Rheem Water Heater has me stumped!

**lizzydog** · 05-05-2009, 03:17 PM

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** · 05-05-2009, 05:38 PM

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.

**Cookie** · 05-05-2009, 05:55 PM

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** · 05-05-2009, 06:05 PM

Originally Posted by lizzydog

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 240²/4500 = 13Ω.
Voltages measured with respect to ground?

**Cookie** · 05-05-2009, 06:32 PM

12.80 you rounding?

**jadnashua** · 05-05-2009, 06:47 PM

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** · 05-05-2009, 06:48 PM

Originally Posted by Cookie

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 ±5% or ±10% this is plenty close.

We nerds get around this by using scientific notation, so 1.20 x 10² is 3 figures and
1.2 x 10² is 2 figures and 1.20000 x 10² is 6 figs.

**Cass** · 05-06-2009, 05:29 AM

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

**Thatguy** · 05-06-2009, 06:04 AM

Originally Posted by Cass

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

Rum does that to me

**lizzydog** · 05-06-2009, 01:31 PM

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

lizzydog

hj · 05-09-2009, 07:33 AM

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** · 05-09-2009, 09:16 AM

Originally Posted by hj

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** · 05-09-2009, 10:07 AM

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

**Thatguy** · 05-09-2009, 11:08 AM

Originally Posted by Redwood

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.