most of the time.

If the bottom of the tank is hot, it's a pretty good indication that both elements are working because the bottom one shouldn't come on until the top one is hot. (Though even this can happen with a stuck top t-stat.)

If everything tests good and the tank is hot to the bottom but the cold starts coming through soon after turning on the water, then it's time to check the dip tube, or a cross-connection in the building, such as a failed Moen 1225b.

And just because a thermostat is set at 120 does not mean that it will accurately produce 120 degrees. Either the thermostat could be inaccurate or it might not be working properly.


Upper Thermostat



Bottom thermostat

Herk said:

I'm curious as to how you did that.

Here's how I do it -

1) check incoming power.
2) check that there's power to one element
3) feel the tank next to the bottom element
4) turn off power - remove wires from elements - check for continuity

Now - those steps are great, but the won't tell you everything. Just because an element shows continuity through the calrod and not from calrod to to tank does not mean that the element actually works, though it's good most of the time.

If the bottom of the tank is hot, it's a pretty good indication that both elements are working because the bottom one shouldn't come on until the top one is hot. (Though even this can happen with a stuck top t-stat.)

If everything tests good and the tank is hot to the bottom but the cold starts coming through soon after turning on the water, then it's time to check the dip tube, or a cross-connection in the building, such as a failed Moen 1225b.

And just because a thermostat is set at 120 does not mean that it will accurately produce 120 degrees. Either the thermostat could be inaccurate or it might not be working properly.

Click to expand...

I had power at the heating elements. in fact i drained all the water out of the water heater, and removed the heating elements and checked them that way. They looked good and had good continuity. Usually when my heating elements go bad, they go completely bad, they break inbetween.
Also when i turned on the water the temp seemed fine, in fact it almost burned my hand. I dont think i tested the thermstat correctly so i will double check. But if that turns out ok, then i think this is as good as it gets!!

In this state we HAVE to keep the water heater at 120 degrees. also HOW do you replace or check a DIP TUBE??? Or is it even replaceable.

Brother said:

I had power at the heating elements. in fact i drained all the water out of the water heater, and removed the heating elements and checked them that way.

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What kind of power? You should find 120 at each element, or 240 at the one that's currently powered.

Did you check the bottom of the tank after it hadn't been used and see if it was hot to the bottom? I'd never drain a tank and remove the elements if it was heating to the bottom of the tank unless I knew the sediment needed cleaning.

In this state we HAVE to keep the water heater at 120 degrees. also HOW do you replace or check a DIP TUBE??? Or is it even replaceable.

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I was unaware that any states were requiring that. I can see a plumber's insurance company insisting on it, but that really seems like government intrusion.

Dip tubes normally pull out if you remove the nipple/heat trap on the cold side.

You'd probably find that the requirement is that the water temperature outlet must be no more than 120-degrees. You could run the tank at 140 or even higher and then run it out through a tempering valve that reduced it to 120. This would let you store more equivalent hot water in the same sized tank (at an increase in energy). There has been a requirement where I live to install a tempering valve on all new or replaced tanks. I can run the actual tank temperature anywhere the controls will allow (nominally I keep it at 140).

water heater elements

To check out the thermostats....

you have to actually take the thermostats
off the heater and put them against a hot light
bulb to make them click on and off.....

and you have to wire up the t-stats to a ohm meter to
see if they actually switch the circuit...

its a lot of trouble


you could also have a grounded out element...which is very
hard to detect....

as much trouble as you already have gone through
might it not be easier to just change the parts??.

master plumber mark said:

To check out the thermostats....

you have to actually take the thermostats
off the heater and put them against a hot light
bulb to make them click on and off.....

and you have to wire up the t-stats to a ohm meter to
see if they actually switch the circuit...

its a lot of trouble


you could also have a grounded out element...which is very
hard to detect....

as much trouble as you already have gone through
might it not be easier to just change the parts??.

Click to expand...

Well im done, the thermostats checked good, and i let the water run from the sinks for a good 20 min. Its still hot . I think the person complaining was just wanting too much. The reason i went ahead and drained it the first time was because its been a while since the water heater had a good draining, try to get rid of some of the sedement at the bottom.

Also i like to KNOW WHY something is not working right instead of just changing the parts, especially since it might not be a problem at all. Thanks for the help.

master plumber mark said:

you could also have a grounded out element...which is very
hard to detect....

Click to expand...

If you don't have an ohm meter very difficult!
If you do have an ohm meter and know how to use it the hardest part is taking the cover off the water heater.