Originally Posted by Samflhomes
My heater is a an Atwood 10 gallon combo gas electric model 4e
What is the exact
model number from the rating plate inside the outside door? That will make a big difference.
From the pictures you've posted so far in this thread and your other other thread, it looks very much like my own Atwood GC10A-4E heater. The following is assuming that this is true, my statements may not be correct if you have a different model.
You measured 10.4 ohms on the electric element, so it is likely good. To be absolutely sure, you should take two more measurements: with the meter still in Ohms mode, and both wires disconnected from the heater, measure from each terminal of the heater to ground (the metal of the tank.) Both of them should read very high resistance (probably an "OL", "OV" or other error indication on the meter.) If so, the element is good. If either terminal reads low resistance to ground, the element is shorted to ground internally and will need to be replaced (this is unlikely.)
A big clue is that it is still working on gas. If you have the same model as I do, then you can rule out the thermostat, high limit switch, thermal fuse, and most of the control board. The same controls (thermostat, high lmiit, etc) operate both the the gas and electric side of the heater. So if gas is working, electric should also. The ECO is only used on the gas side.
With gas working, that leaves the electric control side:
For the following measurements, set your meter to measure DC volts using the DCV switch position, and the leads in the center and right sockets. Keep the black lead (from the center meter socket) on a good ground (clean exposed metal on the MH frame or water tank - like the body of the pressure relief valve.) Touch the red lead (from the right meter socket) to the points to be tested. Where I say 12V in the following steps, it's actually whatever your battery voltage happens to be which could be anywhere from a little below 12V to over 13V. Any reading like that is good.
The inside control switch should be 12V, and should provide 12V on the white wire going to the control board: 12V when the switch is on, nothing when the switch is off. If you don't get anything in either switch position, the switch is bad or there is a blown fuse or broken wire somewhere in the path between the battery and the water heater. I can't give you specific advice since the details depend heavily on the coach's make, model, and year, and I have no experience with your coach.
If that is working so far, the yellow wire coming from the control board controls the relay on the back of the water heater. If the control switch is on, and the water is cold, there should be 12V on that wire. If the control switch is off, or the water is already hot, there should be no voltage on the yellow wire. If either of these statements is false, there is a problem on the control board, or a bad connection where these wires attach to the control board.
Next, check the voltage at the back of the water heater. First, turn OFF the circuit breaker for the water heater, we don't want any high voltage back there while making these measurements!
With 12V present on the yellow wire (from the previous step) measure the relay contact that has the yellow wire. It should also be 12V. If not, there is a break or bad connection in the yellow wire. Now, check the other low voltage wire terminal of the relay, this is the wire (black?) that goes to the ground screw on the back of the heater, not the wires that go to the element or power cord. That should not read any significant voltage: if it does, that wire is broken or has a bad connection.
As a final test, while you are looking at the relay, have someone flip the electric control switch on and off, you should be able to hear some soft clicking from the relay as it switches. Now, with the AC breaker still off,
and the meter set to measure resistance again, measure the resistance of the two relay terminals where the high voltage wires to the element and power cord attach. With the control switch off, they should read high resistance. With the control switch on and the water cold, they should read very low resistance. If they always read high resistance, the relay contacts are bad and the relay must be replaced.
If all is good so far, the low voltage controls are good, and it's time to work on the high voltage side. Turn on the AC breaker to the water heater, set the meter to ACV, and be very careful! There are now dangerous voltages present at the back of the water heater, do not accidentally touch or short any exposed wires!
There should be a black and a white wire coming in to the relay box from the power cord. Black goes to the relay, white to the heating element. Measure across these two terminals, and you should see about 120 volts. If so, you have a break in the wires somewhere in this relay box. The circuit is quite simple: power comes in on the black lead, goes through the relay contacts (already determined good in the previous step) then through the heating element, and out the white wire. With everything connected up, and 120V coming in the black and white wires, there should be 120V on the heating element when the control switch is on and the water is cold, and no voltage on the heating element while the control switch is off or the water is hot.
If you aren't getting 120V on the white/black wires of the incoming power cord, then the problem is in the coach wiring. Your water heater might be hard-wired into the coach, or it might have a cord with a regular three prong plug plugged into a regular AC outlet behind the water heater. From there, it may go through any number of junction boxes as it works its way back to the breaker panel. If you open up the cover of the breaker panel (be very careful, there is high voltage and high current in there with lots of exposed wiring points!) you should be able to measure 120V between the output screw of the breaker and the bus bar where all of the white wires connect. If not, you have a bad breaker.
If you do have power on the output screw of the breaker, but not coming in the power cord at the back of the heater, then you have a break in the circuit somewhere between the two. I can't offer any specific advice there because the way the wires are routed and connected vary widely between different makes, models, and years of coaches.
You mention you have a Progressive EMS. As long as you have ANYTHING in the coach that is working properly on AC power (like the air conditioners, but not including things on an inverter) then the problem is likely not there. If you have power on the output screw of the water heater's circuit breaker, it is definitely not a problem with the EMS.
However, there are two types of EMS systems. Many coaches have a load shedding EMS that will turn off certain non-critical circuits if too much power is being used from the shore cord. On my coach, I also have an Intellitec EMS built into the breaker panel, and one of the loads that can be shed is the water heater. Do you have a system such as that? If so, what is the exact make and model number? Can you verify that it is not trying to shed the AC power to the water heater?