Expansion vessel problem

[Corazones]

I tried bleeding my towel radiator, which is the highest point on my c/h system. Lots of air came out, so I assume that was the wrong thing to do - maybe it runs from the hot water circuit. Then I noticed that the Zilmet 4 bar expansion vessel was reading zero most of the time, and only occasionally up to 0.25 bar, so I assume that's where all the air came from. Or it could be from when I tried turning a spring-loaded valve in the system? I have read that re-pressurising through the Schrader valve isn't as simple as you might think, and involves isolating the boiler, unpressurising the whole system etc first. Is that really necessary - why can't I just pump it up a bit without doing anything else - anything must be better than what I have at the moment!
Thanks, Alec.

 

[PrenticeBoyofDerry]

No it needs to be isolated and de-pressurized to re-charge expansion vessel.
Cannot re-charge under pressure.

http://www.youtube.com/watch?v=KeO2gswQQe4&noredirect=1

 

[ianmcd]

The air that came out of your towel rail has nothing to do with the air in the expansion vessel the two should never meet unless the expansion vessel diaphragm/bladder has punctured

 

[CBF]

you need to top up your system using the filling loop, just because the pressure gauge is by your EV the gauge shows the pressure in the heating system not the EV pressure, the pressure should be around 1.0 bar when the boiler or pump aren't working

 

[Corazones]

Thank you, Ian and CBF.

Ian: I understand what you say, but the expansion vessel was holding pressure perfectly before I started bleeding air. Also it's only 3 years old, not an old installation.

CBF: I have already topped up via the filling loop, and there is a separate pressure gauge which shows the correct 1 bar on the central heating system. The gauge I am writing about is close to a flexible hose coming off the bottom of the expansion vessel, which is in the airing cupboard upstairs and connected to the hot water cylinder. It's not a combi boiler but a more complicated system which, frankly, I don't fully understand.

 

[ianmcd]

Could you post some pictures please, your description is a bit confusing , it sounds like you may have a sealed system with an external expansion vessel and an unvented Hot water cylinder with another expansion vessel (not unusual)

 

[CBF]

then the gauge will be showing the system or incoming supply pressure it WON'T be showing the EV pressure, you can only test the pressure in the EV via the valve on it & this can only be done with no pressure in the system

 

[Corazones]

Could you post some pictures please, your description is a bit confusing , it sounds like you may have a sealed system with an external expansion vessel and an unvented Hot water cylinder with another expansion vessel (not unusual)

That sounds as if you could be right. I have created an album (I haven't done this before) and am hopefully adding a photo which may help explain things better.
//media.diynot.com/11000_10318_55294_33502072_thumb.jpg

Many thanks,
Alec

 

[ianmcd]

As CBF correctly said you cant tell the pressure of the EV from the guage you need to connect a foot pump with a guage or a guage to the schraeder valve on the top of the expansion vessel with no pressure in the system, its hard to tell as your pic is so small but I would say that guage is your system pressure and that is why it dropped when you released air from the towel rail that is normal, personally I dont think you have a problem with your EV just re-pressurise your system to 1-1.5 Bar and see if everything works OK and remember that any time you bleed a radiator or a towel rail then you must top up the pressure afterwards