Water Heater Pulling 18 Amps Continuously - Not Heating

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Old 04-16-14, 03:04 AM
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Water Heater Pulling 18 Amps Continuously - Not Heating

Been doing plumbing and electrical work for nearly 40 years and here is a new one for me.

50 gal elec water heater, maybe 3 years old. Rated 4500w

It is pulling 18a on both hot wires supplying the heater so that's at 230v, measured by an Amprobe.

There is no leak and the T&P is not leaking either.

One wonders how a heater can draw it's rated current and not heat water.

Elements test ok. Resets are not tripped.

I know there can be issues with broken dip tubes and cross connections, but can't really see how either could apply here.

I also know that the situation I describe should be a physical impossibility, as current drawn is current used, and will yield an equivalent amount of heat into that water!

Tips appreciated


Water Heater Pulling 18 Amps Continuously - Not Heating
 
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Old 04-16-14, 06:02 AM
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Is any fixture (or washing machine) running water from the hot water plumbing? All-electric water heaters heat water quite slowly so when starting from a cold tankful, you will never get hot water if the water is running continuously more than a trickle.

You're sure there are no leaks in the plumbing, no? (Hard to verify if you have piping in a slab floor.)

Verify that the hot water plumbing is air-free (run a hot water faucet for a full minute) Then turn off the water heater cold inlet valve above and let the water heater heat for 4 hours.

Then open the cold inlet valve again and run hot water for 30 seconds. Feel the water heater hot outlet pipe. Is that warm?
 
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Old 04-16-14, 06:07 AM
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I hope you are seeing 240 volts, the standard voltage in the USA and Canada and not 230 volts.

My first guess is that you are somehow measuring incorrectly. Amprobe is a brand. What type of amp tester are you using and how are you using it? Does it clamp around the hot wires? Or do you connect your meter in line with the circuit? Do you ever read other than pulling 18 amps? What if you adjust the thermostats all the way to their minimum can you get them to click off and stop pulling current? Disconnect the heating elements and see if you still show an 18 amp draw.
 
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Old 04-16-14, 06:14 AM
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Trick question. Which water heater element is drawing power (upper or lower). Hint: "Both" indicates a malfunction or an incorrect measurement regardless of the number of amperes respectively.

You are correct that is is a physical impossiblity for a water heater to draw significant power and not heat something noticeably. (You should feel around cautiously to be sure there isn't a not-so-short circuit causing a fire hazard inside the water heater unit but outside its tank.)

Measuring a different voltage but reasonably close to 240 is not a concern for this question.
 
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Old 04-16-14, 10:05 AM
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Alan was dead on the money! thanks (also it was heating on the top element). A.O. Smith specs say that this unit will perform properly from 208v-230v +- 10%, so there appears to be a quite wide range for voltage! like almost 60v, thankfully. Resistive loads will apparently output proportionately to the applied voltage, within the prescribed ranges.

Old man winter caused this one.

This property has a pool equipment room and outside shower which is remote from the house.

The Pool man came yesterday and turned on water to that equipment room and left.

Our sub zero winter froze a 1/2" cpvc hot water line in that remote location, though the water supply had been off for the winter. Unbeknownst to everyone, the hot water ran all night long, making the water heater seem as if it was not heating...when it was.

Sure enough the 18amp draw was right, watts were consumed! The leak was small enough and the flow moderate enough that at the heater there was no perceptible sound of water flowing. The sound at the heater was just the normal sound of the element being on.

We chased a similar ghost 25 years ago with a sneaky T&P valve leaking. In that case it was a similar slow leak, but still enough to cool the hot water. In that case the outlet for the t&p exited two floors below outside of another condo unit, so similarly we never saw the outflow until many hours later.

Thanks for all the tips! All contributions appreciated.
 
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