Gaggia Classic Pressurestat Mod

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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#1: Post by MustacheMax »

This is a mostly unnecessary modification, but I wanted to see what the result would be.

The Gaggia Classic is equipped with a small, simple thermostat to for temperature control during the steam cycle. Because the thermostat is installed in the aluminum boiler case it can be frustrating when trying to steam a small pitcher of milk. The lag in the thermistor heating and cooling will cause the boiler elements to shut off mid-steam. Steam output decreases while you're halfway through steaming and then you sit there holding your pitcher while you wait for the boiler to cool down and the elements to kick back on again.

The solution to this with the stock setup is to try to ride the temperature wave: Hit the steam switch and before the thermostat gets up to temp start steaming. Hopefully you catch it at just the right time that as steam is escaping and the temperature is dropping the elements stay on and continue to heat your boiler. This does work, but is kinda annoying.

My experimental solution: Install a small La Pavoni pressurestat. Here's how I did it.

Parts List:
- La Pavoni Mater XP-110 pressurestat
- 6mm OD soft copper tubing
- 1/4 BSPP Brass Nut for 6mm tubing
- Solder Nipple for 6mm copper tubing

My 2007 model year Gaggia Classic had a steam valve body that included a small molded protrusion in what I thought was an excellent location. I know that later models and the exact replacement part do not appear to have this. I don't know what year Gaggia changed the design, though it probably was inline with other model changes (the infamous 2015 model lacking the 3-way solenoid and then changed back to goodness in 2019).

I simply drilled out this protrusion with a 1/16" drill all the way through to the internal void of the steam valve body. I then used a 1/4" drill bit (slightly larger than 6mm) which if too tight should increase to 17/64". The hardest part was clamping this up without a drill press vise. Also watch out when machining brass. Because it's so soft drills and tools that are very sharp tend to catch the part quite violently. The best way to avoid this is to intentionally change the angle of the drill or blunt the edge so very slightly.

After drilling was complete I simply soldered a very short section of the 6mm tubing into the steam valve and (don't forget to put the nut on first!) then soldered the brass nipple onto the end. I figured if this didn't turn out I could easily install a 1/4" BSPP plug and call it a day.

Reassembly of the new components is a breeze. Screw the pressurestat onto the new 1/4" fitting and move the wires from the old thermostat to the pressurestat. Just watch the wire colors this is the only orientation that worked with the normally closed switch on the Mater pressurestat.

So, how does it work? Better, I think, than factory. It does introduce an issue where when the boiler is at pump pressure (9.5 bar) it is much greater than the .8-1.2 bar for steam purposes. This requires the barista to bleed pressure initially during steam heat up... Annnnd for some reason during steam heat up it seems to get pressure locked before reaching steam temp too... Best workflow is to switch to steam and open the steam valve until steam starts coming out. Then I close the steam valve and wait for the ready light to come on. After this the machine has enough steam for 2-3 lattes. Once it's up to steam temp though the boiler response is immediate and you won't run out of steam until the boiler runs out of water!


#2: Post by bean74 »

Very nice! Definitely the best way to go, if you have an older Classic.

Unfortunately, I don't think you can get that old variant of the steam valve casting anymore, everything made since 2018 lacks that unused boss which was so hand for mods like this. I got around it by tapping directly into the headspace on the boiler: