On Sun, 17 Feb 2008 02:03:48 GMT, Reinhard wrote:


The lower wire block has 2 screws - black wire in and a black wire to the
element.

I downloaded the manufacturers wiring diagram and the connections match
the diagram. Worked fine for over a year so I assume connections are OK.

Can someone explain how to test and determine which thermostat is bad? Or
could there be a bad element?

Can you close off the output from one tank at a time and see if the
other tank is putting out hot water? They might both be, but if not,
that would be a big clue. Or close the input to one tank.

Of course there could be a bad element. My impression of my WH is
that there was no need to disconnect any wires from the elements to do
a good measurement of the resistance, but certainly in some things,
like radio where parts are in parallel, that isn't always true. you
should re-examine the wiring diagram to make sure there isn't some
alternate path that would make an open element look like a working
one.

In my case, and yours since like mine, there are also only two wires
going to the bottom thermostat/element combo, it will be easier to
measure the bottom than the top. If no one has used hot water for an
hour, the water should be hot and the lower thermostat should be open.
Turn off the power and with the meter on 240AC or higher, measure for
AC voltage across the thermostat. Yes, I know I just told you to turn
off the power, but some day you will forget to do that. If you
attempt to measure resistance when the power is still on, you'll
likely burn out your meter, if nothing worse. So always measure for
voltage before measuring for resistance.

When there is no voltage, measure the resistance across the
thermostat. It should be infinite, meaning that it is open and that
means one of the leads from the lower element doesn't connect to
anything now. So now you can measure the resistance of the lower
element without there being an alternate path, and you will get a
correct reading. Anything lower than infinity is likely to be good.

Also measure the resistance from the ground wire or the metal case of
the water heater to each of the wires on the heating element. It's
possible for the element to short against, I guess, the element cover,
and to make the case "hot". If so, the element has to be replaced. If
the element is 14 ohms, then whatever the resistance between one of
the screws and the case is, unless it is infinite (as it should be)
the resistance between the case and the other screw should be 14 ohms
higher, or lower.

Thanks,

Reinhard

I'm nowhere near a pro, but aiui, in a some wheaters the upper and
lower elements might run at the same time, but I think in most, the
upper element runs first to provide some wh at the top of the tank and
when it heats up a little, then the top thermostat sends the current
to the lower element which does most of the heating. The lower
thermostat turns that one off when the whole tank is hot enough.

Doesn't it say on the manu. wiring diagram something to indicate which
kind of system you have? The kind you have will determine what you
should look for.

My last wh had an LED connected across the upper element, so that one
could easily tell when it was on. (at least when there was power to
it. That didn't mean the element was working, but I never had doubts
that it was.) I was thinking of putting an LED across the bottom one
too this time, because I've had some of the same questions you have
now**. You probably don't have room for these when the covers are on,
but you could, when the power is off, connect lights like this
temporarily and see when power is going to each element. LEDs for AC
may be different from those for DC, i don't remenber. But the rating
will include 240 volts AC.

Or you can very carefully use a meter. I would, when the power is
off, make sure that the insulation isn't in the way of making
measurements, and for the lower element, I would sit on the floor so I
didn't fall over and fall into the waterheater. I would even consider
using jumper wires with alligator clips on both ends and connecting
these to the meter probes and the screws when the power is off, then
turning the power back on. I assume you are well acquainted with the
precautions you need for 240 volts. It's much more dangerous tan 110.


**But the new styrofoam? insulation around the thermostat left no easy
room for even the one LED, so instead now I have none.