Melted Atwood 10-Gallon Water Heater Relay Harness

[JoelP]

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.

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.

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.

In my RV there are two "breaker"/service panels. One is for the 120V circuits and the other is for the 12V circuits. When I say that I am troubled that the breaker didn't trip I am referring to the little pop-out breakers for the 12V circuits. It seems to me that should have popped out before a wire would melt. It was the 12V side of the relay where the harness melted. I plan to pull that 12V service panel and have a look at this to see if there is something obvious that could have caused this. This won't happen soon since I would need to take my RV back out of storage, level it and then open the bedroom slide to get to this.

 

[bigbAZ]

In my RV there are two "breaker"/service panels. One is for the 120V circuits and the other is for the 12V circuits. When I say that I am troubled that the breaker didn't trip I am referring to the little pop-out breakers for the 12V circuits. It seems to me that should have popped out before a wire would melt. It was the 12V side of the relay where the harness melted. I plan to pull that 12V service panel and have a look at this to see if there is something obvious that could have caused this. This won't happen soon since I would need to take my RV back out of storage, level it and then open the bedroom slide to get to this.

My Winnie, and I believe most motorhomes, also has 12 volt breakers, but they are for major things, see pics below. Then it also has a 12 volt section in the load center with fuses (see 2nd pic below), which is supplied from one of the bigger 12 volt circuit breakers in the first pic below. Your 12 volt water heater relay circuit is likely protected by a fuse from the load center, not one of the bigger 12 volt circuit breakers. I could be wrong but I'd bet a beer I'm not.

 

[Kirk]

I am referring to the little pop-out breakers for the 12V circuits.

Your 12 volt water heater relay is likely protected by a fuse from the load center, not one of the bigger 12 volt circuit breakers. I could be wrong, but I'd bet a beer I'm not.

I would be amazed if bigAZ is not correct. I sure would like to see the replaced parts and have a conversation with the tech who repaired your water heater.

 

[gwinger]

In my RV there are two "breaker"/service panels. One is for the 120V circuits and the other is for the 12V circuits. When I say that I am troubled that the breaker didn't trip I am referring to the little pop-out breakers for the 12V circuits. It seems to me that should have popped out before a wire would melt. It was the 12V side of the relay where the harness melted. I plan to pull that 12V service panel and have a look at this to see if there is something obvious that could have caused this. This won't happen soon since I would need to take my RV back out of storage, level it and then open the bedroom slide to get to this.

The burnt insulation is not because of over current. The heat is produced because the wires probably came loose. Not much different that the 'stab on' receptacles or the cheap plastic power strips. They don't trip the breaker but do melt down.

 

[CharlesinGA]

Complete wiring diagrams for a 2010 Suncruiser 37F

The Atwood relay is small and has regular 1/4 inch spade connections for both the 12v control and the 120v connections. I'll bet the connections became loose or corroded and heated up. They make high temp, high pressure spade connectors and that is what should be used on the 120v connections on the relay.

That it cooked is really not much more than ordinary expected mechanic failure for a 16 year old RV.

The water heater gets its 120v power from a Load Shed Control Module (one of two in the coach).

Too may things don't make sense. He talks about a heat exchanger connected to water heater.

Yes, it has a motoraid system that runs hot engine coolant thru a heat exchanger in the water heater tank. My View had a 6 gal motoraid water heater, but was not hooked up. I think WBO bought all motoraid type water heaters no matter whether they had the option to hook them up or not.

Indeed the 12v DC is controlled by a single fuse and that powers the gas and elect switches that power the circuit board, ignition,gas solenoid, and the relay for the heating element.

 

[Gary RV_Wizard]

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 unknown here is why & how did the relay wiring fail. "Melt" says it got excessively hot, but that doesn't necessarily mean high amp flow. As has been mentioned, a loose wire can cause arcing that will generate heat, and so will corrosion between wire & relay. And assuming the relay is question is the one that switches 120v power to the heater element, that relay is handling both 12v power and 120v power. Either one could cause a problem. So the relay and associated wiring can get hot without tripping a breaker.

• The contacts within the relay itself can get hot as a result of poor contact. Those contacts are carrying 120v power to the heater element, usually about 12A.
• The 12v electro-magnet that closes the relay contacts could fail (but that would likely trip the 12v breaker)
• The 12v wiring that energizes the relay (the primary wire) could have a loose or corroded connection to the relay primary terminals. They can get hot without exceeding the 12v breaker rating.
• The 120v wiring to the relay (the secondary wire) could have a loose or corroded connection to the relay secondary terminals. They can get hot without exceeding the 120v breaker rating.

 

[Kirk]

JoelP has not been back since 3 yesterday, but the fact is that with the limited information we have, none of us can say for sure what happened. There is not enough information to do more than guess, no matter how experienced any of us may be. Since Joel is satisfied with the service that he received, all of us should probably stop speculating. We may have opinions, but they do nothing to help Joel.

 

[JoelP]

I appreciate all of these replies. Thanks, Charles, for reminding me of the link to the circuit diagrams which I plan to study further. I had not thought about it being fused elsewhere, I plan to investigate that but expect that you are very likely correct. All that said, if there were a loose or corroded connection as Gary RV Wizard said, and it had a localized voltage drop, that would cause it to heat up. I am hard pressed to understand why that circuit wasn't drawing excess current that should have taken out a fuse. Isn't that the reason that circuits have fuses? Lacking the parts I may never know for sure, but I think that everyone had spent enough time on this issue to close this out. As Kirk says we are now just guessing for lack of enough data.

 

[Gary RV_Wizard]

I am hard pressed to understand why that circuit wasn't drawing excess current that should have taken out a fuse. Isn't that the reason that circuits have fuses?

Heat in an electrical circuit is caused by current (amps) struggling to get through resistance (ohms) somewhere in the circuit. If the resistance is low, it takes a high rate of amps to generate much heat and that rate may be high enough to trip a breaker or fuse. But if the resistance is much higher than expected, then heat is generated even though the amps remain relatively low (within normal range). Thus there may be high heat without excessive current flow. That's how electric heating works - a high resistance element is placed in the circuit, creating heat without tripping the breaker of fuse.

We don't know if that happened in your scenario or not, but it is a fairly common occurrence.

 

[Kirk]

Without having seen the replaced parts, we don't know if just a small area at some connection was hot or the entire wire harness. Experienced technicians can draw some pretty good conclusions from what the damaged parts look like. A bad connection with normal current usually heats a relatively small area while excessive current can melt the insulation along an entire wire. The other reason for my returning all replaced parts to the customer was that by so dong he at least knew that I did replace what I said that I did and anyone can see heat damage or burned areas, even without any knowledge of the equipment.