240 RSF failed expansion vessel

[nishnish]

Hi,
On a 240 RSF, water comes out of expansion vessel valve when depressed.
Strangely, pressure does not jump greatly when CH is on. From 0.8 up to about 1.5. I thought a failed vessel would mean a large pressure rise up to 3bar and then PRV venting? I don't get that.
The installation manual says that the gas valve must be removed to replace the expansion vessel.
Does this mean I need an RGI out, just to perform this simple swap?
Cheers.

 

[Agile]

Its not such a simple job and does need an RGI.

You could add an external EXV to the system somewhere.

You probably have air in the top of the rads adsorbing most of the expansion so DONT go bleeding them!

Tony

 

[nishnish]

Its not such a simple job and does need an RGI.

Not simple in general, or not simple *because* it requires an RGI?
The expansion vessel seems attached by a single nut. Pretty easy to replace? Except for the gas valve being in the way.

You could add an external EXV to the system somewhere.

Could you recommend one?
I see the original one is bout £35, but I can get any if it's external to the boiler, right?

You probably have air in the top of the rads adsorbing most of the expansion so DONT go bleeding them!

I've drained and refilled it many times with little effect. My routine of one bleed pass of all rads, mustn't be removing all air. Thankfully
On old rounded top rads, the bleed nipple is a half inch or so below the rad top. Perhaps it's impossible to bleed these fully?