Water Tank level shows full even if it is empty - Beneteau Oceanis 31

[Gigagybe]

Starting today my water tank level of my Beneteau Oceanis 31 shows full even if it is empty.
Could it be due to the module? Mine is the Scheiber module (mod 821195) in the picture where I unplugged the connector to spry CRC.
Do you know how could I troubleshoot easily before unmounting the tank?

Thanks & Fair Wind!

 

[jssailem]

What if you swap the leads as they connect to the display. Red for black. Could they be incorrectly connected? If swapped and they reverse the display, empty when empty, then possibly you solved the problem.

 

[Gigagybe]

What if you swap the leads as they connect to the display. Red for black. Could they be incorrectly connected? If swapped and they reverse the display, empty when empty, then possibly you solved the problem.

Thanks for your note. The shape of the connector does not let you swap so I don't think that's the issue...and it worked well so far.

 

[Ralph Johnstone]

Starting today my water tank level of my Beneteau Oceanis 31 shows full even if it is empty.

Have never dealt with the Scheiber module before. Do you know what the principle of the sensor in the tank is ?

Now this is the potable water tank and not the holding tank ?

Sitting in my armchair on the other side of the world, I can't help but wonder if it's the float principle and the float is hung up on the vertical rod at the top and always shows full.

If the sensor assembly is available on the top of the tank, it should be an easy job to pull it and check the float. If it's an SOB to get at the sensor, take the boat out and try to shake it up in rough water to free up the float.

If that doesn't work, the sensor would still be the first thing I would suspect as the cause of your problem.

 

[Davidasailor26]

I presume the level shows on a VDO panel, a bit like this?

If so the panel doesn’t work on the resistance principles like the float switches mentioned above. There are multiple sensors inside the tank. Depending on how high the fluid is a different number of sensors are covered. The sensor module you found converts the reading from those sensors to a voltage level (0-6V) that the panel reads. So, the possibilities are:
- Something has fouled the sensors in the tank and they read water all the time
- Something may have shorted in the sensor module and it’s always returning 6V.
- Something may have gone wrong in the VDO panel itself to make it think it’s getting 6V even when it’s not.

I’d probably start by checking the connections on that module. Maybe try disconnecting it to see if the panel drops to empty (or if the panel loses track of that tank entirely). That should help narrow the problem to something on the sending or receiving end.

 

[Leeward Rail]

Further to what @Davidasailor26 said...
I would contact the manufacturer of the sensor and ask their techs how the sensor works. Otherwise you are guessing on how to diagnose it.

I would do a quick visual inspection of the wiring from the sensor to the panel, if possible. If wire insulation has worn through at any place on the wiring, resulting in a short, it could cause false readings..

Do the obvious and easy faults first...

Corrosion and vibration cause a lot of problems with boat wiring.

• Check for clean, tight, connections (which you were obviously already doing since you were cleaning it with CRC contact cleaner).
• Visually inspect wires for damage.
• Pull the sensor from the tank to see if it is stuck, and then manually actuate the sensor and see if the level on the display changes.

Then figure out how the gauge functions and use that info to test the gauge and display seperately if possible, thereby isolating the problem.

 

[Leeward Rail]

If swapped and they reverse the display, empty when empty, then possibly you solved the problem

Bad idea.

If it is a typical resistance type gauge, polarity isn't a issue. Resistance is the same no matter which direction the current flows through a variable resistor.

It if isn't a resistance based level sensor....swapping wires without knowing their function, could fry the sensor if it has a logic board.

Fortunately any well designed component uses a connector that can only be connected one way. In addition, any connectors in the immediate area are usually intentionally different, to prevent mistakes.

 

[Gigagybe]

Hi All,
first of all thanks to all for your precious suggestions and help.

Luckily this weekend the gauge started to work again, not sure if this is because of the crc, the several plug/unplug, or.....simply because this was a beautiful weekend with sun and fair wind

I have not been able to open the inspection cap of the tank, it was really tight and I didn't want to damage it not having a safe place where to buy a spare part. Probably I would need to build a special tool to place in the cross of it.

In the meantime I also recovered the instruction module of the electronic module, I attach the link here in case someone else need it (it comes directly from the producer website):

https://www.scheiber.com/_files/ugd/084c74_1d23e41078de433fa2a5399e1e482f60.pdf?lang=en

Thanks again and fair wind!

 

[Ralph Johnstone]

I have not been able to open the inspection cap of the tank, it was really tight and I didn't want to damage it

Try warming the inspection cap with a hair dryer and it might come off as it expands. Monitor the temperature of the cap with your fingers until it gets good and warm and then twist with your hands only, no tools.

 

[justsomeguy]

I have not been able to open the inspection cap of the tank

Knowing the type of level sensor would be a good thing.
I have a "doughnut" float around the shaft of the sensor and if I have a boisterous sail, the sediment in the tank can make the float stick.

 

[Davidasailor26]

I have not been able to open the inspection cap of the tank, it was really tight and I didn't want to damage it not having a safe place where to buy a spare part. Probably I would need to build a special tool to place in the cross of it.

If I remember correctly @kodiak1120 built himself a tool to fit into the inspect port handle and help open it.

 

[kodiak1120]

If I remember correctly @kodiak1120 built himself a tool to fit into the inspect port handle and help open it.

Yes I did... unfortunately, I don't have the dimensions. But just basically cut the cross piece out of plywood and epoxy/screw it on to a longer piece of plywood. Works great.