I acquired a 2nd hand VBM Domobar Super HX a while back. The boiler gauge is not accurate, Eric's thermometer tells me the Super idles at about 208-210 if left for a couple of hours while the gauge suggests the boiler is cycling between about 1.4 and 1.6bar!

I haven't paid this too much attention as I read Eric's therm anyway and I know the gauges can be quite inaccurate.

This morning the Super came on on timer, when I got into work about 2 hours later Eric's group thermometer was reading 225!

I flushed for about 10 seconds and nothing but a little steam came from the group. I opened the hot water tap and filled a cup, it didn't seem super overheated. I then switched the pump on again, water started coming from the group, I flushed plenty out and pulled the temp back to about 210. For the rest of the day it's seemed pretty normal, maybe a little on the hot side.

I've reduced the boiler pressure a bit (something I'd been meaning to do anyway).

I get the feeling the pstat is bit tired, adjusting it certainly feels a little clunky, especially compared to my VBM HX Jnr at home, which is not quite 2 years old yet.

Could this indicate my pstat is starting to fail?

Sounds like your PStat up way too high which would cause the steam and very high temp. The deadband can get bigger as you get toward the top limit of the PStat range, and it takes longer to get the group up to higher temps like that. Of course the PStat could need to be replaced but try turning it down closer to 1.1 bar first.

The pstat has had the boiler hovering around 209 degrees for several weeks, and nothing has been changed.

I already know that the machine gauge is off the mark as it reads 1.5, based on the group thermometer I'd say the top of my deadband is no more than 1.1.

To re-state, one day out of the blue an hour after coming on the group thermometer was reading 225 instead of about 208. Flicking the lever didn't cause superheated water and steam to come from the group, instead just a little bit of steam.

Emptying about 5oz from the boiler through the hot tap seems to have set things back to normal.

At the moment I suspect an intermittently faulting pstat.

Have you checked for scale build-up in the PSTAT and manometer? Sometimes you can descale the rest of the machine but scale deposits stubbornly remain in cramped passages -- or scale may have passed a threshold. Awhile back Robert Pavlis posted a recommendation to power up and down for repeated cycles with a white vinegar solution because citric acid often using in descaling can create its own precipitant.

Hi Gary, thanks for the suggestion. I have yet to de-scale the machine at all, it's something I haven't researched yet either... always wondered how much (if any) of a de-scale can be done without dismantling various bits and pieces first.

I'll see if I can track down the post you're referring to and do some reading.

Cheers.

You should be able to descale without disassembly. Just bring it to pressure and shut it off. Bring it to pressure and shut it off. I've given you the bottom line on the vinegar. Here are some tips from that thread. Use regular store bought white vinegar. Dilute it 50:50 with water. Once you're done descaling rinse the machine thoroughly with water so your espresso doesn't taste like salad.

How to descale HX espresso machine

And this has Robert's explanation about why he uses vinegar and how deposits can get stuck in pressurestats. La Pavoni Europiccola not heating

Just want to add that Robert Pavlis' descaling recommendation was for a Pavoni where the pStat tube is at the very bottom the boiler, and the pStat is below the boiler. This makes it much more prone to potential clogging by calcium citrate that might precipitate and settle during a citric acid descale. The use of vinegar avoids that. That design also makes it easier to descale the pStat and tube without removing anything. Also, it's real easy to flush and rinse a little Pavoni and get rid of the vinegar.

On your VMB HX I'd stick with citric or a vendor-recommended descaling solution. These machines are harder to rinse clean, and I don't think there is much concern about calcium citrate clogging a pStat tube, which would be located up high on the boiler with a pStat above the boiler water level.

On a big machine with the pStat and tube above the water level, it's a little trickier to descale those parts. If you think they may be scaled it might be best to pull the pStat and/or the tube to check. If necessary you can drop some hot citric solution into the open end of a removed pStat (rinse and repeat) and just give the pipe a good soak and workover with pipe cleaners.

In addition to the link that Gary provided, Stefano has a very complete how-to, specifically for descaling a Vibiemme Domobar Super: http://www.espressocare.com/PDF-Files/V ... -14-11.pdf

Andrew_NZ wrote:At the moment I suspect an intermittently faulting pstat.

Makes sense to me. My HX did something like that once and I came to the same conclusion, figured it was sticking switch contacts on my CEME pStat, which I replaced (perhaps unnecessarily.) Did not see any evidence of scale when I removed my old pStat.

Stefano also sells descaling solution he likes more than vinegar. Thanks, Pat, for your good thoughts on this.

Cheers guys, looks like I have some fun ahead of me.

I did a little reading on my sirai pressurestat, wondering if it's worth pulling the cover and checking it out.

Figure I'm looking around the platform and spring for some sort of build up. The Super was put into storage for a year or 2 and certainly needed a good clean when I got my hands on it.