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Chapter 9 — First Run & Calibration

Chapter 9 of 10  ·  ~60 minutes  ·  First power-on

Read this chapter fully before powering on

The first power-on after a build is the most important moment. Things to look for, things to listen for, and things to immediately do if something is wrong are all in this chapter. Read it first.

Before powering on — final physical check

  • Machine is fully reassembled (top panel on, all screws in)
  • Water tank is filled and seated
  • Drip tray is in place
  • No tools or loose components inside the machine
  • All harness connectors are seated
  • No wires visible that could contact the top panel when replaced
  • Pressure sensor cable is connected and routed
  • Thermocouple cable is connected

STEP 1 — Initial power-on

  1. Plug the machine into the wall.
  2. The machine should NOT power on automatically — the switch must be pressed.
  3. Press the power switch. Hold it for 1 second — then release.

Expected: The switch latches in the on position (your Chapter 4 spring mod). The HMI screen lights up and shows the Gaggiuino boot screen within 3–5 seconds.

If the switch springs back immediately, the spring mod from Chapter 4 did not work. Unplug the machine and revisit Chapter 4.

STEP 2 — Observe the boot sequence

Watch the HMI screen through the boot sequence:

  1. Gaggiuino logo splash screen
  2. System initialisation messages (brief — 2–3 seconds)
  3. Home screen appears

Expected home screen shows: - Temperature display (will show room temperature initially, rising as machine warms) - Pressure display (should read 0 bar — machine is not running) - Shot timer at 00:00 - Status bar at top with Wi-Fi/Bluetooth icons

Gaggiuino HMI first boot — profile selection screen showing IUIUIU Classic, Filter 2.1, Zer0, Blooming, Londinium, Adaptive profiles. Flush and Descale buttons visible. This is the normal home screen after boot.

If the screen shows no readings or the temperature reads abnormally (far above room temperature, or a fixed suspicious number), stop and check the thermocouple connection.

STEP 3 — Verify temperature sensor

Watch the temperature reading for 2 minutes as the boiler begins to heat.

Expected: Temperature rises steadily from room temperature toward target (default 93°C). The rate of rise should be smooth — approximately 3–5°C per minute on a cold start.

Not expected: - Temperature stuck at a fixed number (thermocouple disconnected or incorrect polarity) - Temperature jumping wildly (bad thermocouple connection or electromagnetic interference from AC/DC cable routing) - Temperature showing -200°C or similar error value (thermocouple open circuit)

If readings are abnormal: power off, unplug, and recheck the thermocouple connector at both ends (PCB and probe).

STEP 4 — Verify pressure sensor

Trigger a brief pump run by pressing the brew button for 1–2 seconds (machine must be at temperature first — or use the manual pump test in Settings).

Expected: Pressure display shows a reading above 0 bar when the pump runs. With no portafilter and no coffee (open circuit), pressure will likely be low (1–3 bar). This confirms the sensor is reading.

Not expected: - Pressure stays at 0 bar while pump runs (sensor disconnected or wires swapped) - Pressure immediately reads maximum (12 bar) with pump off (short circuit on sensor)

STEP 5 — OPV pressure calibration

With the machine at full temperature, run a blank shot (portafilter with no coffee, blind basket) and observe the pressure.

Expected for EU machines: Pressure should reach 10–12 bar with a blocked basket. EU machines are factory-set in this range — verify, but adjustment is usually not needed.

US machines: The OPV is factory-set to 9 bar. Gaggiuino needs 10+ bar to profile correctly. Adjustment is required.

Where the OPV is

The OPV (Over-Pressure Valve) is a small brass spring-loaded valve located on the right side of the machine interior, between the pump and the boiler. It has a hex-head adjustment point accessible from the top of the machine with the top panel removed.

On the E24, the OPV looks like a small cylindrical brass component with a spring inside it and a bypass hose port. The bypass hose routes excess pressure back to the water tank.

How to adjust (US machines — or any machine below 10 bar)

Option A — Add M3 washers (no tools needed beyond pliers)

  1. Unplug the machine from the wall.
  2. Remove the top panel (done in Chapter 3).
  3. Locate the OPV — brass cylindrical body with a spring visible inside.
  4. Unscrew the OPV cap (the hex or slotted top) with a spanner or screwdriver.
  5. Place one M3 washer on top of the spring inside the OPV body.
  6. Replace the cap.
  7. Reassemble, power on, and run a blank shot to re-test pressure.
  8. Repeat: add one washer at a time until pressure reaches 10–11 bar with a blocked basket.

Option B — Replace the OPV spring (permanent, preferred)

A 12-bar OPV spring is available from the Gaggiuino community and third-party suppliers. Drop-in replacement for the stock 9-bar spring. Eliminates the washer stack and is more consistent.

Target: 10–11 bar, not 12

Higher is not better. 10–11 bar gives Gaggiuino enough headroom to profile without excessive stress on seals and connectors. 12 bar is the common spring spec; most builders use it as-is or add one washer if it sits high.

STEP 6 — Scales calibration (Complete Kit)

If you installed the scales in Chapter 7:

  1. Go to Settings → Scales → Calibration
  2. Follow the on-screen prompts — you'll need a known weight (100g calibration weight, or a known object like a coin)
  3. Tare, place weight, confirm

STEP 7 — Temperature offset calibration

The thermocouple measures boiler temperature, but what you care about is group head temperature. There is typically a 5–10°C difference.

  1. Use a calibrated thermometer at the group head (a puck thermometer or similar)
  2. Compare against the Gaggiuino temperature reading
  3. In Settings → Temperature → Offset, enter the correction value

STEP 8 — Pull your first calibration shot

Set a simple flat 9-bar profile (no pre-infusion, 9 bar throughout) and pull your first shot with coffee. Observe:

  • Shot pressure holds steady at 9 bar
  • Temperature remains stable during the shot
  • The pressure graph on the HMI shows the profile

If this looks correct: your build is complete.

Build complete

You did it. Your Gaggia Classic Pro E24 now has professional pressure profiling, temperature stability, and a touchscreen interface. Go make coffee.

If something isn't working as expected, go to Chapter 10 — Troubleshooting.

What to explore next

  • Profiles: The Gaggiuino community shares profiles on the Discord. The default profile is a good start; most people eventually dial in their own.
  • Web interface: Connect to your Wi-Fi and navigate to the Gaggiuino web UI from your phone or browser.
  • Bluetooth scales: If you have a Bluetooth scale (Acaia, Bookoo, etc.) enable it in Settings → Scales.