Yanto Posted June 24, 2014 Share Posted June 24, 2014 The overflow from the hot water side of the boiler was dripping a couple of years ago, i recharged the "gas side" of the vessel which stopped it. Over the past 5 months it has been gradually getting worse, I've tried re-charging with no improvement, or a slight one which soon reverts to drip, drip drip! I suspect the diaphragm has ruptured so I intend to fit a new pressure vessel. However, having never fitted one before is the water side of the vessel supposed to be filled with water prior to fitting, or just fit it and fill from the mains water supply? Cheers Ian Quote Link to comment Share on other sites More sharing options...
SootySport Posted June 24, 2014 Share Posted June 24, 2014 Hope you don't leave the Fill loop open to mains water pressure constantly, this can cause over pressurisation of the system and water going out of the overflow. Quote Link to comment Share on other sites More sharing options...
Yanto Posted June 24, 2014 Author Share Posted June 24, 2014 The answer to that is yes and no! There are two pressure vessels, one for the heating loop which runs at 1.5bar and is closed off from mains pressure, this is fine. The other is the pressurised hot water side which is left open to supply pressure so the hot water is always at the same pressure as the cold water side, this vessel is pre-charged to 3.5 bar, this is the leaky one! If i'm honest i don't fully understand the plumbing logic for the system, it looks very complicated! Quote Link to comment Share on other sites More sharing options...
corsechris Posted June 24, 2014 Share Posted June 24, 2014 Sounds like a non-vented DHW setup...if so, mains comes in to a presure reducing valve, this sets the pressure in the entire DHW and the balanced cold to 3.5 BAR, the pressure vessel is VITAL as it accomodates volume changes as the water heats. Just pop a new one on. It should come pre-charged to 3.5 BAR, but check before fitting it. That way, there will be very little air in the water side of the vessel. Bear in mind you will need to drain down the DHW to some extent to remove the pressure before you swap the vessel. Should say, I'm not a plumber, but am looking into putting in a new boiler soon so have been reading up on this stuff in readiness. I like to have an idea of what's what! The pressure vessel and PRV/TRV are very important safety features - check out the Mythbusters episode where they deliberately over-pressurise one of these things. http://www.youtube.com/watch?v=68p4ngS-yME And if you ever suffer from insomnia, this site is fairly helpful..... http://www.gasapplianceguide.co.uk/Mains_Pressure_Hot_Water_Systems.htm HTH 1 Quote Link to comment Share on other sites More sharing options...
Lyonspride Posted June 24, 2014 Share Posted June 24, 2014 So its the HW side, not the CH side? Either way, I would think the only reason for a leak at the overflow is if the overall pressure is too high. Has something changed to cause an increase in pressure? Failure of a PRV? Quote Link to comment Share on other sites More sharing options...
corsechris Posted June 24, 2014 Share Posted June 24, 2014 If the vessel has failed, then normal use will tend to make the PRV let a bit out as the temp thus pressure rises, but failing PRV is also a good shout. At least it's failing safe! Ideally need to measure the pressure in the system to make sure it's stable. TBH, given the potential for problems(!), might be worth getting it checked/serviced by someone qualified to work on non-vented systems. There is a pretty thorough annual check/service routine for non-vented systems, but I wonder how many ever get done? Not having ago by the way, just wondering. Quote Link to comment Share on other sites More sharing options...
Tricky Posted June 24, 2014 Share Posted June 24, 2014 Hi Yanto, I am a heating engineer, I'll pm you my phone number, should be able to advise on best course of action. Cheers Richard. Quote Link to comment Share on other sites More sharing options...
Yanto Posted June 24, 2014 Author Share Posted June 24, 2014 So its the HW side, not the CH side? Either way, I would think the only reason for a leak at the overflow is if the overall pressure is too high. Has something changed to cause an increase in pressure? Failure of a PRV? I wasn't very good at explaining, but yes HW side, nothing changed that i'm aware of. If the vessel has failed, then normal use will tend to make the PRV let a bit out as the temp thus pressure rises, but failing PRV is also a good shout. At least it's failing safe! Ideally need to measure the pressure in the system to make sure it's stable. TBH, given the potential for problems(!), might be worth getting it checked/serviced by someone qualified to work on non-vented systems. There is a pretty thorough annual check/service routine for non-vented systems, but I wonder how many ever get done? Not having ago by the way, just wondering. As top bloke Tricky also suggested (phone a friend) it could be the PRV and or the diaphragm, i think i will change both. Servicing was never discussed at hand over time for the system as it is pretty much sealed for life heat exchanger, with no maintenance safety items to be checked, it is a ground source heat pump, so effectively a freezer in reverse, it's just these additional bits that are liable, and obviously have become unreliable. 1 Quote Link to comment Share on other sites More sharing options...
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