Is my expansion vessel faulty?

[Fish2306]

Hi All, Need help please. I noticed the radiators upstairs were not getting hot and the top of the towel rail in the bathroom was cold. I bled the air out of all the radiators checking downstairs too and refilling water using the filling loop as i went. I got to having 1 bar system pressure and no air in radiators. All good.

After turning on the heating the system pressure quickly reached 2.5 bar which seems high to me so I turned it off again. I checked the expansion vessel by depressing the valve and no air or water came out. I allowed the system to cool, drained it to below the level of the vessel, which is external since the original failed some years ago, and recharged the vessel to 1 bar. I then refilled the system to 1 bar bleeding the radiators as I went. Had to keep refilling and bleeding until I had 1 bar system pressure and no air in radiators.

All was good for about an hour when the system pressure began to drop and was soon at zero again, I filled it up again and it just dropped again, This went on for about 36-48 hours until now I have just over half bar pressure and it’s stable with no more loss. Problem is I now have cold radiators again in the bathroom and the expansion vessel appears empty again. Nothing, no air or water coming out when depressing the valve. I’ve checked the valve on the vessel with leak detection fluid and seems fine. I don’t understand it. When in use the system pressure rises to around 1.5 bar.

This has repeated several times now. I’ve called out plumbers and they just find the vessel is empty, do exactly what I have done above, and leave with the call out fee. They don't seem interested in finding the root cause. Within hours the pressure is dropping and it just repeats again unless I just put up with cold radiators upstairs. I’ve asked plumbers to check the vessel and they say no water coming out it must be fine. I seem to be in the situation now where the vessel is doing nothing and the upstairs radiators are full of air and in essence acting as an expansion vessel.

There must be a fault somewhere. Is it the vessel, a leak in the pipework/radiators, a combination of the two or something else entirely? I don't understand how the vessel can be good and yet loose all it's pressure within 2 days of me, or a plumber, charging it.

Apologies for the length of the question but thought it best to add detail. Any help would be appreciated.

 

[terryplumb]

If your system is constantly losing pressure ,and you keep topping up the water has to be escaping somewhere. Either a system leak ( rads / pipework), or loss via the boiler ( pressure relief valve ,PRV, or via the condensate drain). You need to sort this out before tackling the EV problem.

 

[Johntheo5]

After draining below the vessel level did you remove the outlet pipe at the vessel as that is the only way that you can be absolutely sure that there is no back pressure while recharging before refilling, no harm either to check that the piping from the EV to where its connected into the system is clear, if its a solid pipe just refill (while disconnected at the vessel end) until water comes out of the disconnected end.

 

[Fish2306]

After draining below the vessel level did you remove the outlet pipe at the vessel as that is the only way that you can be absolutely sure that there is no back pressure while recharging before refilling, no harm either to check that the piping from the EV to where its connected into the system is clear, if its a solid pipe just refill (while disconnected at the vessel end) until water comes out of the disconnected end.

Thanks for that. I hadn't considered a blockage. My plan next was to disconnect the EV, inflate it to 1 bar and leave overnight. If it's still at 1 bar in 24 hours or so then I'll assume the EV is good. I'll then check for a blockage as you suggest using the filling loop to push water through. While the EV is disconnected, the pipework capped off and everything cold, I'll re-pressurise system to 1.5 bar and again leave for 24 hours or so. If the pressure drops then I guess there is a leak somewhere I'll need to find.