Heating element where is the heating element on a atwwod heater?

heating elements are resistors that get hot
one end will have 115 volts but the other end should be considerable less because the resistance of the heating element drops the voltage
if you used a ohm meter you should be reading a resistance of 500-1000 ohms for a good heater element but with your readings , there will be no resistance so the element is faulty

Th easy fix would be installing a new heating element that has burned out. You don't say what size this tankless heater but if it stopped working entirely you might have just one heating element inside. You can test it by (1) turning off the circuit serving the heater, disconnecting one of the wires to the heating element, then taking an ohmmeter to see what the resistance of the element is. If it is "infinity" then it is open and burned out. Replace element. If it is around 6 ohms (for a 10kW heater running at 240V) then the heating element is OK. Unfortunately those heating elements don't last forever. Check the repair manual on how to replace the heating element.

Replace heating elements can be found at amazon, click here and take a look: Amazon com rheem heating element . I hope this was helpful... cheers

1) Copy following link for 3-step testing water heater elements.
http://waterheatertimer.org/How-to-test-water-heater-element.html

2) You need $10-15 multimeter from local hardware

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

See item # 9 ( 93844 ) at this link. Most RV places should stock the valve.
http://www.atwoodmobile.com/manuals/waterheaters/MPD%2093050%20PS%204.9.09.pdf

"BEWARE OF ELECTRICAL SHOCK HAZARD"!! Wires coming from a drain plug would indicate to me that someone has used a "hot rod" type element in the water heater. They are an aftermarket heating element, that would be plugged in somewhere, (usually inside to a receptacle) that would supply 120 VAC (hydro) to it. BE REAL CAREFUL THAT THOSE WIRES AREN'T LIVE.!! Go in trailer and access rear of water heater if that's where the wires appear to be going and make sure it's not plugged in somewhere. When you removed it, was it similar to a round rod , or just a plug?

Try taking that little thermo cut-off out of the circuit. It's inside the plastic sleeve. Look close where it attaches, remove it, and connect wire to where it was connected and then try it. Also make sure electrode is clean and aligned to sense the flame from burner. Let me know.

I do not know what heat control valve you are referring to on an electric water heater. On an electric water heater it has two heating elements in most cases. One at the top and one on the bottom. One of these is more than likely defective. Turn the power to the water heater off at the service panel or at a disconnect switch. Now take the covers off both heating elements. Check each one with a ohm meter to see if you have continuity. If your meter reads nothing that heating element is bad and needs replacing. On each heating element is a thermostat to set the temperature. Set the upper element to 120 degrees and the lower element to 130 degrees.

The heating element was bad. It's hard to believe that a brand new water heater would have a burn element, but that's the problem. I replace the heating element and its started working properly.

THE LIGHTED SWITCH SHOULD BE THE 12V ENERGY SOURCE TO ACTIVATE THE LP SIDE OF THE HEATER. THERE SHOULDN'T BE A LIGHTED SWITCH FOR THE 110 SIDE. THERE SHOULD BE A SWITCH OR A COMBINATION OF SWITCHES. ONE ON THE WALL LIKE A LIGHT SWITCH AND ONE MOUNTED BEHIND THE HEATER.