Written for Gaggia owners, but applicable to all 3-way valve equipped machines;
Words to live by;
First - it's not possible to back-flush non 3-way valve equipped
machines. Trying to do will end up with detergent being forced into
the boiler. It's nearly impossible to get the detergent out of a
boiler without completely disassembling and cleaning - too much
effort, so don't try to back-flush your Carezza, Espresso, Evolution, etc!
Second - the 3-way valves in the Classic & Baby machines must be kept
clean if they are to function properly. If it's not cleaned out
(either by back-flushing with detergent or by disassembling & cleaning
it) it will eventually malfunction.
The solenoid controlled 3-way valve has *only* two purposes: 1)
Provide a leak-proof way to direct hot water from the boiler to the
group head. 2) Redirect the left-over (pressurized) coffee from the
group head to the drip pan after a shot is pulled. It's the second use
of the 3-way valve that creates problems. The residue left behind
after a shot is pulled will build up in the 3-way valve, plugging the
passageways and causing the plunger in the valve to seize.
Gaggia & Rancilio both discourage back-flushing and both will void the
warranty of any machine that's back-flushed. Their concerns has
nothing to do with machine functionality; in fact other manufactures
using identical parts in their prosumer & commercial machines
recommend regular back-flushing.
My theory is that Rancilio & Gaggia don't want noob baristas scalding
themselves with hot water & then suing the manufacturers. OK by me,
but it doesn't fit in with our forum members, who are experienced
users and know how to follow directions.
My mantra - "Keep it clean, keep it working!"
Tex