Potable expansion vessel no pressure

[Rad1o]

We have a copper hot water tank with an expansion vessel. The tank is limited to 2bar with a pressure limiting valve.
Suddenly our hot water pressure was a bit variable. I tapped the expansion vessel and instead of a half hollow sound it was all dull. Not sure why we lost the pressure...
I tried to increase the pressure in the expansion vessel, but could not get any air pressure building up in there at all. I guess this means I need a new one.

The vessel is only 2 years old.

 

[JohnD]

We have a copper hot water tank with an expansion vessel.

that's unusual. Please posts photos.

 

[Rad1o]

There is not much to see on photos. The vessel is intakt. No leak from the flange or from the valve when it is pressed.

 

[picasso]

Did you turn the water off and open a couple of hot taps before trying to repressurise the vessel ?

 

[ianmcd]

As above you need to leave a drain point open as you charge the vessel the water needs somewhere to go to

 

[Rad1o]

I had the water turned off at the inflow, taps open and even used the pressure release to drain the water. I have a service valve in line from the cylinder to the vessel. When I close off the cylinder end and try to drain the vessel, nothing leaks back. Even trying to pump at the same time does not increase the pressure inside the vessel. The service valve is intakt as when it is open to the cylinder water shoots out.

 

[picasso]

Your last post is not very clear, post up a pic if you can and what are you using to pump up the vessel?

 

[Madrab]

Are you qualified to work on unvented cylinders? If not then you shouldn't really be playing around with one of its safety devices.

Get someone in to service it.

 

[Rad1o]

I managed to get a replacement locally.
After taking the old one off I found the reason why I could not drain it. Under the weight of 18L of water it had sagged and kinked the flexi hose on the shelf underneath enough to stop it draining. Even when it was completely empty it would not pump.

The pump I have been using is a bike pump with gauge which generates up to 7bar.

The new one is connected.

 

[Rad1o]

I thought before the vessel goes to the tip I try to pressurise again.
I removed the valve with a Shrader removal tool which was fine. Then used an electric compressor. The needle quickly shot up to 8bar and the compressor was getting to the cut out. There was no air escapingat all and no pressure whatsoever inside.

 

[ianmcd]

you have to put the schraeder valve back in or the compressor wont pressurise the vessel

 

[Rad1o]

The Shrader valve was back in...

 

[ianmcd]

The Shrader valve was back in...

I removed the valve with a Shrader removal tool which was fine.