I've had my Bezzera BZ99 for a bit over three years and I've occasionally had problems with it dumping copious quantities of steam (not out the brewhead - through the release valve on the boiler). This is not a regular issue, but it is exceedingly disconcerting when it occurs. A quick bit of googling and forum searching this morning suggests to me that my pressurestat (which is probably original to the machine, which in turn was built in '96) needs to be replaced - is this the right idea? If so, what part am I looking for (I'd rather not order the wrong one - especially this week).

Wonder if the relief valve itself could be the culprit?

Might be - I've pulled it before, and nothing has seemed particularly wrong with it. Any way to tell if it needs to be replaced?

beanmuncher wrote:I've had my Bezzera BZ99 for a bit over three years and I've occasionally had problems with it dumping copious quantities of steam (not out the brewhead - through the release valve on the boiler).

Yep, it is the pressurestat.

The BZ99 has a boiler pressure gauge, doesn't it? The safety release valve should open somewhere between 1.6 and 2.0 bar. Note: There are some espresso machines without boiler pressure gauges and some DIY-type owners fashion a temporary boiler pressure gauge to confirm the pressure is exceeding normal operating range (i.e., using two hose clamps, a tire gauge, and short length of radiator hose hooked to the steam wand - needless to say, you can burn yourself!). That said, I suspect you already recognize the forcefulness of the steam is "turbocharged" compared to normal when these mishaps occur. If so, it's the pressurestat sticking shut and should be replaced.

beanmuncher wrote:A quick bit of googling and forum searching this morning suggests to me that my pressurestat (which is probably original to the machine, which in turn was built in '96) needs to be replaced - is this the right idea?

If you post an image of the pressurestat, it should not be difficult to identify (probably a CEME or MA-TER; see How to adjust an espresso machine pressurestat for photos).

Here's the pressurestat in question. I pulled it out and cracked it open - metal diaphragm and some moderate grunge/corrosion on the inside near the metal on metal seal. Scrubbed it, put it back together and tried to fire up the machine... at which point it started making the heating/hissing noises I associate with impromptu steam baths. Turned the machine off.

At a guess (from the last time the BZ99 needed major surgery), that's a 1/4" connection.

I also pulled the relief valve and had a look inside (I've pulled it several times over the last few years when this issue has come up). Flipped the plastic gasket inside (hard, white plastic held in place with a single screw) and scrubbed it but good. Machine is warming up now, just as a test.

beanmuncher wrote:At a guess (from the last time the BZ99 needed major surgery), that's a 1/4" connection.

I don't recognize the model, so I asked Jim at 1st-line about this pressurestat. He was pretty sure it's no longer made and recommended a MA-TER replacement.

Thanks Dan! The BZ99 seems to work for the moment, but I'm placing the order before I go in to the lab this morning.

Of course, what week does it choose to act up? The week I'm applying for three years of graduate funding.

Just ordered one from Great Infusions - I wanted someone who was on this side of the country (or I would have ordered from 1st-line for being a great resource). I'll post again once I've got the part in hand and have replaced it.

Thanks!

Sorry to bring this up at this time but . . . try to check the amperage ratings on the old vice the new. I'm thinking that this Bezzera machine, like its siblings, switch the heating element directly from the pstat and thus need a little meat on the contacts.