Change expansion vessel (can it be done without draining system)

[Diyisfun]

Greenstar Highflow 440, I have bought a replacement expansion vessel, is it possible to replace this without having to drain the system.
I was thinking if the motorised valves are off, & I release all the pressure, then the rads arnt on the circuit & the EV could be removed as there, but when the new EV is fitted its already pressurised so may have problem, although I could always release that pressure & re pressurise the whole system once pipe work is connected.
Just having thoughts, so don't shot me.

 

[ianmcd]

The new expansion vessel will only be pressurized with nitrogen or air, it wont have any water in, your old one however will be full of water if it has failed

 

[Diyisfun]

The new expansion vessel will only be pressurized with nitrogen or air, it wont have any water in, your old one however will be full of water if it has failed

Im aware of that hence having bought a new one.
Thanks for a bump.

 

[pete50]

I take it the "fantastic tradesman" aka plumber, didn't fit isolators either side of the expansion vessel. Anyway to be fair I have only done this on a boat but I did it without draing the system as long as you are quick and are 100% sure that everything will fit without any faffing around. Because if your not quick and everything doesn't fit then you vcould end with water everywhere.

 

[ianmcd]

Greenstar Highflow 440, I have bought a replacement expansion vessel, is it possible to replace this without having to drain the system.
I was thinking if the motorised valves are off, & I release all the pressure, then the rads arnt on the circuit & the EV could be removed as there, but when the new EV is fitted its already pressurised so may have problem, although I could always release that pressure & re pressurise the whole system once pipe work is connected.
Just having thoughts, so don't shot me.

why would you have to release the pressure ?

 

[Gasguru]

The vessel is within the boiler.
Bleed air from all the radiators...if necessary use the filling loop to raise the pressure.
Now drop the pressure to zero.
Check the pressure of the new vessel....with a typical house set it to around 0.8 bar.
Carefully crack open the vessel hose connection...there should be minimal water loss.
Swap the vessel.

 

[Diyisfun]

I take it the "fantastic tradesman" aka plumber, didn't fit isolators either side of the expansion vessel. Anyway to be fair I have only done this on a boat but I did it without draing the system as long as you are quick and are 100% sure that everything will fit without any faffing around. Because if your not quick and everything doesn't fit then you vcould end with water everywhere.

What I have read, is that there should NOT be isolation valves either side of EV.

 

[Diyisfun]

why would you have to release the pressure ?

Because I have be using the filling loop to add pressure & pumped up the EV.
Its now time to change the EV, hence my original question.

 

[Diyisfun]

The vessel is within the boiler.
Bleed air from all the radiators...if necessary use the filling loop to raise the pressure.
Now drop the pressure to zero.
Check the pressure of the new vessel....with a typical house set it to around 0.8 bar.
Carefully crack open the vessel hose connection...there should be minimal water loss.
Swap the vessel.

There is no air in the system.
Why would I need to raise pressure, then drop back to zero?
I have checked pressure on new EV its 0.75 as specified, so its ready to fit.
I am just concerned at undoing the EV and have water rushing out (although I am in a tiled area).

 

[Gasguru]

I said

"Bleed air from all the radiators...if necessary use the filling loop to raise the pressure"

ie. raise the system pressure to ensure you have bleed all the air out

 

[Diyisfun]

I said

"Bleed air from all the radiators...if necessary use the filling loop to raise the pressure"

ie. raise the system pressure to ensure you have bleed all the air out

OK got you. Thanks

 

[Diyisfun]

The answer is YES you can, that was one of the easiest jobs Ive done.
I had plenty of old towels ready, only needed one, that was used when draining the water via filling loop.
Surprised how heavy the old EV was (full of water).