Holding Tank Sensor ID

Good Evening everyone -

While cruising for twelve days the past couple of weeks we had our holding monitoring system show both Low and Full at the same time and all filling of the holding tank stopped until we got a pump out. The books that came with the boat are the Dometic Sealand Tankwatch 4 system but as the photo attached shows there are three sensor leads hooked up to the Tankwatch 4 monitor display. Can someone assist in identifying this system and possibly a manual for cleaning the probes. Thanks, Bob

Your read out panel may be for a TankWatch 4, but, based on your photo, that's not what you have. This is what TW 4 sensors look like.

https://www.defender.com/product.jsp?id=105333

If I were you I'd replace the whole thing with a SCAD Tank Monitor...top rated, reasonably priced (available from a number of retailers including Amazon), the sensors go on the outside of the tank, so can never become clogged as internal sensor do. The TW 4 wiring--at least the ORIGINAL wiring (who knows what you have now)--should work with it. Scad Tank Monitors


--Peggie

Sensors

Peggie -

Thanks for the response. There appears to be only one of the sensors that is not working - so I am going to try to fix it. I can get the rod up but not out. Does someone know how to take entire rod out because it is most likely the end that is fouled. See photos.

Bob

Holding Tank Sensors

Hi everyone -

Update - the ol' flat bar works great to take the rubber grommets out of the tank for inspection of the probes. The probes were not bad at all once you got passed the stench. No real scale on floats and they cleaned up just with a shower from the hose.

However, when I tested them out and in a clean bucket of water it is very confusing. The red "Full" light works well - when float goes up it comes on. But the yellow "Low" level light remains on all the time - even when red "Full" light is on. When all floats are out of bucket and down on rod - no green light for "Empty". The "Mid" level light never comes on regardless of float position. Maybe I need to trouble shoot Monitor board itself or carefully look for a broken wire via some continuity checks. Any thoughts or have others had the same problem?

Bob

It looks like all three sensor wires go to the one connector. I would clean and check that connection point. But I am guessing and simple to do.

Gonna need to jump a few wires or if you have a power probe to test the circuts going to the controller. Since swapping out floats involve some wire work. Maybe a float is shorted out inside. Have you checked continuity for all 3 floats if they are opening and closing first? That looks simple without cutting wires. Those destuch connectors are nice and easy to pull wires out of the harness to. Oh does the light go out as well when you uplug the harness? May have a short also between harmess to controller.

Success

Update -

It has been a good week for our sanitation system repairs. Not a pleasant week from a smell standpoint but it is always nice to get it right the first time.

The bellows on our guest head failed and put some pretty unsavory stuff in our bilge. The folks that support Dometic / Sealand products at Aqua Star were a great help. They immediately knew that I needed a new bellows and two O-rings to fix the vacuum generator so on with the gloves and in a scale scraping day; I got the generator cleaned up with a new bellows, 2 O-rings, and 4 duck bill valves we were back in business and holding a good vacuum.

I then talked to them about the holding tank leveling system in our boat and sent them the photos above. They recommended a continuity check on the probes and that is what I did. It was difficult getting my multi-meter probes onto the correct pins in the Deutsch connector but I was patient and checked my readings about four times. Basically out of the three probes only the full probe read properly - the Mid and Lower/ Empty probes had no connectivity.
So I got the entire set from Aqua Star and put them in this afternoon - all the lights function as they are supposed to when I tested them before entering the tank - a functioning Tank Watch 4 system. BTW Aqua Star told me how to pry up the grommets with a flat bar and not to use grease on the rubber stopper that goes into the grommet but use soapy water - It worked great. A good day on the boat and all odors are gone. Photos of vacuum generator and new probes received today are attached.

Bob

Cheers. The floats easiest part to test!