Checking a water heater element.

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Rene T

Rene T

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My friend just picked up a used 5vr. It looks like the heating element is not working. In fact the seller didn't even know it had the electric option. He always just used propane.
I want to check the element before I pull it out. I know I have to check the ohms resistance. What sort of numbers should I be looking for?  This is all new to me.  Do I need to drain the tank prior to checking? I don't want to remove it only to find it good then I'd probably have an issue getting the old gasket to seal if I put it back in.
 
It should read about 10 ohms Rene. Make sure the wiring is disconnected before reading across the terminals, and be sure the power is off before removing the wiring. You should not have to drain the tank. You can also read each terminal to ground. The meter should read "OL" doing that test.
 
X2, assuming that the element is rater at 1500 watts. Actually, if the element is dead, it will be open. Almost anything below around 50 ohms will provide some heating.

Joel
 
Don't drain before checking the element. If it is OK, it will burn up quick without the water in the tank. If it has an anode rod that should also be checked and probably replaced as well.
 
If you are familiar with using an ohmeter, here is the procedure...
1.  Make SURE the breaker is turned off that feeds the water heater.
2.  Pit the meter on the AC voltage setting and confirm absence of voltage.
3.  Remove one of the wires from the heating element and push it aside.
4.  Set your meter to the ohms scale and make sure it reads zero when you touch the less together.
5.  Put the leads on the two screw terminals of the heater element and see what it reads.
6  A 1500 Watt element should read approx. 12.5 ohms.  Don't sweat it if it's several tenths off.
7.  Put one lead on either of the screw terminals and the other to the metal case of the heater.  This reading should be a very high ohm value....probably in the mega-ohm range.
 
I have a spare element I picked up used a couple of years ago. I checked that one and it read about 9.7. I hooked up some wires to it, stuck it in a glass of water, plugged it in and within 4 seconds, water was boiling off the side of it. So I know that one is good because it heats up but the ohms reading is 9.7.
I'm going to check my friends tomorrow.
 
Rene, the last one I worked on was many years ago on a friends 5r, we found the problem was the thermostat on the wall above the heater.  We had to replace it.

Ed
 
Hfx_Cdn said:
Rene, the last one I worked on was many years ago on a friends 5r, we found the problem was the thermostat on the wall above the heater.  We had to replace it.

Ed
Click to expand...

Thanks Ed.
 
I'm not familiar with RV water heaters enough to know if they make a 1200W element, but one rated at 1200Watts would show about 10 ohms.....so it may be that!.
 
Some heaters have two circuit switches. One is on the wall inside and the other is on the heater outside on the heater unit mounted towards the bottom, somewhat hidden, It is a rocker type of on/off switch to disable the electric heating element, mainly used during winterizing I believe so if the heater is accidentally turned on without water, the element won't be fried.
 
regval said:
Some heaters have two circuit switches. One is on the wall inside and the other is on the heater outside on the heater unit mounted towards the bottom, somewhat hidden, It is a rocker type of on/off switch to disable the electric heating element, mainly used during winterizing I believe so if the heater is accidentally turned on without water, the element won't be fried.
Click to expand...

I am aware of that hidden switch. Suburban water heaters have that switch.  It was off when he 1st purchased the RV. I turned it on and we are now monitoring the heater.
 
Turning the switch on did not help.
I did check the element with a meter today and it appears good. The next thing to do is check the thermostat and the switch. When  operate that rocker switch, it just doesn't feel right. It feels like the internals are junk.
I think he's going to wait till next year to investigate further. I just gave one member all those parts from another heater. Oh well. Have to keep my eyes open for another junk heater.

And yes, the breaker is on. I shut it off then back on.
 
With the heater cold, and the switch on, is there 120 volts across the two heater element? If not, with the rocker switch on, is there 120 from each terminal of the rocker switch to ground or neutral? (neutral is better to check to, that makes sure the neutral is good.)
 
kdbgoat said:
With the heater cold, and the switch on, is there 120 volts across the two heater element? If not, with the rocker switch on, is there 120 from each terminal of the rocker switch to ground or neutral? (neutral is better to check to, that makes sure the neutral is good.)
Click to expand...

No there isn't 120 volts across the element. Can't get to the backside of the switch. I started to try and pop it out to get to the backside but it was very brittle and started falling apart so I just left it for now. Will investigate further next year. He's leaving to go home in a couple of days. In the meantime, it's running off propane. .
 
Rene, if he isn't getting 120 across the element, and you are getting a resistance, then it is in the power to or from the element.  You could try hot wiring across one switch at a time to check, and if that isn't it, try hot wiring the element to see if maybe there is a break in the wires.  My gut says it is the switch that is crumbling.

Ed
 
Hfx_Cdn said:
Rene, if he isn't getting 120 across the element, and you are getting a resistance, then it is in the power to or from the element.  You could try hot wiring across one switch at a time to check, and if that isn't it, try hot wiring the element to see if maybe there is a break in the wires.  My gut says it is the switch that is crumbling.

Ed
Click to expand...

Ya Ed. Thanks. We'll see next fall. 
When you say "try hot wiring across one switch at a time to check" I think you're referring to the 2 thermostats. One must be a high temp thermostat (to shut off the power once temp is achieved) and the other must be the low temp thermostat (to turn on the power once the temp gets low).
 
I agree with Ed. I think he was saying hot wire across the rocker switch to see if you get power to the element, not across the t-stats. If the switch is crumbling, you may want to take it out anyway and tape up the wires so they don't fall off the switch and short or ground out. That happening could cause the breaker to trip if you're lucky, or even cause a fire if you aren't.
 
Mine quit working on the electric side.  Turned out to be that little rocker switch. Replaced it and all is good. Just pop it out and check the continunity.
 
Rene T said:
One must be a high temp thermostat (to shut off the power once temp is achieved) and the other must be the low temp thermostat (to turn on the power once the temp gets low).
Click to expand...


They?re both high limit thermostats, one for 12v and one for 120v. I was having all kinds of intermittent electric heating issues with mine when I bought it and ended up replacing the exterior switch, both thermostats and the element (along with the anode) and it?s worked perfectly since.
 

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Sun2Retire said:
They?re both high limit thermostats, one for 12v and one for 120v. I was having all kinds of intermittent electric heating issues with mine when I bought it and ended up replacing the exterior switch, both thermostats and the element (along with the anode) and it?s worked perfectly since.
Click to expand...

I know one assembly is for 110 volt AC and the other assembly is for 12 volt DC. I was wondering why there are 2 nickel size devices on each thermostat assembly. Is one of the devices a backup if one should fail
 
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