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Old 11-16-2021, 10:47 AM   #1
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Winnebago Trend holding tank heaters not working

We bought a 2015 Winnebago Trend 23B earlier this year and have absolutely loved it. I've pretty handy and have done several upgrades/modifications on it, including switching to Battle Born batteries, getting a large inverter, and adding a spare tire to the rear hitch.

However, I've come across a problem that I cannot solve and would like some help with. The holding tank heaters do not work, even when the temperature is in the low 30s F. When I turn on the holding tank heater switch, it lights up red. But no power goes to the holding tank heater pads. I've tested this with a multimeter. I've tested the fuse for the tank heaters, and it works. Interestingly, even when that fuse is pulled, the light on the tank heater switch remains on.

Does anyone have any information on what the problem might be and how I could resolve it? Thanks in advance!
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Old 11-16-2021, 11:22 AM   #2
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Are they Ultra Heat brand? On their web site they say the temp must drop below freezing but they don't say if that is a requirement for the thermostat to close or just a condition that should exist before you switch them on. You may have to get them a little colder. I have thought about testing mine with ice, or dry ice.
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Old 11-16-2021, 11:25 AM   #3
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Are they Ultra Heat brand? On their web site they say the temp must drop below freezing but they don't say if that is a requirement for the thermostat to close or just a condition that should exist before you switch them on. You may have to get them a little colder. I have thought about testing mine with ice, or dry ice.
The problem is that the tank heaters aren't getting any power. My understanding is that the heaters themselves have to get to around freezing to work, not anything in the RV. But perhaps there is a thermostat somewhere else that I'm not aware of.
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Old 11-16-2021, 11:35 AM   #4
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The problem is that the tank heaters aren't getting any power. My understanding is that the heaters themselves have to get below freezing, not anything in the RV.
I didn't catch that, My wiring just drops straight down the wall to the pads. How did you check, did you shove the meter leads into the butt connectors? When I get a chance I'll check mine but I do know that mine have the thermostats right in the heat pads. Is it possible yours has a thermostat before the pads?
I added a new elbow pad when I did my gray water mod and used sealing butt connectors with heat shrink but I can probably get some T pins in there to check. The elbow heaters don't have thermostats, just the tank pads. I don't want to find out they don't work when I am somewhere on the road, this is something I've been meaning to check and your post reminded me.
If yours are Ultra Heat you could email them, they are very helpful and responded to my email right away when I bought the elbow heater. Maybe they have a test procedure.
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Old 11-16-2021, 11:41 AM   #5
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They do have a test procedure which I am going to try. Meanwhile I think your issue might be another thermostat somewhere in the wiring or a broken wire, if you are positive you were getting good contact with your meter. https://www.ultraheat.com/faq (click on the basics then on dive in deeper)
It also says they should start working at 44F.
PS: Yours are 12 volt right? Some are 120 volt and could be operated by a 12 volt relay so the light would come on but no power to the pads if not plugged in. Just a guess.
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Old 11-16-2021, 11:44 AM   #6
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I didn't catch that, My wiring just drops straight down the wall to the pads. How did you check, did you shove the meter leads into the butt connectors? When I get a chance I'll check mine but I do know that mine have the thermostats right in the heat pads. Is it possible yours has a thermostat before the pads?
I added a new elbow pad when I did my gray water mod and used sealing butt connectors with heat shrink but I can probably get some T pins in there to check. The elbow heaters don't have thermostats, just the tank pads. I don't want to find out they don't work when I am somewhere on the road, this is something I've been meaning to check and your post reminded me.
If yours are Ultra Heat you could email them, they are very helpful and responded to my email right away when I bought the elbow heater. Maybe they have a test procedure.
Yes, I checked the voltage where the wiring split between two tank heater pads. I too added a new elbow pad to the drain assembly, but I know that it does have a thermostat in it. The wiring seems to go straight into the cabin, so I don't think that there is an exterior thermostat. It was 32 F when I tested it this morning, so that should be cold enough for the heater pads to turn on.
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Old 11-16-2021, 11:45 AM   #7
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They do have a test procedure which I am going to try. Meanwhile I think your issue might be another thermostat somewhere in the wiring or a broken wire, if you are positive you were getting good contact with your meter. https://www.ultraheat.com/faq (click on the basics then on dive in deeper)
It also says they should start working at 44F.
PS: Yours are 12 volt right? Some are 120 volt and could be operated by a 12 volt relay so the light would come on but no power to the pads if not plugged in. Just a guess.
I hadn't thought that there might be a broken wire somewhere. That would make sense, but it will also be difficult to find where it is if that's the problem.
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Old 11-16-2021, 11:47 AM   #8
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I hadn't thought that there might be a broken wire somewhere. That would make sense, but it will also be difficult to find where it is if that's the problem.
Just run a temporary 12 volt wire to them to see. If it's a broken ground wire it'll be easy to fix.
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Old 11-16-2021, 11:57 AM   #9
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Any experience with the heating pads we use for our sore muscles, etc?
I'm guessing there are a couple things at play here, one being that the pad will have some simple form of "thermostat" that is likely just a simple snap action bimetal that closes when cold and opens over that point.
They would want to control the temp at the actual point where it is important and that is the tank itself, not someplace inline like up in the body where it may not be at all the same temp.
Pipe heaters are built like this with a bulge in the line just before the heating element and that needs to be wrapped solid to the pipe to read correctly.
It could be as simple as this example and easy to miss spotting it:
https://www.newark.com/white-rodgers...rs-Transducers

If it was not done this way, you would have to be really alert and turn the heat on/off or you will be using power to heat the tanks when the temp gets to 50 during the day! One would not want to go to bed with the heaters running at 50 outside because it is going to drop to 20 in the morning!

The explanation for the light is easy also as it is common to use a different circuit for the indicator than the actual power to the heat. The heat takes large wires for the high current and it is much easier to use low voltage wires to tell you the switch is on.
We often get this in RV control items as they use lots of really small 12 volt led to indicate things are on---even when the 110 Ac breaker is tripped!
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Old 11-16-2021, 01:03 PM   #10
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Any experience with the heating pads we use for our sore muscles, etc?
I'm guessing there are a couple things at play here, one being that the pad will have some simple form of "thermostat" that is likely just a simple snap action bimetal that closes when cold and opens over that point.
They would want to control the temp at the actual point where it is important and that is the tank itself, not someplace inline like up in the body where it may not be at all the same temp.
Pipe heaters are built like this with a bulge in the line just before the heating element and that needs to be wrapped solid to the pipe to read correctly.
It could be as simple as this example and easy to miss spotting it:
https://www.newark.com/white-rodgers...rs-Transducers

If it was not done this way, you would have to be really alert and turn the heat on/off or you will be using power to heat the tanks when the temp gets to 50 during the day! One would not want to go to bed with the heaters running at 50 outside because it is going to drop to 20 in the morning!

The explanation for the light is easy also as it is common to use a different circuit for the indicator than the actual power to the heat. The heat takes large wires for the high current and it is much easier to use low voltage wires to tell you the switch is on.
We often get this in RV control items as they use lots of really small 12 volt led to indicate things are on---even when the 110 Ac breaker is tripped!
That makes sense.

So is it your suspicion as well that there's a broken wire somewhere?
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Old 11-16-2021, 01:19 PM   #11
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Just run a temporary 12 volt wire to them to see. If it's a broken ground wire it'll be easy to fix.
You mean run a temporary 12 volt wire to the tank heater pads to see if they work? That makes sense, but I don't see how that will help me locate where there's a line break, if there is one.
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Old 11-16-2021, 01:25 PM   #12
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You mean run a temporary 12 volt wire to the tank heater pads to see if they work? That makes sense, but I don't see how that will help me locate where there's a line break, if there is one.
It will show you which wire is bad then you can run a new one taking whatever route you can get to and abandon the original. But first, in light of the fact that the indicator lights up when the fuse is pulled, this means there might be a second circuit and maybe a relay. If so running a new wire from the switch won't be the answer. A call or email to Winnebago might get you a schematic. Also did you test from positive to the frame to see if maybe the ground is open? If the ground is open you can easily run a new one from the frame. Also make sure your fuses are labeled correctly and you are pulling the right one.
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Old 11-16-2021, 01:37 PM   #13
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That makes sense.

So is it your suspicion as well that there's a broken wire somewhere?
Depends on some other info but this would be my guess at what might be happening and it may not be a problem at all? Or you may know more about what happened and spot a flaw in my thinking!

What I suspect is that you are assuming the tanks to be colder than actual. With outside temps in the thirties and you are heating the inside, I'm guessing(?) the tanks will take a pretty long time to actually get down to whatever point they have chosen to have them heated to prevent freeze.

For example if they choose 35 to turn on ( That's what the pipe heaters I have used do) an outside temp of 20 will take a long time to get 15-20 gallon of fluid down to 35. Several things involved to change how long and if you are heating inside, how much of the heat is going to the tanks and how much is in the tank will change the time. A gallon bucket of water setting totally outside will not freeze overnight when it's 30 outside! It gets a skim of ice but not actually frozen in lots of cases as it has enough mass that it takes a while to get all the heat out to really freeze.

So does this fit what might have happened? Say you have a half full tank and you drop a couple quarts of 98.6 fluid in and go to bed? That half tank of fluid may be at near 50 when you go to bed and the warmth from the RV is possibly keeping it near 40 by morning!
The indicator light shows you have the system turned on but the little switch laying right on the plastic side of the tank never closes because the fluid is still warm?

I'm thinking the system is more complex and works better than us having to remember to turn it on and off as the temp outside varies but is more "automatic" in that we turn it on but it doesn't actually start working until the tank contents cool off enough to need the heat.

I admit to lots of guessing on that as we don't get the really good wiring info on post 2010 models that would let us look at wire by wire to see what's there.

This is kind of related to heat tapes for pipes and they do have lights to indicate they are powered. That was great when we had a pool with exposed pipes as I could see from the window that the tape was getting power but it did not actually turn on and heat until late as the temp actually reached freezing!

But as a way to avoid freezing your pipes, I might feel better if you could ask some of the folks who make the tank heaters as we never know FOR SURE they are taking care of us as well as hoped!

If we could look at the wires to the heaters and see an open circuit and then run the tank temp down below freezing and see it close, we could test but it hard to change the temp on something that big with what most of us have on hand.

I'm "thinking" you are good but just not getting the tank contents cold enough but I'm a long way from being the guy that has to deal with me being wrong!
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Old 11-16-2021, 01:38 PM   #14
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Out of curiosity I Googled 12 volt heat pad wiring schematics and none showed a relay, just a direct wire from the fuse to the switch to the pads and a ground. Then I went out and checked mine, it's on a 15 amp fuse. When I remove the fuse the switch no longer lights up. I know our rigs are different but they are also very similar and I can't see why the indicator light would be on a different circuit, if it is only a single pole switch that would require a relay. A relay is only needed when the load exceeds the switch rating.
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Old 11-16-2021, 01:40 PM   #15
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I'm "thinking" you are good but just not getting the tank contents cold enough but I'm a long way from being the guy that has to deal with me being wrong!
The problem with this theory is that he is not getting voltage at the pads. With the thermostats located in the pads there should be voltage at the pad pigtails ahead of the t-stats whenever the switch is on regardless of temperature.

If I had to guess I would say the ground is missing/open or the tester did not make good contact at the splice.
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Old 11-16-2021, 01:44 PM   #16
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That makes sense.

So is it your suspicion as well that there's a broken wire somewhere?
Depends on some other info but this would be my guess at what might be happening and it may not be a problem at all? Or you may know more about what happened and spot a flaw in my thinking!

What I suspect is that you are assuming the tanks to be colder than actual. With outside temps in the thirties and you are heating the inside, I'm guessing(?) the tanks will take a pretty long time to actually get down to whatever point they have chosen to have them heated to prevent freeze.

For example if they choose 35 to turn on ( That's what the pipe heaters I have used do) an outside temp of 20 will take a long time to get 15-20 gallon of fluid down to 35. Several things involved to change how long and if you are heating inside, how much of the heat is going to the tanks and how much is in the tank will change the time. A gallon bucket of water setting totally outside will not freeze overnight when it's 30 outside! It gets a skim of ice but not actually frozen in lots of cases as it has enough mass that it takes a while to get all the heat out to really freeze.

So does this fit what might have happened? Say you have a half full tank and you drop a couple quarts of 98.6 fluid in and go to bed? That half tank of fluid may be at near 50 when you go to bed and the warmth from the RV is possibly keeping it near 40 by morning!
The indicator light shows you have the system turned on but the little switch laying right on the plastic side of the tank never closes because the fluid is still warm?

I'm thinking the system is more complex and works better than us having to remember to turn it on and off as the temp outside varies but is more "automatic" in that we turn it on but it doesn't actually start working until the tank contents cool off enough to need the heat. Don't miss the point where it mentions a "sensor" as that may be what we are calling a "thermostat". You turn it on like your furnace but it doesn't actually heat until the "sensor/thermostat" calls for heat. This would look like an open wire on a meter.

I admit to lots of guessing on that as we don't get the really good wiring info on post 2010 models that would let us look at wire by wire to see what's there.

This is kind of related to heat tapes for pipes and they do have lights to indicate they are powered. That was great when we had a pool with exposed pipes as I could see from the window that the tape was getting power but it did not actually turn on and heat until late as the temp actually reached freezing!

But as a way to avoid freezing your pipes, I might feel better if you could ask some of the folks who make the tank heaters as we never know FOR SURE they are taking care of us as well as hoped!

If we could look at the wires to the heaters and see an open circuit and then run the tank temp down below freezing and see it close, we could test but it hard to change the temp on something that big with what most of us have on hand.

I'm "thinking" you are good but just not getting the tank contents cold enough but I'm a long way from being the guy that has to deal with me being wrong!
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Old 11-16-2021, 03:13 PM   #17
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Out of curiosity I Googled 12 volt heat pad wiring schematics and none showed a relay, just a direct wire from the fuse to the switch to the pads and a ground. Then I went out and checked mine, it's on a 15 amp fuse. When I remove the fuse the switch no longer lights up. I know our rigs are different but they are also very similar and I can't see why the indicator light would be on a different circuit, if it is only a single pole switch that would require a relay. A relay is only needed when the load exceeds the switch rating.
I ran a long wire directly from the batteries to the tank heater pad wiring, and as soon as I connected them, they started pulling current (60 watts for two of the three tank heater pads, as measured by my Victron Smart Shunt), so I know that the pads themselves are working. I've tested both the hot and neutral lines at the tank heater pads, and neither are connected to anything. The neutral line has no connection to the chassis frame or the neutral bus bar inside the coach, and the hot line has no connection to the fuse holder. So that must mean that somewhere there is a complete break in the line running from the tank heater pads to the fuse box. The lines are covered by a plastic wrapping, the kind you shove the wires into, and I cannot see any break between them and where the lines run into the coach. Pulling all the wire out of the wrapping to check the connections will be a cumbersome task.

I haven't checked yet whether the fuse marked as tank heater was marked correctly, but all the other fuses are marked and taken by other items, so I doubt that that's the source of the problem.

If I cannot find where the break in the line is, I suppose that I'll have to run a new line from the fuse box to the tank heater pads. That means that the existing switch won't work, but I could disconnect power to the tank heater pads when desired by just pulling the fuse.

Thoughts?
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Old 11-16-2021, 03:16 PM   #18
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Depends on some other info but this would be my guess at what might be happening and it may not be a problem at all? Or you may know more about what happened and spot a flaw in my thinking!

What I suspect is that you are assuming the tanks to be colder than actual. With outside temps in the thirties and you are heating the inside, I'm guessing(?) the tanks will take a pretty long time to actually get down to whatever point they have chosen to have them heated to prevent freeze.
As I noted above, when the tank heater pads are getting power, they are drawing power, so I know that the temperature being too warm isn't the problem. It's a wiring issue of some sort, but tracking it down may be very difficult.
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Old 11-16-2021, 05:03 PM   #19
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As I noted above, when the tank heater pads are getting power, they are drawing power, so I know that the temperature being too warm isn't the problem. It's a wiring issue of some sort, but tracking it down may be very difficult.
Sounds right and I would have to go with that as it is not easy to work on things without good info and we get very little on this one.

so if you have a set of wires with both positive battery and ground missing, my thoughts would jump to some plug loose and move to trying to get the info from Winnebago on location of a plug in the lines to the tanks.

Looking at many of the drawings on the pre 2010 models we can see that there are definitely drawings to show those locations and I see no reason there would not be that info on hand for their techs, so maybe a call to ask for that specific info would be a good move?
Maybe if one knew that plug was in a specific location like above a frig or under the couch, it would be as simple as replugging?

It could be as drastic as the wires caught on a sharp metal edge to cut them but when thinking of cutting both battery and ground at the same point and time, I think of tripping breakers! But if a plug is not snapped together well, I find that pretty easy to see falling apart!

It's a real guessing game when we don't have real info!
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Old 11-16-2021, 05:17 PM   #20
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Sounds right and I would have to go with that as it is not easy to work on things without good info and we get very little on this one.

so if you have a set of wires with both positive battery and ground missing, my thoughts would jump to some plug loose and move to trying to get the info from Winnebago on location of a plug in the lines to the tanks.

Looking at many of the drawings on the pre 2010 models we can see that there are definitely drawings to show those locations and I see no reason there would not be that info on hand for their techs, so maybe a call to ask for that specific info would be a good move?
Maybe if one knew that plug was in a specific location like above a frig or under the couch, it would be as simple as replugging?

It could be as drastic as the wires caught on a sharp metal edge to cut them but when thinking of cutting both battery and ground at the same point and time, I think of tripping breakers! But if a plug is not snapped together well, I find that pretty easy to see falling apart!

It's a real guessing game when we don't have real info!
That's a good suggestion. I'll try to call Winnebago tomorrow to see if they can give me some additional information. I don't want to run new wire to the tank heater pads if I don't have to.
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