beerdeor Posted April 10, 2012 Report Share Posted April 10, 2012 Hi folks I have an old ravenheat combi boiler and it keeps loosing pressure only very slowly though,but absolutly no external leaks. My guess is the expansion vessel!! my question is what should the pressure be in the vessel with no pressure in the system?? any help would be very much appreciated atb Jim Quote Link to comment Share on other sites More sharing options...
lewj Posted April 10, 2012 Report Share Posted April 10, 2012 (edited) im not gas safe by the way or it could be the prv Edited April 10, 2012 by lewj Quote Link to comment Share on other sites More sharing options...
beerdeor Posted April 10, 2012 Author Report Share Posted April 10, 2012 im not gas safe by the way or it could be the prv I did think that but the outlet for it is completely bone dry atb Jim Quote Link to comment Share on other sites More sharing options...
lewj Posted April 10, 2012 Report Share Posted April 10, 2012 ah. i dont know what exactly the pressure should be in the expansion vessle but try giving it a bar or two via car tier pump see if that sorts it there is a little nipple on the top (normally) Quote Link to comment Share on other sites More sharing options...
Davva Posted April 10, 2012 Report Share Posted April 10, 2012 On the expansion vessel, there is a valve (same as the ones on your car) press it and if water comes out you know it's full up, Should have a label on it with the correct pressures, both max and pre-charged pressure - Easy to top up with a foot pump, 2bar sounds about right, otherwise replace the vessel. But first try isolating the flow/return valves under the boiler after re-pressurising, leave it for a while with the boiler turned off and it will let you know if the boiler has an internal leak through the exchanger or if it's somewhere else on the system. If the PRV (Pressure relief valve) has discharged there will be water on the wall outside or if it's faulty maybe a drip.. Obviously, you should not remove the boiler covers for further investigation, have a look on the Gas Safe website and call around a couple of engineers, ask if anyone is happy to come have have a look without a call-out charge. Good Luck. Quote Link to comment Share on other sites More sharing options...
daz2202 Posted April 10, 2012 Report Share Posted April 10, 2012 Prob the expansion vessel and yes about 2 bar will be fine, the prv is a more probable and you may also not see the water coming out as it may evaperate before you notice On the expansion vessel, there is a valve (same as the ones on your car) press it and if water comes out you know it's full up, Should have a label on it with the correct pressures, both max and pre-charged pressure - Easy to top up with a foot pump, 2bar sounds about right, otherwise replace the vessel. But first try isolating the flow/return valves under the boiler after re-pressurising, leave it for a while with the boiler turned off and it will let you know if the boiler has an internal leak through the exchanger or if it's somewhere else on the system. If the PRV (Pressure relief valve) has discharged there will be water on the wall outside or if it's faulty maybe a drip.. Obviously, you should not remove the boiler covers for further investigation, have a look on the Gas Safe website and call around a couple of engineers, ask if anyone is happy to come have have a look without a call-out charge. Good Luck. Come and have a look without charge... Not many of those engineers about. Expect around £50 for a call out including first hour Quote Link to comment Share on other sites More sharing options...
-Mongrel- Posted April 10, 2012 Report Share Posted April 10, 2012 (edited) On the expansion vessel, there is a valve (same as the ones on your car) press it and if water comes out you know it's full up... If it's water that comes out, the pressure vessel is knackered. There is a diapahragm in the vessel that separates the gas (air) charge from the system water. The Schraeder valve on the vessel is on the charge side of the diaphragm, if you get water out of the valve then the diaphragm must be compromised. Generally an internal leak will give at least some visible indication but you would need to remove some covers to properly inspect the heat exchanger etc so not a job for the unqualified really, isolating the boiler will tell you if the leak is on the boiler or system though. If you can't see the charge pressure on the vessel, a good rule of thumb is water fill pressure plus 50%, so a 1 bar fill (normal) would have you charging the vessel to 1.5 Bar. Edited April 10, 2012 by -Mongrel- Quote Link to comment Share on other sites More sharing options...
Davva Posted April 10, 2012 Report Share Posted April 10, 2012 Come and have a look without charge... Not many of those engineers about. Expect around £50 for a call out including first hour I don't charge to have a look, gets me loads of repeat business and even more recommendations. If it's water that comes out, the pressure vessel is knackered. That's what I was trying to say in a round about way... Just re-read what I wrote and it's not explained well, sorry! Quote Link to comment Share on other sites More sharing options...
Doc Holliday Posted April 11, 2012 Report Share Posted April 11, 2012 In answer to the OP, the expansion vessel air charge should be between 0.5 bar to 1.0 bar with no pressure on the water side (i.e. - drain the boiler/system down). then fill the system to a pressure of 1.2 bar. These are the optimum pressures so will be fine across a broad range of system so long as you're not running 20 radiators without adding an additional expansion vessel. A sealed system will depressurise for 3 reasons. 1 - Thre is a leak on the system. 2- The pressure relief valve is letting by. 3 - The air charge in the expansion vessel has depleted (either through a ruptured diaphragm or naturally depleted air loss). I don't charge to have a look, gets me loads of repeat business and even more recommendations. B;imey, it must be nice to be able to go to work without having to charge folk for it. It obviously costs you time & fuel plus other overheads to get to the job plus your knowledge which has taken you thus far to acrue and professional body memberships. You are either extremely generous or extremely daft, if you will excuse my bluntness. I take the approach of not doing folk favours as they have a habit of coming bacck and biting you in the rear end. If they ant my professional services on site then they pay me for them. Hats offto you though, fella. Quote Link to comment Share on other sites More sharing options...
Davva Posted April 11, 2012 Report Share Posted April 11, 2012 You are either extremely generous or extremely daft I fear the latter Quote Link to comment Share on other sites More sharing options...
Bfrog Posted April 12, 2012 Report Share Posted April 12, 2012 (edited) As its only a very slow drop in pressure I would suspect a minor leak on the heat exchanger, auto air vent or on a radiator valve. If the expansion vessel had lost all or most of it's gas charge I would expect to see a rise in pressure as the system heated up, followed by a rapid pressure drop and discharge from the PRV indicator pipe. Just my two cents. Edited April 12, 2012 by Bfrog Quote Link to comment Share on other sites More sharing options...
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