Problem 6 - The dispensing pressure is incorrect.
Solution 1 - Adjust the external boost pump.
1. Locate the adjustment screw on the side of the pump. Load
a portafilter with coffee and insert it into a group head. Press
the manual dispense switch and notice the brewing pressure
on the lower portion of the gauge. Using a flat-tip screwdriver,
turn the screw clockwise to increase brewing pressure. Turn
counter-clockwise to decrease brewing pressure.
The water pressure required to properly brew espresso is 9 bar. Most municipalities supply
water between 3-5 bar. Most espresso machines incorporate a boost pump to increase the in-
coming water pressure to the required 9 bar to properly brew. If the dispensing pressure portion
of the gauge is not a 9 bar while brewing, adjust the pump pressure.
Problem 7 - The machine makes a high-pitch squealing noise
while brewing.
The La Marzocco uses an expansion valve to bleed off excessive pressure from the coffee
boiler. The expansion valve should be set to relieve pressure at 12 bar. If the expansion valve is
set too low and the pump pressure is too high, water will discharge through the expansion valve,
making a squealing noise.
Solution 1 - Adjust the pump and/or expansion valve.
1. Ensure the dispensing
pressure is set to 9 bar while
brewing.
2. Activate one of the group heads and allow water to exit
the group until the red heating element indicator light illumi-
nates. While the light is illuminated the dispensing pressure
portion of the gauge should start to climb. Adjust the expan-
sion valve so that it starts to releive pressure at 12 bar. Turn
the expansion valve barrel clockwise to increase pressure
and turn counter-clockwise to decrease pressure.
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