Orkney1 Posted September 4, 2020 Share Posted September 4, 2020 After reading what seems like thousands of forums, I need a straightforward response to what the light grey/off-white t piece outlet valve does and if I blocked the clear hose existing the van would this cause untold damage to the unit? I can’t figure out if it is a pressure relief valve, or lets air into the unit to assist when emptying. Water is escaping us this tube but when I block this hose pressure returns and I have water again. I’m just not sure about if blocking this is a sensible temporary fix. I have determined that it is knackered but don’t reckon I will get a new part home before leaving for my travels on Monday - one is on order. Other forums state that there maybe issues with installing this new part as it is different to the one I need to replace but that’s for another day. To clarify I do not mean the auto frost protection valve, which is working fine. Pic of the valve I am talking about: https://www.wohnmobilforum.de/bilderdienst/wohnmobile/Eingebaut_94848_1d05.jpg Link to comment Share on other sites More sharing options...
hallii Posted September 4, 2020 Share Posted September 4, 2020 First let me say I have no idea. Now, putting my retired engineers hat on, could it be a one way valve, allows water out at a certain pressure but closes under vacuum as when pump starts up? If you took it off you could test it to see? H Link to comment Share on other sites More sharing options...
Gman Posted September 4, 2020 Share Posted September 4, 2020 hello, could be this part your looking for. hope this helps. https://www.ebay.co.uk/itm/GENUINE-Truma-Combi-Ultrastore-Water-Heater-Elbow-Valve-834151/283988408189?epid=1995559561&hash=item421f07377d:g:sYoAAOSw~Nta5y2R Steve. Link to comment Share on other sites More sharing options...
Keithl Posted September 4, 2020 Share Posted September 4, 2020 I believe it is a pressure relief valve and under no circumstances should you block the hose. You could try removing it and cleaning it as it may be partially jammed open by some debris or limescale. Otherwise you will have to wait for your replacement to arrive. Keith. Link to comment Share on other sites More sharing options...
Robinhood Posted September 4, 2020 Share Posted September 4, 2020 I believe that is an "aeration/breather vent" which allows air out until the boiler body is full of water, and this water then forces the vent to close. It would presumably also assist in emptying the boiler through a lower drain point by allowing air in as the water level drops. With it blocked, there is a strong possibility that the boiler will not fill to the top with water (especially if it has been drained), though you might get away with blocking it once it is emitting a steady stream of water (i.e. the boiler is then full) and ensuring that the inlet supply is subsequently not depleted/interrupted. I'm not entirely sure I'd like to take the chance, though. ;-) (I think I'd take a chance at removing the clear piping and having either a good suck, or a little poke around inside to see if something had stuck). Link to comment Share on other sites More sharing options...
Keithl Posted September 4, 2020 Share Posted September 4, 2020 Confirmed that it is also a PRESSURE RELIEF VALVE... "it’s secondary job is a pressure relief valve that in event of over pressure is to allow water out." https://www.leisureshopdirect.com/electric/caravan-gas-water-heater/truma-combi-4-6-l.p.-gas-and-electric-heater-spare-parts/elbow-fitting-for-hot-water-outlet-truma-boilers Keith. Link to comment Share on other sites More sharing options...
Orkney1 Posted September 4, 2020 Author Share Posted September 4, 2020 Thanks all, very much appreciate all you rapid responses. My better half is on full meltdown mode over this as we are booked to leave on Monday morning sailing. I have taken the valve off and the spring and ball gubbins are not there, I assume completely perished and now lost somewhere in the system, likely another problem that will raise its head once this is resolved. I have ordered the part but it will be a miracle if it arrives tomorrow, even with 24 hour express delivery. That’s why I was looking for a temporary fix. Link to comment Share on other sites More sharing options...
Keithl Posted September 4, 2020 Share Posted September 4, 2020 Try phoning round local caravan dealers or mobile caravan repair engineers to see if anyone has one in stock that you can go and collect. I believe it is a common part on many models of Truma water heater so you may be lucky. Keith. Link to comment Share on other sites More sharing options...
Orkney1 Posted September 4, 2020 Author Share Posted September 4, 2020 Cheers Keith, quick google search and there is a mobile repair fella in the highlands that I will contact tomorrow. I knew this would be helpful. Link to comment Share on other sites More sharing options...
Robinhood Posted September 4, 2020 Share Posted September 4, 2020 Keithl - 2020-09-04 8:51 PM Confirmed that it is also a PRESSURE RELIEF VALVE... Keith. I'm not entirely convinced of that. For the latest series of Combis, the Frost Control drain provides an overpressure vent at 4.5 bar (documented by Truma). I believe, but am not going to chase up, that the previous design of frost valve was similar in function. Truma's installation instructions mention it being a breather valve (only), and from their wording, I'm inclined to believe it has that function only (though patently, increased pressure in the system might cause the thing to leak if it is faulty, I don't think pressure relief is its design purpose). Link to comment Share on other sites More sharing options...
colin Posted September 4, 2020 Share Posted September 4, 2020 If it comes to the worst case which would be no part arrives, then maybe you need to assess if you need the hot water working, if not you could block the outlet to allow water through the taps, but this might also mean you might not want to use the space heater as that also tends to heat up the water a bit, but not sure if it would heat water enough to cause a problem? Link to comment Share on other sites More sharing options...
Derek Uzzell Posted September 5, 2020 Share Posted September 5, 2020 Robinhood - 2020-09-04 9:24 PM Keithl - 2020-09-04 8:51 PM Confirmed that it is also a PRESSURE RELIEF VALVE... Keith. I'm not entirely convinced of that. For the latest series of Combis, the Frost Control drain provides an overpressure vent at 4.5 bar (documented by Truma). I believe, but am not going to chase up, that the previous design of frost valve was similar in function. Truma's installation instructions mention it being a breather valve (only), and from their wording, I'm inclined to believe it has that function only (though patently, increased pressure in the system might cause the thing to leak if it is faulty, I don't think pressure relief is its design purpose). Robinhood is correct - the elbow fitting is just a ‘breather’, allowing air to escape from the boiler when the boiler is being filled with water and allowing air to enter the boiler when the boiler is being drained of water. The elbow has no 'protective pressure relief’ purpose - though it is commonly (and incorrectly) believed it has. It’s also occasionally (and wrongly) suggested that the elbow fitting provides an ‘overflow’ function. https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Water-pipe-plan-for-Hymer-694/15452/ Truma has always provided over-pressure protection via thir own specialised drain-valve. This valve could be the manually-operated type (1st image below), or a (now-superseded) electric valve for Trumatic C appliances (2nd image) or the current “Frost Control” valve (3rd image). The elbow breather should close when there is sufficient air pressure in the boiler to cause this to happen (eg. when compressed air is used to assist draining down of the motorhome’s water system). Blocking the elbow breather should be OK as a temporary measure. If a hot tap is left open when the water system is being filled, this will allow the boiler to fill up. Similarly, when the water system is to be drained down, if a hot tap is first opened this will allow the boiler to empty. (The disappearance of the breather’s innards has been mentioned on this forum before - it’s a mystery where the innards go... ;-) ) Link to comment Share on other sites More sharing options...
Orkney1 Posted September 6, 2020 Author Share Posted September 6, 2020 I spoke with a motorhome repair engineer and he confirmed that the outlet valve is not a pressure relieve valve, rather an air inlet valve to assist in draining the heater. He said that blocking the valve would cause no problems and stated that he regularly did this when attending repair jobs. Luckily the part arrived and fitted with no modification required. Thanks all for your input. Link to comment Share on other sites More sharing options...
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