I had some problems with my Vesuvius and as can happen in these situations it crept up on me and mentally I accepted it as normal a lot of the time and simply forgot how quiet and water efficient the Vesuvius was. Until I fixed it when it all starkly became obvious again!
So, whilst nor particularly technical I’ll hopefully help others who might experience the same.
What were the symptoms?
1. Increased water usage - the drip tray filling more regularly and the distant sound from another room of the Vesuvius re-filling the steam boiler when in eco mode. This is the part that crept up on me
2. Water under the drip tray no matter what I did - I even cut up and glued pieces of sponge together placing this long thin strip between the front panel and back of the drip tray. To no avail I might add. I tested the drip tray for leakage by leaving it over the sink, no problem. I had the cup tray and top panel off to observe over a day or so if water was leaking down inside the front panel. On more than one occasion. I could never see it coming from the hot water arm joint so no problem there.
3. The vacuum breaker only closing off at around 110c to 115c temperature - meaning a lot of excess steam coming from the drip tray outlet pipe and flashing up the front of the Vesuvius panel. This was what was running down but with the sponge method I couldn’t be sure, I was convinced I had blocked that from happening yet there was water under the drip tray whenever I looked.
4. Water under the Vesuvius randomly, no set pattern, sometime it did, sometimes it didn’t, something wasn’t right!
5. 
I was encouraged to investigate the vacuum breaker as it sounded (apparently) like it was not closing off before the steam boiler reached 100c temperature. So onto that next.
What did I need?
1. Small hands – I’m not joking, if like me you have large hands then reaching the black plastic vacuum breaker to unscrew it is manageable and I did so but because of the spring inside when trying to put it back together when you need two hands and you are compressing a spring this was a nightmare.
2. A crow’s foot - the much more sensible approach was to undo not the black plastic vacuum breaker so leave that compressed and instead undo the metal hexagonal piece above that which means you then have the entire vacuum breaker on the end of the ptfe tubing in your hands and it’s much easier to open and close it. To do that you need a crow’s foot to undo the hexagonal piece you can see above the vacuum breaker.
I hadn’t heard of them either but I bought this below (if you can I suggest buying an even thinner set as you don’t have a lot of room to turn it when unscrewing or screwing it up afterwards):
The 24mm in action which I found to be the right size:
3. An understanding of what happens when you do undo the black plastic vacuum breaker itself – I’m not joking. I sort of knew there was a spring inside but the jack in the box effect of pieces flying out still got the better of me.
This is what you’ll find inside with the base at the bottom (on the ptfe if you left it in situ like I did) and then the items shown from left to right sit inside the base from bottom to top:
4. A 19mm spanner just to nip up the vacuum breaker to the 24mm hexagonal part before putting it all back in
5. .PTFE as good practise when fitting that 24mm piece back to the T-section (shown in one of the earlier pictures) still on the boiler outlet pipe.
What did I check?
1. The base for debris – I was encouraged to do this in case something was fouling the spring assembly (the bottom longer spring doesn’t shut off the vacuum of course)
2. The bottom spring for damage, all looked fine
3. The top ‘memory’ spring to see if it still reacts properly to water temperature. You haven’t heard of memory springs? No. Time you looked it up on youtube then as spectacle frames are an example of this (I did and now I know) and tested the spring in cold and near boiling water to see if it still does its job (I did and here it is - the small one on the right):
Cold ie. compressed
Hot ie. expanded
4. The O’ring that seals the assembly when the memory spring expands ie black o’ring on the black part in the middle of the picture above.
I couldn’t see any issue with the O’ring but it was the culprit.
What O’ring did I use as a replacement
I was encouraged to choose something like viton that would withstands the high temperatures and the answer was thankfully in a cheap kit I bought from Amazon.
A quick visual comparison suggested either the 12×2.4 or 14×2.4 and the 12mm seemed too tight so in went the 14mmx2.4mm. Yes it was thicker and I thought that might be an issue but it wasn’t. So that choice is shown in the pic above.
What about after the repair?
Well, it’s been about a month now and all those symptoms I mentioned at the beginning are resolved. The Vesuvius is the quiet, low water—usage sophisticated machine I forgot I had. Thanks to DC as always for the pointers and teachings and as you can see it really wasn’t that hard to fix a tiny part that can cause a whole lot of trouble and cost us a lot if the coffee industry forces us to buy a new vacuum breaker.