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Thread: How to defeat the Pesky Truma Frost Control JG that-dumps-all-your-water

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    Default How to defeat the Pesky Truma Frost Control JG that-dumps-all-your-water

    If you have a motorhome with a Truma hot water / heater combi boiler then it probably has an 'automatic water drain' valve. The theory is that if your boiler is in danger of bursting because of sub zero temperatures freezing the water in it, this device prevents that happening. What happens is that when the valve detects the temperature has dropped to 4 degrees C, the valve will open and drain the boiler, and any water that the pump tries to send to a tap. So what I want to know is HOW ON EARTH CAN THEY PROCLAIM THAT A SOOOOPER DOOOOPER MOTORHOME IS SUITABLE FOR WINTER HOLIDAYS SKI-ING? You see lots of lovely pictures of motorhomes in snow covered Alps next to happy mummies and daddies kitted out with skis, hats, gloves, boots and goggles, - and presumably no water in the motorhome? But they don't tell you that bit. Either that or they have found a ski-ing resort where the temperature is always above 5 degrees.

    The manufacturer's answer is that you can prevent the valve from opening and dumping all your water by leaving the heater on. Oh yes? and who exactly is going to pay for the gas? Why, you are of course!
    I seem to remember in MMM that someone had found this to be a problem and described it as 'we easily dealt with that problem and could then go away on our holiday'.
    So last weekend we were off to London to see the Chinese New Year celebrations. On the morning of departure I filled the fresh water tank, removed the hose and went to turn the tap off. Then I noticed all the water pouring out of a pipe under the van. I realised what was causing it so went to investigate the automatic dump valve. I was hoping it was electrical and connected to a temperature sensor somewhere, in which case I should be able to just unplug it and off we would go. Not so. It is purely mechanical. I tried switching it to the 'normal' position but it was having none of it. It knows better than I do.
    If you have more than one brain cell and are capable of knowing if the temperature is going to drop below freezing you can disable this thing and leave it working manually. You can then drain the boiler when you perceive the danger of it freezing. You take the risk, there is no blaming Truma if you do this and you leave it to freeze and burst.
    The valve is a peculiar shaped black plastic unit with a pipe in, a pipe out, and another one that goes under the floor to dump unwanted water. First you have to drain the fresh water tank - usually via another dump valve somewhere, and the boiler, which you can do via the automatic valve as it has a manual dump position. This position is where the diamond shaped blue plastic knob is at right angles to the 'in' and 'out' pipes. In line with the pipes = normal, use the water in the motorhome. At right angles to the pipes = dump the boiler water.
    Then you can separate the valve from the pipes by lifting the stainless steel U shaped pin that should be obvious when you look at it. Unscrew the valve body from the floor of the van. Take it indoors or to your garage / shed and undo the four Philips screws holding the body together. Prize the two halves of the body apart, and be careful to leave all the bits in place. It's one of those 'dismantle it too much and springs will fly everywhere' things.
    You will see a piece of sheet stainless steel which is there to clamp the thermostatic phial in place. Remove this, and remove the phial. This is about the size of a cotton reel. This phial contains a thin oil, which expands and contracts with temperature, and is what causes the valve to operate. You need to disable this expansion / contraction function, but you need to keep the empty phial. To drain the phial, just drill a very small hole in it, 1/8" will do fine though it's not critical. About an egg cup full of this thin oil will come out when you drill the hole, so don't do it on Grandma's heirloom lace table cloth (although the oil is transparent). A few sheets of kitchen roll is ideal for soaking it up.
    Having dumped the oil, replace the cotton reel phial into the valve body, and the stainless steel springy clamp, replace the other half of the body, screw it together and put it back in the motorhome where it came from. You now have a perfectly functioning manual boiler dump valve and it is up to you to remember to use it when the weather might be cold, or when you are laying up the motorhome for a few weeks.
    I suggest you do not try to separate the valve from the pipes by removing the valve complete with pipes. The pipes are very soft plastic and disturbing the pipe-to-tee-piece connections will result in leaks when you put it back together. The seal relies on a good contact between an 'O' ring and the pipe. Any scratching on the pipe at this point or sideways distortion will result in a leak.

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    Truma sell for about £35 a little heater thingy that connects from the troublesome dump-valve to the main body of the Truma unit and which is supposed to draw just enough electricity to keep the dump-valve just above the threshold where it will let everything go. I fitted one but haven't tested it in anger as it were, but I agree with you, all-year motorhoming should not be fraught with water problems. A frozen pump, pipe or valve I can cope with ... but losing all your water is seriously bad news to a wild-camper like me. I've coped with frozen up systems when in my basic T25 in Bavaria at Christmas (recommended by the way, it was excellent), one would like to think that modern kit would be more capable of dealing with all-year/all weather conditions.

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    Quote Originally Posted by mikeroch View Post
    Truma sell for about £35 a little heater thingy that connects from the troublesome dump-valve to the main body of the Truma unit and which is supposed to draw just enough electricity to keep the dump-valve just above the threshold where it will let everything go. I fitted one but haven't tested it in anger as it were, but I agree with you, all-year motorhoming should not be fraught with water problems. A frozen pump, pipe or valve I can cope with ... but losing all your water is seriously bad news to a wild-camper like me. I've coped with frozen up systems when in my basic T25 in Bavaria at Christmas (recommended by the way, it was excellent), one would like to think that modern kit would be more capable of dealing with all-year/all weather conditions.
    Sounds good, I think I need to get one of these.

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    Default Zoomable image link to gadget instructions

    Here's the little info sheet that came with my Truma dump-valve heater. The image below is just a low-res version of what you should see via the link below which itself can be zoomed to see the diagram detail. I'm still not 100% confident of how the darned thing is supposed to work and to be honest I've never properly put it to the test. The assumption that I'm working on is that when the van power supply is ON, if the temperature drops low enough to threaten the water held in the boiler, the little heater A comes alive drawing 12v power from the boiler body itself B. NOTE: If I read it aright the 10 litres of water in the boiler itself is not heated, just the dump-valve. WORRY: Does this not defeat the whole purpose of the thermostatic dump-valve? If I were to leave the van full of water with the heated dump valve active ... could not the boiler still freeze and shatter expensively (£2k ish) while the dump valve remained warm, comfy and closed?

    I think, confronted by a worryingly cold night and a boiler full of water, I'd still spend the money on gas and warm it up to 60C a) to keep it from freezing and b) to leak a bit of heat into the cabin. Sadly there is no guidance given by Truma beyond that which you see here... it's a bit mystifying but I think on balance I'd rather have the little heater than not.

    truma dump valve heater_225x240.jpg

    LINK TO ZOOMABLE HI-RES VERSION of the above

    http://tinyurl.com/y7rfjr3t

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    Dinosaurus Oldus Maximus here.
    When I wor'a lad if I didn't want my water in my caravan to freeze I would drain it at the start of the winter. So I am used to doing it and if it freezes that's my fault.
    Similarly I can buy a car that turns on its headlights when it gets dark. I know how to turn them on, I learned that in 1966. Those who don't know how to turn on headlights can buy a car that does it for them. I don't need a car that turns its lights on by itself and costs £300 to fix if it decides not to work. Those who don't know how to park can buy a car that does it by itself. Personally I passed a driving test so I don't need a car that parks itself. I know how to drain water in my camper so that's what I'll do.


    Anyhow, I just had a thought. It's winter and you have parked your camper on your drive till the spring. Surely you have turned off the gas bottle and the internal electrics? If you haven't you can reasonably expect that a tiny gas leak, unsmellable, has emptied your gas bottle, and/or the computers in your unit have drained the leisure battery because you had to leave it turned on? Does the auto-dump mechanism apparently rely on having both gas and electric to work? I don't know if they have changed the heater mechanism but mine required you to leave the gas heater on. It sounds as if they have changed it to a small 12v heater but as you say, there are many other places containing water that could freeze. To do the job properly you have to empty both water tanks, run the pump till nothing comes out the taps, then remove the shower hose, and the 'u' bends under the sinks, and then go for a drive round to swish the water as much as you can out of the pipework. I think having said that that the auto dump valve empties most of the water out of the boiler so hopefully it wouldn't be damaged. There will of course be a get-out clause in the warranty that disavows the maker of any responsibility for frost damage.
    The trouble with a hotel is that it tends to stay in one place.

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    I think it surely stands to reason that for winter storage a total drain-down / switch off has to be the policy. I suppose the funny little heater thingy may make sense if undertaking a trip in freezing cold weather but should I find myself doing so I shall certainly burn a bit of extra gas to ensure that the boiler never goes fully cold. The potential consequences are too horrific to consider.
    Last edited by mikeroch; 20-06-2017 at 06:43 PM.

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    Yes there is the logical point that if you are using the vehicle, you wouldn't want the inside temperature to drop to 5 degrees so you would have the heater on anyway. Seems to me that the actual use of the device is to dump the water if you have forgotten to do it yourself when the vehicle is in storage. However, for it to work you would have left water in the tank and the gas or electric turned on. I suppose that might happen but the owner would have to have experienced a traumatic event which prevented them from draining water and turning gas and electric off. That would be very unusual. It might be a gizmo that came about because someone thought 'Ah, this is a good marketing idea, we can make it drain itself so you are totally safe against burst boilers, Mr Customer'. I remember thinking it was a good idea when I first heard of it. It's not till later that you realise you have to leave the gas and electric turned on for it to work. (The boiler won't work without both the electric and gas turned on)
    The trouble with a hotel is that it tends to stay in one place.

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