Rheem Water Heater has me stumped!

lizzydog · May 5, 2009

Heater 3yrs old
electric
30 amp double pole breaker
120 volts each leg breaker
120 volts each wire at heater
new thermostat
new elements
120 volts each side thermostat
120 volts each side of top and bottom element
reset pushed
NO Hot Water
Help

Thanks
lizzydog

Jimbo · May 5, 2009

Measuring each leg of a 240 volt circuit, to ground or neutral, will throw you off. You never know when you are reading across an open.

You need to see 240 across the two terminals of an element. If it is not 240, it will not heat....period. Something is open.

Sponsor · 2022-01-29T12:20:58-0800

Cookie · May 5, 2009

Try turning the breaker all the way off and then, all the way back on. Check the top 2 scews of the top thermostat at the same time and you should have 240 volts.

Thatguy · May 5, 2009

lizzydog said:
120 volts each leg breaker
120 volts each wire at heater
new thermostat
new elements
120 volts each side thermostat
120 volts each side of top and bottom element
reset pushed
NO Hot Water
Help

Thanks
lizzydog

Each 4500w element should read 240Â²/4500 = 13Ω.
Voltages measured with respect to ground?

Cookie · May 5, 2009

12.80 you rounding?

Jadnashua · May 5, 2009

Well, few meters out in the field can read that accurately, plus, the resistance will be different than that when cold verses energized...but, close enough.

Don't try measuring resistance with the power on unless you like sparks and value the meter (the fuse should blow, but you never know).

Thatguy · May 5, 2009

Cookie said:
12.80 you rounding?

That I be.

There is also Significant Figures, which is a little harder to 'splain.

120 could mean between 119.5 and 120.4 [3 significant figures] or it could mean 115 to 124 [two significant figures] in which case the '0' is just a placeholder. I took it to mean two figures and so the answer should be the same number of figures. Since the 120 varies by Â±5% or Â±10% this is plenty close.

We nerds get around this by using scientific notation, so 1.20 x 10Â² is 3 figures and
1.2 x 10Â² is 2 figures and 1.20000 x 10Â² is 6 figs.

Cass · May 6, 2009

WoW...were trying to fix a water heater not fly to the moon....

Thatguy · May 6, 2009

Cass said:
WoW...were trying to fix a water heater not fly to the moon....

Rum does that to me

lizzydog · May 6, 2009

Rheem waterheater has me stumped

Thanks for all the information. The new 30 amp double breaker was bad.

lizzydog

hj · May 9, 2009

heater

WHO measures resistance? If the element has 240 volts and the amperage is ZERO the element is bad. It it reads in the neighborhood of 18 amps it is good. AND both leads have to read the same amperage.

Thatguy · May 9, 2009

hj said:
WHO measures resistance?

Nah, he's on first

I figured more people have ohmmeters than clamp-on ammeters and more people prefer to make unpowered measurements.

240v/18A = ~13Ω.

Redwood · May 9, 2009

I test like HJ does...
Seems to work for some reason...

Thatguy · May 9, 2009

Redwood said:
I test like HJ does...
Seems to work for some reason...

What's also is in your favor is that a water heater element doesn't fail in many different ways.

I doubt that the element resistance changes in value and it's unlikely that the resistance element shorts to the grounded element tube because of all that ceramic insulator packed in there, so your choices for resistance/current flow are 13 Ω/18A or infinity/zero.

It's pass/fail.

Redwood · May 9, 2009

Oh elements do short to ground.

Thatguy · May 9, 2009

Redwood said:
Oh elements do short to ground.

In that case troubleshooting by CB is easy!

The ratio of failing by opening to failing by shorting is, would you say, 90/10? 60/40?
I don't fix enough of these to offer odds.

Redwood · May 9, 2009

Thatguy said:
In that case troubleshooting by CB is easy!

Not always.
Lets say the short occurs at the center of the element.
The element will coninue to work normally without popping the breaker however, since only one side of the power is switched by the t-stat the element will continue to heat on 120 volts after the t-stat shuts off.

The hot water if not used will end up being quite hot...

This is the reason for checking both wires to the element for amperage to make sure they match.

Rheem Water Heater has me stumped!

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