Melted Atwood 10-Gallon Water Heater Relay Harness

[JoelP]

Recently on a trip my electric hot water heater worked for one day and was not working the next. Fortunately, the propane heater was working just fine. I made the assumption that in a 16-year old RV the heater element was shot. Unlike the Suburban versions of this where the relay and element are easily accessed from the front, in the Atwood this is all at the back and requires removing the unit from the cabinet, disconnecting the gas and water lines, and electrical connections. To make it more complicated this unit has a heat exchanger that needed to be disconnected too, so I opted to take it to my neighborhood shop and have them do this.

Today when I got it back, I learned that the heating element was fine, but that the wire harness feeding the relay was melted. Apparently, the relay failed and took the harness with it without tripping the breaker. My question is how is that even possible? Why wouldn't the 12V breaker for that relay trip? Can I even trust those 12V breakers?

At first, I assumed that the relay had to be fine, since the propane heater worked, but that isn't the case. There seems to be a separate temperature control for propane activation.

I am very glad that I didn't try to fix this myself in that it involved draining the water heater, draining the coolant to the heat exchanger, removing the entire unit and then replacing the relay and wire harness. What a headache that would have been for me! Whiule I like to fix most things myself I was quick to realize that this was better done by someone else.

 

[gwinger]

Recently on a trip my electric hot water heater worked for one day and was not working the next. Fortunately, the propane heater was working just fine. I made the assumption that in a 16-year old RV the heater element was shot. Unlike the Suburban versions of this where the relay and element are easily accessed from the front, in the Atwood this is all at the back and requires removing the unit from the cabinet, disconnecting the gas and water lines, and electrical connections. To make it more complicated this unit has a heat exchanger that needed to be disconnected too, so I opted to take it to my neighborhood shop and have them do this.

Today when I got it back, I learned that the heating element was fine, but that the wire harness feeding the relay was melted. Apparently, the relay failed and took the harness with it without tripping the breaker. My question is how is that even possible? Why wouldn't the 12V breaker for that relay trip? Can I even trust those 12V breakers?

At first, I assumed that the relay had to be fine, since the propane heater worked, but that isn't the case. There seems to be a separate temperature control for propane activation.

I am very glad that I didn't try to fix this myself in that it involved draining the water heater, draining the coolant to the heat exchanger, removing the entire unit and then replacing the relay and wire harness. What a headache that would have been for me! Whiule I like to fix most things myself I was quick to realize that this was better done by someone else.

Chances are the connection on the relay or the breaker was loose. This will overheat the wire.

 

[John From Detroit]

Gwinger is correct a poor connection due to corrosion or a screw loose will do that.

Check all the screws in your breaker box too I had one that took over 3 turns and several that were loose when I did mine. a #2 Square screwdriver bit is a nice thing to have.

 

[bigbAZ]

Today when I got it back, I learned that the heating element was fine, but that the wire harness feeding the relay was melted. Apparently, the relay failed and took the harness with it without tripping the breaker. My question is how is that even possible? Why wouldn't the 12V breaker for that relay trip? Can I even trust those 12V breakers?

The breaker had no reason to trip if it wasn't overloaded. Wire terminations on both AC and DC get hot and burn up all the time, and even start fires without tripping a breaker. Did they show you the old parts? When they said it "took the harness out" chances are it was just the terminations and a bit of insulation near the terminations.

 

[gwinger]

The breaker had no reason to trip if it wasn't overloaded. Wire terminations on both AC and DC get hot and burn up all the time, and even start fires without tripping a breaker. Did they show you the old parts? When they said it "took the harness out" chances are it was just the terminations and a bit of insulation near the terminations.

Wires don't get hot for no reason. Either a high current draw, or mostly because the terminals are not tightened properly.
Another problem are those 'cheap' crimp on caps. If the wires aren't twisted tight before inserting them into the cap, they will loosen or pull out completely.
I know people will argue, but wire nuts are a much better alternative.
But, they are more expensive and take longer to install.
I've had at least two of those caps fail on my trailer. One was on the fan and light switch in the bathroom and one on the tail light.
I replaced the ones on all my tail lights with water proof wire nuts.
These are silicone filled.

 

[bigbAZ]

Wires don't get hot for no reason. Either a high current draw, or mostly because the terminals are not tightened properly.
Another problem are those 'cheap' crimp on caps. If the wires aren't twisted tight before inserting them into the cap, they will loosen or pull out completely.
I know people will argue, but wire nuts are a much better alternative.
But, they are more expensive and take longer to install.
I've had at least two of those caps fail on my trailer. One was on the fan and light switch in the bathroom and one on the tail light.
I replaced the ones on all my tail lights with water proof wire nuts.
These are silicone filled.
View attachment 2486374

No argument there

 

[Kirk]

The 12V wire being melted seems really strange to me. The heating element is powered by 120V alternating current that is controlled by a 12V relay which is supplied power from the circuit board when electric heat is called for.

 

[gwinger]

The 12V wire being melted seems really strange to me. The heating element is powered by 120V alternating current that is controlled by a 12V relay which is supplied power from the circuit board when electric heat is called for.

View attachment 2486390

Any wire whether 12 volts or 120 volts will get hot if the connection is compromised. It may even be an internal connection on the relay.
The relay coil may also have a diode across it. If that diode shorts or leaks, there will be excessive current to ground.
The diode is there to prevent spikes when the coil is de-energized. Instead of a mechanical switch, the relay is energized by an electronic component on the control board, that may be damaged by that spike.
It's called flyback spike and happens when the coil de-energizes.
Too many years in electronics!

 

[bigbAZ]

That's why I asked the OP if they showed him the old parts. For all we know it could have been the AC line side that got hot and melted everything.

 

[gwinger]

Too may things don't make sense. He talks about a heat exchanger connected to water heater. 12 volt breakers, separate temp control for the propane. The unit has a fixed temperature thermostat that controls both propane and electric operation.
Looking at your schematic, the 12 volt supply feeds both electric and propane operation from the same 12 volt source. No separate 12 volt "breaker"(?) for the relay.
I agree that they should have showed him the failed parts

 

[Kirk]

Any wire whether 12 volts or 120 volts will get hot if the connection is compromised. It may even be an internal connection on the relay.

After 40 years of electrical maintenance work, I am well aware of that fact. I also have many years of experience with RV water heaters and let's just say, I have never seen anything like that. The power to that relay is from the circuit board and the connections involved are soldered. A bad connection in a 12V circuit getting hot enough to cause the "relay to fail and take out the harness" is extremely improbable.

He talks about a heat exchanger connected to water heater.

He probably has a "motoraid" model which has a line from the engine coolant system that passes through an internal heat exchanger in the water heater tank. They aren't all that common, but we had one in our fulltime class A. The wife loved having hot water when we would stop for lunch on the road. Ours was an Atwood but Suburban makes them also.

 

[John From Detroit]

He probably has a "motoraid" model

He said "To make it more complicated this unit has a heat exchanger " so yes.

I do not recall if the 12 volt wires were soldered or not on mine
Not sure how the 120 volt ones were connected .

 

[JoelP]

The breaker had no reason to trip if it wasn't overloaded. Wire terminations on both AC and DC get hot and burn up all the time, and even start fires without tripping a breaker. Did they show you the old parts? When they said it "took the harness out" chances are it was just the terminations and a bit of insulation near the terminations.

They did not show me the parts and unfortunately, I did not ask to see them, but this shop has been reasonably competent and honest with me in the past.

 

[JoelP]

Wires don't get hot for no reason. Either a high current draw, or mostly because the terminals are not tightened properly.
Another problem are those 'cheap' crimp on caps. If the wires aren't twisted tight before inserting them into the cap, they will loosen or pull out completely.
I know people will argue, but wire nuts are a much better alternative.
But, they are more expensive and take longer to install.
I've had at least two of those caps fail on my trailer. One was on the fan and light switch in the bathroom and one on the tail light.
I replaced the ones on all my tail lights with water proof wire nuts.
These are silicone filled.
View attachment 2486374

These connections were inside of well-sealed enclosure, so moisture protection doesn't seem to be any issue. This is especially true where I store it and use it in California.

 

[JoelP]

No argument there

I assume these were crimp connections, but I plan to look at the breaker panel to see if something jumps out at me.

 

[JoelP]

The 12V wire being melted seems really strange to me. The heating element is powered by 120V alternating current that is controlled by a 12V relay which is supplied power from the circuit board when electric heat is called for.

View attachment 2486390

I was told that the 12volt relay that controls the 120V to the heat4er element failed. I assumed that a short to the coil in the relay was the root cause for drawing too much current on the 12V side of the relay that could cause this meltdown.

 

[JoelP]

Any wire whether 12 volts or 120 volts will get hot if the connection is compromised. It may even be an internal connection on the relay.
The relay coil may also have a diode across it. If that diode shorts or leaks, there will be excessive current to ground.
The diode is there to prevent spikes when the coil is de-energized. Instead of a mechanical switch, the relay is energized by an electronic component on the control board, that may be damaged by that spike.
It's called flyback spike and happens when the coil de-energizes.
Too many years in electronics!

View attachment 2486507

This makes a great deal of sense to me. A failed diode would short 12V to ground.

 

[JoelP]

Too may things don't make sense. He talks about a heat exchanger connected to water heater. 12 volt breakers, separate temp control for the propane. The unit has a fixed temperature thermostat that controls both propane and electric operation.
Looking at your schematic, the 12 volt supply feeds both electric and propane operation from the same 12 volt source. No separate 12 volt "breaker"(?) for the relay.
I agree that they should have showed him the failed parts

As I read the schematic the relay only controls the 120V to the electric heating element not the propane operation. There is a separate thermostat that controls the unit from overheating the water and that continued to work on the propane side of this unit. That seems to service both electric and propane. My 10gal Atwood also has a heat exchanger that circulate the coolant from the engine to the hot water tank to heat the water while running the engine. That is a complication that forces one to drain the engine coolant when servicing the unit.

Interestingly they also replaced the electrodes. These are the parts that spark the propane when the unit calls for the propane to be fired up. Those electrodes, per the schematic, are powered right out of the controller, not the relay. I never asked why but assume these electrodes either were compromised when the wire harness was melted or they thought that these fail often enough that they might as well change them as long as they had the unit out of the rig. Given that their shop rate is $220/hr I was not unhappy to pay $900 plus parts for this work. I could never have done this in under 4 hours myself.

 

[JoelP]

After 40 years of electrical maintenance work, I am well aware of that fact. I also have many years of experience with RV water heaters and let's just say, I have never seen anything like that. The power to that relay is from the circuit board and the connections involved are soldered. A bad connection in a 12V circuit getting hot enough to cause the "relay to fail and take out the harness" is extremely improbable.

He probably has a "motoraid" model which has a line from the engine coolant system that passes through an internal heat exchanger in the water heater tank. They aren't all that common, but we had one in our fulltime class A. The wife loved having hot water when we would stop for lunch on the road. Ours was an Atwood but Suburban makes them also.

I would agree that connections to the controller are soldered. I have never had this serviced in the past 16 years so I doubt that the wires to the relay were reconnected, crimped or otherwise, but never having had this out to see the connections I cannot be sure. I feel that a dead short that can melt wires must trip a breaker and I am only trying to figure out why not. That is my biggest mystery.

 

[Kirk]

There is a separate thermostat that controls the unit from overheating the water and that continued to work on the propane side of this unit. That seems to service both electric and propane.

That is called the ECO and it has two thermostats, one to control the normal heating to the desired temperature and the second a safety device to prevent the temperature from running away if the first thermostat should fail closed. And you are also correct that in your water heater they control both modes of heating.

Those electrodes, per the schematic, are powered right out of the controller, not the relay.

The ignition probe does get power from the circuit board and it operates only when in the propane mode. It has no connection to the wires to the relay and should have absolutely no effect on it nor would it be affected by the 120V side.

I feel that a dead short that can melt wires must trip a breaker and I am only trying to figure out why not. That is my biggest mystery.

What melts the insulation of a wire is either extreme high current flow of heat from a poor connection and then only the part near that connection. A circuit breaker would have been involved only if the problem was on the 120V side. The explanation as you have given it bothers me that it doesn't match anything that I can think of for your water heater. But you mention that it has been 16 years without any prior service work so you may well be correct that some of what they did was just routine maintenance and that could be sound thinking, especially if the water heater has to be removed in order to do that work. It still bothers me that they didn't leave all of the replaced items for you to examine and/or destroy. In my career we always took all replaced items to the customer and showed him if he was interested. I insisted that any RV tech working on my RV do that too. It may well be that your people did do great work and they just don't do that and perhaps didn't explain what they did and why very well. What is important is that you are satisfied and that seems to be the case.