Water sensor issue (2 Viewers)

[felix1047]

Hi, I have a Hymer B614. I'm having a problem trying to remove a faulty Water sensor unit from the fresh water tank and would appreciate any advice on how this can be done.

 

[Tootles]

Do you have any pics? Is the type that enters through the side of a polypropylene tank, or is it fitted within the top cap?

 

[JeanLuc]

You need to access the top of the tank which will be located in the double floor. The sensor used by Hymer is normally a rod-type Schaudt unit that has a round top and is fitted through hole in the tank. It is held in place by a screw collar that you unscrew from inside, gaining access via the main tank screw hatch (about 6 inches in diameter). Here is the sensor unit.

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[felix1047]

Thanks for the information, will give that a go.

 

[JeanLuc]

Another thought - before changing the sensor, make sure it is not contaminated. If, for example, you have used a lot of hard water, there may be lime-scale on the rods and this could affect it's operation. I would try rubbing the rods gently with a green scouring pad to clean them well and then test the unit again. Also you need to be sure that the problem is the sensor and not the control panel.
As an aside, dirt can also affect the sensor in the waste tank. Periodically, I remove the cleaning hatch on the waste tank, flush it out well and clean the sensor rods with a scouring pad.

Another thing to note when asking for advice, it's worth stating the make model and year of your motorhome. By this I mean the model year, not the year it was registered as dealers can hold stock for some time. This can help the relevance of responses as systems can change between model series of course.

 

[DanielFord]

They never work properly, even a new one is going to give random readings after a few weeks. Clean the tanks and see if that helps.

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[felix1047]

Thanks again for the information. The probes on the unit are clean.Can you run a meter across the probes to check for functionality? How do you check whether the control panel is at fault?

 

[JeanLuc]

Thanks again for the information. The probes on the unit are clean.Can you run a meter across the probes to check for functionality? How do you check whether the control panel is at fault?

Sorry, I don't know whether you can test the sensor with a meter and I'm not sure how to test the control panel. It may depend on which panel you have. Mine from 2003 for example has two meters with needles to display values; later models have LCD panels. With needle meters, it's easier to see if one of the meters is not working properly.
If you want advice on how to test both items, I suggest an email to Udo Lang at Schaudt to ask him but be sure to include the model number of the control panel (normally printed on the front) and describe any symptoms fully. Udo.Lang@schaudt-gmbh.de

 

[tonyidle]

If it's a rod type sensor it is electrically just as it looks. It has 5 rods: one common (the longest) and 4 cut to different heights to represent the levels marked on the meter. Shorting any rod to the common one should cause the meter to move to the appropriate position. The sensor can give accurate readings but if it doesn't, and the wiring is OK, the only possible faults will be one or both of the following: A disconnection between a rod and its wire will give no reading at all for the level that that rod represents. A poor connection between a rod and its wire (variable faults depending on whether its the common rod or one or more of the others).

In the case of my own the faults were both the ones mentioned and were intermittent. The cause? I found that each rod could be pulled out of its hole in the top plastic holder. The holes were lined with a split copper tube soldered to a wire and all the copper tubes were green. The rods and copper connectors are embedded in hard resin that allows water into the copper/stainless steel connection hence the verdigris and intermittent connections. I believe that sooner rather than later all sensors of the same type will fail for the same reason and thus develop a reputation for unreliability. Renewal will still mean the new sensor is prone to the same fault.

I don't have a simple DiY permanent fix but what I did was to remove the rods, cut off the wiring and machine out the resin & copper on a lathe. I put a blob of braze (or bronze weld for the purists) on top of each rod, soldered the correct wire to each rod, replaced them in the cap, and filled the void with Sikaflex. So far so good and it has read accurately for 18 months since.

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[Cavs]

I have similar sensors on mine and went through the cleaning routine recently.

I tested the rods by removing the sensor, connecting it back to the control panel then shorting the rods to the common feed as @tonyidle suggests. However, I found that to test properly you have to short all the rods that would be in the water at a particular level. For example, shorting the common rod and the shortest one produced an error on the panel (Schaudt digital display). To test the 'full' position I had to connect all the sensing rods together, then short them across to the common.

One simple way to test a sensor would be to swap the wiring connectors and see whether the fault appears to be relocated to the other tank.

 

[tonyidle]

I have similar sensors on mine and went through the cleaning routine recently.

I tested the rods by removing the sensor, connecting it back to the control panel then shorting the rods to the common feed as @tonyidle suggests. However, I found that to test properly you have to short all the rods that would be in the water at a particular level. For example, shorting the common rod and the shortest one produced an error on the panel (Schaudt digital display). To test the 'full' position I had to connect all the sensing rods together, then short them across to the common.

I'd forgotten that bit until you mentioned it.

 

[felix1047]

Thanks to everyone for their input.The information has been very helpful to me

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