So something strange has been happening the last couple of days... I turn my Rocket Giotto Evo on.. give it like 30 mins to warm up... lock and rock, pulling a very tasty 2oz espresso. The problem comes in when I begin frothing the milk for a latte or capp... while I am steaming the milk (about half way through the process..) the pump kicks on and the pressure instantly drops... the steam is then very light and begins to build back up... takes 15 seconds or so to build back up to full pressure. This is all happening WHILE I am steaming.

Anyone have any idea why this might be happening? Happening to anyone else?

Reminds me of the days I had my espresso machine on a timer. The kitchen wasn't far from our bedroom and I'd startle at the brrr-r-r! of the pump topping off the boiler some mornings.

In your case, this happens when the water level is just above the probe before steaming. If you're turning your machine off each day, try opening the water tap until the pump kicks on, let the boiler refill, then turn the machine off. The boiler level will be well above the probe when it warms up the next day. If the pump is kicking on mid-shot/mid-steam, the same trick will work.

Awesome, thanks man for the help.

IMO, even with a vac break, you should purge the boiler before steaming. Doing so removes the last remnants of false pressure and warms the wand to reduce condensation thus producing dryer steam.

Yup, pumps kicks in to top off the boiler, steam pressure drops and mucks up your micro foam. Happened to me one or twice on my Cellini Evo.

Your machine is fine. Just make sure the boiler is topped off before you steam

+1 on drawing some water from the hot water tap before turning off the machine. I jumped 3 feet off the bed the first time the pump turned on at 5h30 am

Thanks Ian, good reminder. To be clear, what I suggested was forcing the pump to top off the boiler by drawing water from the tap; this prevents the pump from later kicking in at an inopportune moment.

SOP :

Bleed steam
Warm latte / cappa cup from hot water tap
Boiler fills & heats during shot prep to a full head of steam
Pull shot & steam milk contemporaneously

To satisfy my own curiosity, can some one enlighten me on the mechanics of this loss in steam pressure? I'm not familiar with either a Rocket Giotto Evo or a Callini Evo, but to add water to a boiler you've got to have it at higher pressure than the boiler is at to get the water to go in the direction you'd like. Is this the same pump that's providing the pressure to pull shots? It's obvious that you'd lose shot pressure if the boiler-fill kicks in during a shot on a single-supply, single-pump system (exposing high-pressure shot to low-pressure boiler), but where's the pressure loss coming from during steaming only? Is the valve opening before the pump gets up to pressure, or pump shutting down before valve closes? Or isn't there any valve, etc.?
-Ed
("Looking for the candied apples on the tree of knowledge." -Greg Herriges)

decaf_Ed wrote:Is this the same pump that's providing the pressure to pull shots?

That's correct, the pump serves both purposes. A solenoid controls filling the boiler. I searched this site using "hydraulics diagram" and found this example:


Pump = part #2, refill solenoid = part #3; excerpted from Nuova Simonelli Oscar product page

Ideally, the controller would be programmed to delay refilling the boiler for 20-30 seconds if brewing was in progress, but that hasn't been my experience. You're right that for a vibratory pump, the brew pressure drops if an auto-fill kicks in mid-shot. If you prewarm the cups as Ian suggests, it will never happen. If you forget, it may happen... oh I don't know... once in 20 or 30 shots, depending on how often you steam.

I might be wrong but as the autofill kicks in, it introduces cold (or lukewarm if you are pourover) water in the boiler which will affect the head of steam. The heater will turn on shortly and bring you back up to full pressure but it's enough to ruin a milk steaming session.