Testing a Water Heater Thermostat

[flashlight]

Did a service call on a water heater today. ( 4500 W upper, 4500 W lower, 4500 W total, so double-throw t-stat on top) Elements tested out ok so we replaced t-stats, top and bottom.

Worked out fine, however: Could not properly test out t-stats. Even at lowest setting, did not appear to be "off" i.e. still continuity. Do I need to set them on a hot water bottle or something ?

Are there any WH mavens who can clue me in ?

Thanks !

 

[Dennis Alwon]

You need to disconnect the elements to test properly. Also the upper thermostat will always be on-- either one side or the other- it is usually a spdt switch.

If the temp in the tank is cold then it will not turn off as the lowest setting is probably still pretty high-- 100 degrees or so.

 

[flashlight]

Thanks, feel like a dummy about the first point, knew it was a spdt switch.

But I should have said ice pack instead of hot water bottle if I want to test
the lower one !

 

[GlennH]

Did a service call on a water heater today. ( 4500 W upper, 4500 W lower, 4500 W total, so double-throw t-stat on top) Elements tested out ok so we replaced t-stats, top and bottom.

Worked out fine, however: Could not properly test out t-stats. Even at lowest setting, did not appear to be "off" i.e. still continuity. Do I need to set them on a hot water bottle or something ?

Are there any WH mavens who can clue me in ?

Thanks !

What was the service call for?


typically if the reset button is tripped its because one of the tstats stuck on (usually the bottom one). Replaceing both tstats is what we do for this call.

Don't really test tstats. If the elements are ok then any temp related issues get new stats. For the price of them its not worth the time to "test" them.
I have heard of guys putting them on lightbulbs to see if they operate.

 

[flashlight]

Service call was for super hot water, followed by no hot water (limit switch tripping)

After this I agree w/ you, replace them both ($48 for the pair) if elements are OK.

 

[Dennis Alwon]

Service call was for super hot water, followed by no hot water (limit switch tripping)

After this I agree w/ you, replace them both ($48 for the pair) if elements are OK.

These symptoms are diagnostic of the upper stat malfunctioning. The bottom stat rarely goes bad. I have replace just the upper stat and generally the water heater goes bad before the bottom stat malfunctions.

 

[ceb58]

I hope that when you left the job the thermostats were set to the lowest setting.

 

[GlennH]

These symptoms are diagnostic of the upper stat malfunctioning. The bottom stat rarely goes bad. I have replace just the upper stat and generally the water heater goes bad before the bottom stat malfunctions.

Don't agree. Cold water enters through tube to bottom of tank , when hot water is used cold water cools bottom of tank first bringing on bottom element. VAST majority of heating is done with bottom element. I rarely find the top element or thermostat bad, once in a while but not often.

 

[Dennis Alwon]

Don't agree. Cold water enters through tube to bottom of tank , when hot water is used cold water cools bottom of tank first bringing on bottom element. VAST majority of heating is done with bottom element. I rarely find the top element or thermostat bad, once in a while but not often.

You can feel free to disagree but you cannot deny my experience. I am not sure I ever replaced a bottom thermostat and have replaced many upper stats.

I agree the water goes to the bottom but if the top of the tank calls for hot then it will turn off the bottom and start heating the top. During heavy use the top element is on very often. Priority is set for the upper part of the tank.

 

[flashlight]

Yes, I did leave the settings low-- they can scald themselves on their
own dime !

 

[ActionDave]

You can feel free to disagree but you cannot deny my experience. I am not sure I ever replaced a bottom thermostat and have replaced many upper stats.

I agree the water goes to the bottom but if the top of the tank calls for hot then it will turn off the bottom and start heating the top. During heavy use the top element is on very often. Priority is set for the upper part of the tank.

I agree with Dennis with one exception, a water heater on a well can fill up with a bunch of muck that can burn out the bottom element. My local hardware store sell a special element called the "Sand Hog", but if you need one of these what you really need is a new water heater.

 

[muskrat]

I agree with Dennis with one exception, a water heater on a well can fill up with a bunch of muck that can burn out the bottom element. My local hardware store sell a special element called the "Sand Hog", but if you need one of these what you really need is a new water heater.

Read the instructions---drain water and "muck" out bottom drain once or twice per year. More if neccessary. Inform HO
watt-hour meter on dual-element water heater showed lower element/stat did 90% of work(would depend on # in household)
some areas w/ hard water require changing elements to lower wattage to prevent build-up of scale in bottom of tank
thermo-disc on back of stat can be tricked to turn off/switch elements by gently heating w/ lighter
if overload is tripping, change it

 

[haskindm]

On a water heater the top thermostat must be "satisfied" before the lower element is energized. Top element does most of the heating. Bottom elements usually burn out because they get covered with "muck" and then overheat.

 

[mtfallsmikey]

Musings from the house plumber...

Musings from the house plumber...

On a water heater the top thermostat must be "satisfied" before the lower element is energized. Top element does most of the heating. Bottom elements usually burn out because they get covered with "muck" and then overheat.

Top t-stat/element comes on first, upper t-stat gets satisfied, turns on switch to energize bottom t-stat/element. Most newer water heater 'stats are junk, can be as much as 15 deg. from where you set them. The old Robertshaw AW series were the best, no longer made. If possible, I lift the stats out of the holder so I can get to them with a heat gun to test them, but there is no "off" position, per se, but if the elements check ok (amp test, not resistance), then it's best to replace both 'stats. It will save a callback.

 

[muskrat]

On a water heater the top thermostat must be "satisfied" before the lower element is energized. Top element does most of the heating. Bottom elements usually burn out because they get covered with "muck" and then overheat.

wrong-when tank is completely warm/all elements off-hot tap on, cold enters botton of tank via dip tube, lower element comes on. If continuing to draw hot water and lower element isn't satifying demand, upper stat shuts off lower and energizes upper ele. as hot is drawn from top of tank

 

[Dennis Alwon]

wrong-when tank is completely warm/all elements off-hot tap on, cold enters botton of tank via dip tube, lower element comes on. If continuing to draw hot water and lower element isn't satifying demand, upper stat shuts off lower and energizes upper ele. as hot is drawn from top of tank

That is what Haskindm was saying so why are you saying that it is wrong? Last 3 posts are all saying basically the same thing..

 

[mtfallsmikey]

With the cold water enteriing the heater at the bottom via the dip tube, if the lower t-stat came on first, how would the 'stat ever get satisfied? The upper 'stat does not control the lower stat temps, but switches on the power to the lower stat when the upper stat's temp. is satisfied. Some models used to, and can be set up for simultaneous element operation.

I know I'm inexperienced, just been installing and servicing water heaters for only 35 yrs.

 

[mtfallsmikey]

We're all kind of right, and wrong...

We're all kind of right, and wrong...

Let's put this in our pipes and smoke it...

http://eet.canton.edu/~eet/Sequence hot water heater.pdf

 

[muskrat]

That is what Haskindm was saying so why are you saying that it is wrong? Last 3 posts are all saying basically the same thing..

Just saying lower element does most of the work.
And all replying at the same time.

 

[Electric-Light]

Water enters at bottom by a tube that extends down and hot water exits out the top.

Upper element is always on when it is cold. When it gets hot, SPDT transfers power over to bottom thermostat.

When hot water is used, the bottom element fires up almost right away heating the cold water as it is filled from the bottom. The top element only fires up if you deplete enough of the stored water to drop the top part below the set temperature.

mid-range electrics often have stainless/incoloy on just the bottom while the top is copper.