Hi,

I recently re-discovered my pre-millenium pressurestatted La Pavoni Europiccola and used it several times during the last couple of days.
I noticed quite a bit of limescale build-up in the boiler so today I decided to descale it with a 30/70 vinegar/water solution.

Descaling went fine and the boiler looks clean, but I noticed that the pressure release valve now hisses whenever water in the boiler is nearing boiling temperature and the device is switched on.
In the past I never noticed any hissing from the safety valve. My device does not have a pressure gauge so I can't get any information as to the actual pressure inside the boiler.

I disassembled the valve (of the metal ball-spring type) but didn't notice any unusual wear.
After re-assembly, the problem persists: when I switch on the device, the valve starts hissing. After a while, the green light goes out, so I assume the pressurestat is working fine.
If I switch off the device, pressure drops to zero after less than 2 minutes.

Any ideas on what causes this problem and how to fix it? Or do I simply need to replace the whole valve assembly?

The trouble is a dirty or corroded metal valve ball. One can get valve lap compound and use it to resurface the ball and valve seat. However, the best solution is to purchase the extremely inexpensive mushroom shaped replacement for the ball from various La Pavoni spare part sources. Usually plastic things are inferior to metal. That is NOT the case here!!! I suspect the problem at its heart is that the ball and seat are different metals, and we are seeing dissimilar metal contact corrosion. I have examined balls with the problem with a metallurgical microscope and the ones I looked at had a rough surface. Be careful to get the correct plastic mushroom. Later machines have a differently shaped valve seat and La Pavoni attempted to put a tiny vacuum relief valve onto the pressure relief valve "Mushroom." Also the springs are different on the ones with pressurestats and on the ones without.

It is also much easier to put the pressure relief valve back together with the plastic mushroom than with the metal ball! This, unlike some La Pavoni plastic so called innovations, was a good idea!

Agree 100% with what you said. The Teflon mushroom forms a very good seal even if the valve seat is corroded. A note regarding the antivacuum valve assembly. It works perfectly fine, but it's so tiny that it's easy to cook the minuscule gaskets, especially the small o-ring. Otherwise it's a very underestimated upgrade, that is compatible and that can be retrofitted to every post 1974 EP, although it can be expensive.

Thanks for you both for the feedback. It seems that I'll have to order some replacement parts, then.

pizzigri wrote:Otherwise it's a very underestimated upgrade

What's the advantage of the anti-vacuum valve compared to the teflon mushroom?

The anti vacuum valve also results in bleeding the air from the top of the boiler during start up. It also can prevent damage to some pressure gauges. If one do not remove the portafilter after the last espresso, air rushes through the puck when the vacuum developed by the cooling of the boiler results in the handle rising. This can draw espresso back into the boiler.

However, this device does not eliminate the need to bleed air from the group, especially in 1975-2000 group models, and you still need to open the steam valve to get this accomplished. I did not install the anti vacuum valve on my either my 1978 or my 1999 model because I always remove the portafilter before disconnecting the power, and I use a pressure gauge boiler top to check pressure when I think it needs to be measured.

Ok I ordered the Teflon mushroom and a new spring, just to be sure.
The anti-vacuum valve doesn't seem like it's a necessary component since my routine is similar to yours.

An update...

I ordered the plastic mushroom thingy (part no. 371416) and the spring that goes with it (part no. 311406) but the hissing is exactly the same as before...

Any ideas? I can imagine that some hissing is normal, but it's weird to me that I never noticed any hissing before...

avh wrote:I ordered the plastic mushroom thingy (part no. 371416) and the spring that goes with it (part no. 311406) but the hissing is exactly the same as before... Any ideas? I can imagine that some hissing is normal, but it's weird to me that I never noticed any hissing before...

Machines with pressurestat should not hiss at all once warmed up. The standard safety release valve for these should be closed tight until the neighborhood of 1.5 bar.

In these cases it's possible that the pressurestat is running too high. But in your case I think you bought the wrong spring. I think #311406 is the weaker 15 coil spring that belongs in the older machines without the pStat. You want #311407 - the stronger 8 coil spring.

homeburrero wrote:But in your case I think you bought the wrong spring. I think #311406 is the weaker 15 coil spring that belongs in the older machines without the pStat. You want #311407 - the stronger 8 coil spring.

It seems you're right. I included a picture of spring 311406 with the mushroom and the metal bearing with the spring that was originally in the valve:

I switched springs and now the hissing stopped.

Thanks!