Testing a Water Heater Thermostat

[Dennis Alwon]

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.

I don't think anyone is arguing this. We are all saying the same thing just in different ways. Top stat is a spdt it controls whether or not the bottom t-stat can provide heat--- I am not sure what we are arguing here.

 

[LarryFine]

On a water heater the top thermostat must be "satisfied" before the lower element is energized. Top element does most of the heating.

Not with most usage, which is less than half the tank's capacity. During wash day and bath time, maybe.

Top t-stat/element comes on first, upper t-stat gets satisfied, turns on switch to energize bottom t-stat/element.

That's true for a cold tank, not an already-hot tank during use.

 

[LarryFine]

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?

Because the upper T-stat is still satisfied, if the tank is warm enough.

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.

Exactamundo. I agree that the same thing is being said from differing apsects.

 

[LarryFine]

--- I am not sure what we are arguing here.

Who cares, as long as we're having fun. :grin:

 

[Dennis Alwon]

Who cares, as long as we're having fun. :grin:

This thread gives new meaning to talking in circles.

 

[Sierrasparky]

Ok with all that said , what causes the High limit to trip frequently with the elements checking out ok.
ie with the elements within ohms and drawing the right amps.?
No visual check of the elements.

 

[mivey]

Ok with all that said , what causes the High limit to trip frequently with the elements checking out ok.
ie with the elements within ohms and drawing the right amps.?
No visual check of the elements.

Bad thermostat or bad limit switch.

 

[G._S._Ohm]

Even at lowest setting, did not appear to be "off" i.e. still continuity.

If it's not off when submerged in boiling water at sea level it almost certainly is bad. And the T&P valve is supposed to open at less than this point.

Here's one way out of talking in circles
http://en.wikipedia.org/wiki/Truth_table

 

[readydave8]

Ok with all that said , what causes the High limit to trip frequently with the elements checking out ok.
ie with the elements within ohms and drawing the right amps.?
No visual check of the elements.

2 physical circumstances can also cause this:

1. small leak anywhere above t-stat and water running behind t-stat will cool t-stat enough to overheat water in tank.

2. same thing if t-stat is not tight against tank.

also if lower t-stat is not working properly it can overheat water.


but of course in all these cases the water is getting too hot, and kicking reset. If the reset kicks and the water is not getting too hot, then never mind.

 

[Cavie]

Ground up ground down. t-stat up t-stat down. You gotta love it.

 

[kwired]

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.

Maybe a water filter or water softener too. You are supposed to flush some water from bottom of tank periodically to help remove sediment. Most only remember this when bottom element has failed from being submerged in sediment.

I also fail to see how a "sand hog" will not fail eventually if it is submerged in sediment. The sediment will trap heat around the element and it will overheat eventually.


I have a water heater that continues to heat even if the power is off - as long as my heat pump is running.

 

[hillbilly1]

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.

Even though the elements "test" ok, the insulation integrety can be comprimised, one side of the element is always "hot", regardless of themostat position, only the master high limit kills both legs. The element can continue to heat on 120 (If the water heater is properly grounded) causing the high limit to trip.

 

[hillbilly1]

By the way, I test the thermostats by placing them on a range top eye on low heat.

 

[Dennis Alwon]

Testing elements can be deceptive if you don't disconnect the wires. I will usually disconnect one side of the element and then see if there is 120v to ground on the side that is disconnected. Then I know the element is okay. Continuity does not always work well if the element is broken and leaking thru the water.

 

[stevebea]

Ok with all that said , what causes the High limit to trip frequently with the elements checking out ok.
ie with the elements within ohms and drawing the right amps.?
No visual check of the elements.

Anyone know what kind of ohm reading should be expected on a good 4500 watt element?

 

[G._S._Ohm]

Anyone know what kind of ohm reading should be expected on a good 4500 watt element?

10% less than (240^2)/4500 ohms.

 

[kwired]

Testing elements can be deceptive if you don't disconnect the wires. I will usually disconnect one side of the element and then see if there is 120v to ground on the side that is disconnected. Then I know the element is okay. Continuity does not always work well if the element is broken and leaking thru the water.

I usually clamp ammeter on one of the leads if it is drawing near normal current it is working. If no current voltage must be verified. Voltage and no current means bad element. If element is just beginning to fail customer will not have called you for service yet. It will not take it long to fail if just beginning.

Most common failures I run into are thermostats - doesn't seem to matter as far as top or bottom they both fail frequently. Failed elements are usually the bottom one mostly because they are sitting in sediment. If a top element is failed the bottom one likely has already failed at some time before, customer likely does not use enough hot water to notice there is less hot water available because the lower one was not working.

 

[ActionDave]

Maybe a water filter or water softener too. You are supposed to flush some water from bottom of tank periodically to help remove sediment. Most only remember this when bottom element has failed from being submerged in sediment.

I also fail to see how a "sand hog" will not fail eventually if it is submerged in sediment. The sediment will trap heat around the element and it will overheat eventually.

Correct, which is the reason I maintain that if one were to think that the Sand Hog was the solution to the Water Heater Element Burning Up Because It's Immersed In Muck Blues. I would advise said person, "No it ain't. A new water heater is the only cure for what you got."

I have a water heater that continues to heat even if the power is off - as long as my heat pump is running.

How does your heat pump run with no power?

 

[hurk27]

How does your heat pump run with no power?

He lives over a hot spring

 

[ActionDave]

I know a guy that has just that arrangement.