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Fresh Water Tank keeps Leaking from Overflow Pipe


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....It is very likely that your fresh water tank has a full, and a "travel" setting on the drain valve.


The travel setting allows only a partial fill, usually around 20 litres, and if filled beyond this point the excess will then drain.


The nature of the working may vary, but on Hymer group vehicles like the Carado, if it uses a handwheel arrangement to close the valve, it requires another couple of turns or so to take it past the resistance felt at the travel position, such that it is then fully closed.


From a fully opened valve, closing it will hit initial resistance at the travel position that feels like it is closed. You need to continue to turn through that resistance (possibly a couple of extra turns) when it will free-up again, and then hit further resistance when it is fully closed.


You need to do this carefully, as it is not unknown (but rare) for the system to break if forced. You may be able to test the theory by fully opening the valve, and, if it was fully closed, you will probably feel it go past the travel position at two or three turns. If you don't feel such increased resistance at a couple of turns on opening, it was probably only closed to the travel position.


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sounds like the 20% valve is working, if you have a fresh water hand wheel type valve, normally red in colour. when you close it it has two stops, a soft stop which allows you to retain 20% of the tanks water or a full hard stop which allows you to fill the tank to 100%. The 20% is to afford you less weight when travelling but enough water to do minimal thinks like make a cup of tea and flush the loo LOL, think the boiler is separate but I am sure someone will correct me if I am wrong.

The red hand wheel is normally positioned in or near the fresh water tank.

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Same arrangement as my T339 by the look of it. As previously stated, most likely that the drain valve isn't fully closed & requires a couple of turns more beyond the "travel limit" drain setting soft stop - try turning the valve beyond the point that it goes stiff & it should go free again before stopping at the fully closed position.


Nice to be able to drain the water tank from inside the van on Carados rather than grovelling about under my previous Chausson to remove a push-on stop end from the drain tube.


Nigel B


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Our Hymer fresh water tank has exactly this arrangement. It does sound like your valve could be stuck at the 20 litre mark.


The triangular wheel connects via the shaft to the valve at the bottom. On occasions when I have filled the tank brim full the tank appears to have deformed slightly and the shaft disengages from the valve, Give the shaft a waggle to re-engage it. Fully closed (clockwise) should feel like a hard stop when you twist the wheel. Fully open (anti clockwise) allows the wheel to keep turning but with a clicking, ratchet noise.

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Thanks Guys!


I did try to open the shaft mechanism via the black wheel handle but the valve movement at the bottom of the shaft was slight, only a couple of mm. When I tried to open it further, the shaft did move a little, but then repeatedly jumped back to its open position of a few mm which doesn't seem normal ?


So I tried closing it again which only took about a couple of turns. The wheel handle was then really solid so I didn't want to force it any further, especially as it appeared to shut tightly. I checked underneath and the was no escape of water at this point.


Then I started putting water into the tank (approx 15 litres) until I heard water coming out of the overflow underneath again. I then checked to see how far the water was above the black valve at the bottom of the shaft, it was about 3 cms above.


So I guess the seal at the bottom of the shaft in the tank isn't water tight and needs to be replaced.


Do these parts come separately or in a set replacement package. Any idea where I can get hold of a replacement?





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....depending on access and location, replacement could be a pig of a job.


Parts would probably have to come via a Carado dealer (though, in fact, many German 'vans also use the same valve, particularly the makes in the Hymer group). I haven't seen one, or any bits, on general sale.


Just to be sure you've tried everything on the existing one:


Mine takes approximately two turns between the fully closed position (as far clockwise as it will go), and the intermediate 20 litre overflow 'travel' position. (basically, you are supposed to open it (anticlockwise) to the 20 litre position to dump all but that amount, and then close down again, to enable travelling with only a reserve of water, thus assisting payload).


There is a significant resistance at this 20 litre point, whether going through an open (anticlockwise) or close (clockwise) manoeuvre. You do have to apply some extra force, on mine more so on closing - a constant pressure for 10 degrees or so, and it springs through.


If you turn through that resistance on opening (anticlockwise) then there is about another 4+ turns to fully open, at which point the valve innards freewheel (albeit with a "thunk" at each turn). I don't go beyond one thunk.


Closing by 4+ turns then takes you back to the 20 litre resistance, and through it (extra pressure) by 2 turns to the fully closed.


It is entirely possible that the number of turns may differ by 'van (the shape of the tank will dictate the depth of 20 litres of water) but the principle will be the same.


You are obviously correct that something might be faulty in the valve, but the symptoms you describe (with retention of a limited amount of water) could equally apply to a valve with a shorter throw than mine only being exercised in its upper part (from "fully open and freewheeling" through to the "20 litre" position), and not moving past the 20 litre resistance on closure to the fully closed position.


If it has been like this since you acquired it, it is also likely that it has been fully drained down, and left in the top part of the movement.


You will probably know yourself whether you're applying too much pressure, and I don't want to encourage you to break anything, but it might be worth trying that little bit extra once it appears to be fully closed, to see if you can get it past resistance..


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paid2travel - 2019-10-16 11:18 PM


Acquired a Carado A366 2012 ...




From a dealer or private sale?


If from a dealer then go back and ask them to show you how to operate it.


Or if from a private seller then try contacting them and asking the same question.



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....I suspected the unit might be made by Reich, and it appears that it is:




Knowing that might help with spares or replacement, but I've still been unable to locate anything on the web.


That page does, however, indicate that the one with a travel position is fully adjustable (as I said above, that was likely to enable it to cope with different tank shapes and still keep nominally 20 litres in the tank at the travel position). In that case, the number of turns between the positions may well vary from mine, and I'm still tending to you only working in the top half of the adjustment, and not getting past the resistance at the travel position when you are attempting full closing.

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OK thanks... will have another go when I get back home later today. I bought it in Germany two weeks ago from a non-dealership car garage but didn't get a detailed answer on this problem, their knowledge seemed very limited and certainly didn't understand what after-sales care was either. *-)
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....don't force it unduly (after all, there may be a problem), but to get past the intermediate (travel) position when closing mine you do have to use enough force to feel a little torsion in the operating rod before it "springs" through, and you can then do a few more turns under normal pressure to the fully closed position..
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In the end I took out the shaft and valve, stripped it down a bit, fiddled around with it and gave it some lubrication, then tested it over the sink by pouring water down the centre of the black valve cover to see if any water was still escaping through the centre section. It seemed to do the job, so I put it back in the tank and put in around 50 litres and thankfully its now holding water above its 20% level without any leaking.


But what I hadn't realise is that I have another leak going on underneath the MH at the same time ! This one is coming from the other side of the van from a short black spout directly protruding from what appears to be the floor? Its not from the waste tank so I haven't a clue why water is running out from this location?


It does seem to be slowly draining the fresh water tank though, any ideas ?




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...if it's anywhere near the water heater (probably a Combi boiler) it is most likely the Frost Control Valve for the boiler which hasn't been closed. It will empty (most of) the hot water side, and, even without the pump on, will sometimes syphon the contents of the tank.


Alternatively, Hymer Group 'vans sometimes have supplementary drain points (I have one in both the hot and cold lines) which should be opened to drain down.


Whatever, if it is coming from a spout intruding through the floor, it is odds-on an intended drain or overflow point, and is likely to have a tap/valve in the immediate vicinity inside to control it.


(my money is on the water heater frost valve).

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OK thanks Robinhood !


Will have a look for it tomorrow.


Haven't tried the heating on it yet - do I need to be cautious of the current lack fresh water in my tank at the moment before I try it out ?


Also, tried the pressure in taps today when I at last had some water to play with, Kitchen tap was good but toilet sink was slow and weak and shower and toilet flush were almost non existent, is that possibly due to air in the system or a weak pump ?


The van has been idle since around April this year so nothing has been used for ages.

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...I'm going to ask the obvious question - have you got the Carado and equipment manuals (and then conjecture that you might have, but they're in German!).


I suspect you're new to the pursuit, and have a steep learning curve that the manuals would assist with.


The Carado manual might be a problem, but we should, on the forum, be able to point you at English versions of most of the equipment, for download.


If I'm correct about the remaining leak being due to an open drain valve, then a likely cause of reduced pressure is the fact that the water system isn't reaching designed pressure (since quite a bit of it will be escaping through the drain valve). The bathroom outlets are quite often on the longest runs, so they are the ones that will suffer most (as will any hot side of the taps if the open drain plug is that for the water heater). I'd identify and fix the leak issue before worrying unduly about the pressure.


It is very likely that your 'van will have a (gas only, being German) Truma Combi boiler which provides both water and space heating. It is possible to run this "dry" but only if you correctly select the space heating setting only (not water heating).


The Combi units are fine once you understand the basics, and the controls, which can be confusing. Frankly, I wouldn't choose to run it dry in the first instance, and I'd recommend thoroughly reading up before trying anything.


Though I'm admittedly guessing at a Combi without electric, if I'm correct the instructions should be these:




(English follows the German).


It shows the controls, and the Frost Control valve which I suspect may be the source of your remaining "leak". (The control shown in this manual is the most likely one, but there are different ones and/or an additional one for a version with electric. Likewise the frost valve, there is an earlier version that looks different - I can link to manuals for these if necessary).


As a word of caution when playing with water - at this time of year you should ensure you fully drain down if you are going to leave the 'van unheated and unattended. All the water fittings are prone to frost damage, and Combi boilers are expensive pieces of kit. (We had an unexpected deep frost here only three nights ago). At the very least, open and centre the taps, drain the fresh water tank, and open the boiler's frost control valve. (If the taps are opened first (pump off) then the draining process tends to clear the water from the vulnerable taps).

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I echo Robinhood’s diagnosis that the water-leak from a "a short black spout directly protruding from what appears to be the floor” is probably coming from the valve that is intended to drain the water heater.


For a 2012 Carado motorhome it would be expected that this valve will be Truma’s FrostControl valve (photo and operating diagram attached below) and - as Robinhood mentions - if a motorhome’s water system includes a submersible water pump (as pictured in the 2nd and 3rd photos of your original posting) the fresh-water tank can drain spontaneously through the valve via siphonic action.


After you have addressed the water-leak, you’ll need to fill the water heater and bleed air from the water system.


This is the water-system ‘bleedIng’ procedure I use:


1. Ensure all water drain valves are closed.

2. Fill fresh-water tank.

3. Make sure all water outlets (taps, shower-control) are fully closed.

4. Place shower-head in deep bucket.

5. Fully open shower's hot-water control and switch on water-pump.

6. When water flows smoothly from shower head the boiler will be full.

7. Close shower's hot-water control and open shower's cold-water control, closing the latter after water flows smoothly from shower head.

8. Use a similar procedure to vent air from the other taps one by one, using bucket to avoid water splashing.



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Many thanks Robinhood and Derek for your advice and attachments !


Located the frost drain valve which was close beside the combi-boiler and very similar to the one you both described (other than mine had a red knob clearly marked 'open & close').


Filled up the fresh water tank then bled the water system as per Derek's recommendations (which worked a treat) and then fired up the combi-boiler for the first time. Worked perfectly and the water was surprisingly hot too!. The pressure was also far better then yesterday, so all-in-all, a very successful weekend and as total newbie to motorhoming, learnt a great deal into the bargain too. (lol)


Regarding the suggestion about the winter drain-down procedure etc, my fresh water tank pump comes on immediately after a tap is opened, so if I need to turn off the pump is there an isolator switch or do I just turn off the leisure battery indicator on the main control panel ?



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Sounds good.


If the frost valve is like this:



then it is the older style.


The function is similar, but the older one has (IMO) 2 advantages - it can be held shut using a peg if the weather is cold when you are filling - it also will not dump when the Combi is in use (being electrically operated). On the other hand there is a constant background current drain when it is closed. The newer one is passive and doesn't have any electrical connection.


(You understand that these provide frost protection to the boiler when their temperature falls below a given level, and generally they will not close again (manually) until the temperature is somewhat above that which is why the first two points on the older one are advantages as you can override this (with care)).


As for the pump, some 'vans have isolation, some not. Generally either a separate switch on the control panel, or one elsewhere. (Possibly in a bathroom cupboard).


If there isn't isolation, then the main 12V switch will do, BUT, I'll guarantee if you resort to this, and leave the taps open (as generally recommended) on drain down, you'll forget, turn the 12v on to use the lights, and the pump will be running away dry - not good if left for long.


So, after a short period after drain down, you may wish to close the taps!


My last van had no pump isolator, I fitted a small, neat automotive rocker in the pump circuit.

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Martin has said that his Carado motorhome is a July 2012 model, so it would be peculiar for it to be fitted with the older type of Truma safety/drain-valve that has a red ‘pull-up/push-down’ operating knob. This valve was designed to need a 12V power-supply to hold it closed and was connected electrically to a Trumatic C combination air/water heater.


However, the Trumatic C range of appliances was superseded in mid-2007 by “Combi” appliances (pictures on this link)




at which point the ‘red knob’ drain-valve was replaced by the ‘blue knob/button’ FrostControl valve that is manually operated and is not connected electrically to a “Combi” heater.


It’s possible (though unlikely) that Martin’s Carado has a Trumatic C appliance (pictures on this link)




but that would mean Carado installing a heater type in 2012 that became obsolete 5 years before.


There’s also the (remote) possibility that, between 2012 and now, someone has replaced the original heater and/or the original drain-valve, or simply that the Carado’s present drain-valve (with the red knob) is not a Truma product.


As you’ve said, there are pros and cons for each type of drain-valve, but a significant plus (for Truma) is that the manually-operated FrostControl valve can be used with all their water-heating appliances and on ALDE systems too.

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The Truma download I referenced above was for the version of the Combi I thought would be fitted in a 2012 model. I certainly found it odd that the older drain valve was fitted (which seems very likely given Martin's description), though there are various possible explanations.


So, a quick peruse of the Carado 2012 pricelist throws up an interesting discovery!


Many of the model variants are shown as being fitted with a "Truma Combi 6", but most (not all) Axxx versions including the A366 are described as being fitted with a "Truma C 6 kW".


Now, it may be a typo (though it looks deliberate), but the (possible) existence of the older drain valve leads one to believe that the (obsolescent) Tuma C heater was used in a number of models, even to that year.


Martin, if this is the case, the operation is fairly similar to the newer models (they will likely share the same controls), but the boiler/heater itself is of different design.


If it is the older design, (which looks very different) then the download here will describe it (along with the dump valve you probably have):




Edited to add:


It is not a typo, the brochure touches on the fact that the two different variants are used.

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I've attached 2 pics, one of the boiler and one of frost valve, The frost valve certainly looks like the older design as suggested but couldn't see a Truma identity marking to verify. However it was very well concealed so it might be on the other side of it.


Also couldn't see much on the boiler to identify it as a C4002 or C6002 but will try tomorrow in better light.


There is only one Truma control dial inside, so looking at the latest pdf pics, I it's definitely Trumatic 'C' not 'C EL'.


The boiler doesn't appear to have been replaced, but i'm no expert.




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