The Ultimate BOM — what I'd actually order
If I were building another Gaggiuino tomorrow, this is the list I'd order from — part by part, with the right pick for each and roughly what it costs. It's the answer to "just tell me what to buy."
Prices are indicative (2026, EU / AliExpress-ish) — verify before you buy
Component prices move and vary by region and seller. Treat every figure here as a ballpark to budget against, not a quote. If you spot one that's badly off, tell me and I'll fix it.
Kit vs self-source — the honest trade
A Complete Kit (Peak Coffee) is one box with a ready-made harness — convenient, but you pay a premium, wait months, and get doubles plus parts you never use. A Core Kit (DIY-EFI, £204 inc) is the lean middle: board, pre-flashed screen, LV cables, sensor, PTB, SSR, thermocouple — no junk. Self-sourcing lands about the same price as the core kit but arrives faster and — the real prize — you understand every component in your machine.
Here's the trade at a glance:
| Complete Kit (Peak) | Core Kit (DIY-EFI) | À-la-carte (self-source) | |
|---|---|---|---|
| Board + pre-flashed screen | ✅ | ✅ | board ✅ · screen you flash |
| LV cables (screen / SSR / switch-panel) | ✅ | ✅ | ✋ you make them |
| HV mains harness | ✅ ready-made | ✋ you build (Ch 5) | ✋ you build |
| Pressure Tap Block (clamp-on) | ✅ | ✅ | ✋ £36 kit or parts |
| Thermocouple | ✅ (swap for C&G) | ✅ K-M4 (swap for C&G) | ✅ pick C&G ungrounded |
| SSR + STLink tool | ✅ | ✅ | ✋ source |
| 5 V power | onboard on the V4 board — no module | onboard | onboard |
| Price (control + pressure) | ~€350–470 | ~€240 | ~€250–270 |
| Wait | months | weeks | days (multi-seller) |
| Doubles / unused | many | few | none |
| You understand it | some | most | all |
This page is the self-source route. Chapter 1 covers verifying a kit if you went that way.
The board & screen — the only "must-buy-assembled" parts
The Gaggiuino PCB is a densely-populated SMD board (STM32U585 + ESP32) — you don't hand-solder it, you buy it assembled and pre-flashed. The 4.3" screen ships pre-flashed too. These are the only parts you can't cheaply self-source. Everything else on this page is à-la-carte.
| Part | Pick | ~Price | Where (direct) |
|---|---|---|---|
| Gaggiuino V4 PCB — board only | STM32U585 + ESP32, assembled + pre-flashed | £68 ex / £81.60 inc (≈ €95) | DIY-EFI bare V4 PCB |
| 4.3" HMI touchscreen | ESP32-S3, pre-flashed | £54 inc (≈ €64) pre-flashed · €30–45 AliExpress + self-flash (Ch 8) | "Gaggiuino 4.3″ Screen – GEN3" @ DIY-EFI |
You don't need a separate 5 V power supply on the V4
Mains Live + Neutral wire straight onto the V4 board — the AC-DC supply is on the PCB. There is no external 5 V brick (Mean Well / Hi-Link) to buy, which is why no kit includes one. That module only shows up in the old Blackpill "Lego" component build, where you assemble the board from discrete parts and bolt a PSU beside it. On any assembled V4 PCB — bare or in a kit — power is onboard. (You built yours: L+N to the board, no PSU module in sight — that's the tell.)
The LV cable set comes with the kit, not the bare board
DIY-EFI's V4 PCB Kit bundles a low-voltage wiring kit — screen cable, SSR cable, switch-panel cable (plus the pressure-sensor quick-connect). The standalone screen and the bare board do not. So going à-la-carte, budget to make those three LV cables yourself — trivial with JST/Dupont ends and the 0.2 mm² signal wire below, but it's the one genuine convenience the kit buys you. Note: no route gives you the HV mains harness — you build that in Ch 5 regardless.
Bare board vs core kit — do the maths for your build
DIY-EFI sells the bare board at £68 ex / £81.60 inc, or a core kit at £170 ex / £204 inc (≈ €240) bundling: the board, pre-flashed 4.3" screen, LV wiring kit, pressure sensor + quick-connect, CNC Pressure Tap Block (with fittings, PTFE pipe, O-rings, M5 screws), thermocouple K-M4, SSR 40DA, and a USB STLink tool. Bundled, that's actually a touch cheaper than buying those parts separately (bundle discount + a pre-flashed screen you'd otherwise flash yourself). So the core kit isn't the "kit full of junk" trap — that's the full Complete Kit with its ready HV harness and doubles.
What you'd still skip / upgrade even in a kit (E24, custom wiring): the HV harness (build your own — Ch 5), the scales / load cells if you won't weigh, and you'd verify the thermocouple is a genuine C&G ungrounded (below).
Board comes only from approved suppliers — DIY-EFI (UK), Peak Coffee, or the official list. espressio.shop does not sell the board — that's the 3D-printed enclosure (next section).
Walk the mod — what you'll reach for, when
You rarely buy everything at once. Doing the mod in your head, you hit each component as the build reaches it — roughly this order:
| Stage | What you're doing | What you'll need to have on hand |
|---|---|---|
| Power switch | Remove the button spring / EU restriction (Ch 4) | nothing to buy — just the mod |
| Pressure | Clamp the PTB on instead of cutting the hose (Ch 6) | PTB kit + pressure transducer |
| Wiring | Build the HV harness; wire the boiler in series (Ch 5) | spades, silicone wire, crimper, high-temp tape, SSR, AC dimmer |
| Sensing | Thermocouple into the boiler well | C&G ungrounded TC + thermal paste |
| Electronics | Mount board + screen (Ch 7) | board, screen, LV cables, printed housings |
| Firmware | Flash / first run (Ch 8, Ch 9) | STLink (or a pre-flashed board) |
That's why this list is à-la-carte: you can order in waves as the build reaches each stage, and never sit on parts you haven't gotten to.
The enclosure & mounts (print, or buy printed)
Every build needs 3D-printed housings — a PCB enclosure, the screen housing, component and SSR mounts, scales parts. Two ways to get them:
- Print them yourself (free STLs): the core set is by Loogle (a Gaggiuino maintainer): touchscreen housing + funnel-plate mount and component housing. Browse all Gaggiuino models. Print in PETG, ASA or ABS — it gets warm near the boiler, and PLA will sag.
- Buy them printed: espressio.shop is the official Gaggiuino 3D-parts supplier (Loogle's shop) — PCB enclosures ~€9, screen housings ~€13–16, plus component/SSR mounts and scales parts. Worth it if you don't have a printer or want it done right in a heat-tolerant material.
| Part | ~Price |
|---|---|
| PCB enclosure | free (print) · ~€9 (espressio) |
| Screen housing | free (print) · ~€13–16 (espressio) |
| Component / SSR mounts, scales parts | free (print) · ~€5–12 (espressio) |
Core electronics — self-source (the cheap, cheerful part)
This is the €30–50 of parts the economics talk about. Get the right ones and you sidestep the two most common build headaches (temp faults and a fried board).
For exact, current buy-links, cross-check the official Gaggiuino Bill of Materials — the maintainers keep the supplier/AliExpress links updated there (they go stale faster than this page can). The specs below let you verify what you're actually buying, and swap in the better part where the learnings say so.
| Part | Pick — and why | ~Price |
|---|---|---|
| SSR (boiler heater switch) | Genuine FOTEK SSR-40 DA, zero-cross, 40 A | €8–15 |
| AC dimmer (pump control) | RobotDyn-style 1-channel AC dimmer, 4 A / 400 V, with zero-cross detect | €5–9 |
| K-type thermocouple | C&G ungrounded, M4 head — the part the seasoned builders trust | €8–15 |
| Pressure transducer | 0–1.2 MPa, G1/4, 5 V, 0.5–4.5 V output — mounts into the PTB | €8–14 |
| Pressure Tap Block (PTB) | CNC clamp-on block + sensor fitting + PTFE pipe + red & white O-rings + M5 screws — bolts on, no hose cutting | £36 inc kit, or included in the core kit |
| Resettable thermal fuse | 185 °C, boiler safety cutout | €2–5 |
Two picks that are worth getting right
- Thermocouple: buy the C&G ungrounded probe, not the cheapest one. Every kit ships a K-M4 thermocouple, but the seasoned community advice is the specific C&G ungrounded one — PCB builds need ungrounded, and the bargain uxcell/Finglai probes are hit-or-miss (flaky QC → intermittent temp errors). If your kit's probe isn't clearly a C&G, verify it's ungrounded and swap if in doubt. (Check: no continuity between the probe body and either wire — see the FAQ.)
- SSR: "FOTEH" is a counterfeit — you want "FOTEK". A fake 40 A SSR fails at 10 A and is a fire risk. Genuine units are heavier with crisp markings.
Pressure tap: the clamp-on block, never cut the water line
The Pressure Tap Block clamps against the group-head pressure port and seals with O-rings, so you don't cut the pump-to-boiler hose. Standalone it's the DIY-EFI PTB kit (£36 inc — CNC block, sensor fitting, PTFE pipe, red + white O-rings, M5 screws); it's also in the DIY-EFI/Peak core kits. Prefer it over the older inline-T method that splices into the hose — cutting a pressurised line is irreversible and adds two more leak points. Full install: Chapter 6.
Detail on each part: SSR · pump & dimmer · thermocouple · pressure sensor · boiler & heating · PTB install → Ch 6
Connectors, wire & crimping
Going à-la-carte, this is also where you make the three LV cables the kit would have handed you — screen, SSR and switch-panel — from the signal wire below plus JST/Dupont ends.
| Part | Spec — and the learnings | ~Price |
|---|---|---|
| 6.3 mm female spades | Insulated for general AC; uninsulated high-temp for boiler terminals; a few right-angle / "flag" spades for the tight boiler-front terminals | €8–15 (assortment) |
| 4.8 mm female spades | Lamp terminals | (in assortment) |
| Ring terminals | M4 + M5, for ground wires | (in assortment) |
| Ratchet crimping tool | 0.5–2.5 mm² / AWG 20–13 — ratchet type only (Baurix Kairon set, incl. 300 spades) | €15–25 |
| Silicone wire | Mains: 1.5 mm² (blue/orange/teal/yellow). Signal: 0.2 mm² / 24 AWG (SCHDRA 6-colour) | €10–18 |
| High-temp silicone self-fusing tape | Insulate bare boiler-side terminals (≥ 155 °C) | €4–7 |
Two connector details this build taught me
- Flag (right-angle) 6.3 mm spades at the boiler front let the LV and HV wires exit in different directions instead of sticking straight out and converging — a small, real improvement in HV/LV separation. Same crimp, just angled.
- Clamp the thermocouple wires bare — no ferrules. Ferrules on solid TC wire seat poorly and cause bad readings. Cut both TC wires to the same length and clamp bare into the green terminal.
Terminal heat tiers — pick the right one for where it sits
A coffee machine is warm and it vibrates (the pump buzzes at 50 Hz), so terminal choice matters more than in dry electronics. There are three tiers, and the build needs two of them:
| Insulation | Rating | Where it belongs |
|---|---|---|
| Vinyl / PVC (standard assortment) | ~75–105 °C | general harness — pump, 3-way valve, switch, socket, lamps |
| Nylon / PA66 (straight or 90° flag) | ~105–120 °C | the upgrade for a warm, vibrating machine; PA66-housed flag terminals are automotive-grade and ideal for the tight 90° corners |
| Uninsulated brass + high-temp silicone tape/sleeve | ~200 °C+ | boiler heater terminals only |
Nylon is the 'warm machine' upgrade — not the 'touching the boiler' spec
PA66 nylon flag connectors (90°) are a genuine step up for the tight corners and general runs — heat- and abrasion-resistant, and the housing won't vibrate off. But keep all plastic-insulated terminals, even PA66, off the boiler heater posts — those run too hot for any nylon. Heater posts stay uninsulated brass + silicone. Nylon everywhere else; brass + silicone at the boiler.
Making a clean Y-split (one-in, two-out)
Where one wire feeds two destinations, you want solid, vibration-proof, and not bulky. In rough order of preference:
- Piggyback / "aftak" spades (nylon) — a female spade with a male tab on its back. Best when the split happens at a tab (switch, component): plug the piggyback on the tab, then a second female plugs onto it. Locks on mechanically, lowest bulk.
- Adhesive-lined heat-shrink butt / parallel splice — for a mid-wire Y: crimp the single feed in one end, the two branches in the other. The glue-lined shrink seals it into one solid, low-profile lump — vibration- and moisture-proof.
- Two wires in one crimp barrel — twist the two branch wires together and crimp both into one spade; compact and solid if the combined copper fills the barrel (always tug-test).
- WAGO 221 lever connector — electrically excellent and reusable, but bulky — use only where there's room (the guide uses one on Socket N).
- Ground (PE) is special: don't splice it — stack the ring terminals on one chassis bolt (a star ground). One solid mechanical point, no Y-connector at all.
Skip the Scotchlok 'T-tap' quick-splices — and solder-only joints
The IDC "T-tap" connectors (a blade that pierces the run wire's insulation) look perfect — no cutting, instant tap — but they're the wrong call here. The piercing blade is a tiny contact that corrodes and loosens under vibration and heat, it nicks the run-wire strands (capacity loss + hotspot on a mains line), and it's bulky. On a buzzing, thermally-cycling 230 V machine that's a recipe for exactly the intermittent high-resistance gremlins you're trying to avoid. Likewise solder-only splices work-harden and crack under the pump's buzz unless strain-relieved. Crimp — piggyback or adhesive heat-shrink splice — is the vibration answer.
Consumables & machine-side
| Part | Why | ~Price |
|---|---|---|
| Thermal paste (Arctic MX-4) | SSR-to-chassis heatsinking + thermocouple boiler well | €6–8 |
| PTFE tape | Seal the transducer G1/4 thread | €2 |
| OPV spring (12 bar) or flat washers | Raise OPV above your target so it never opens mid-shot | €2–8 |
| Boiler element (only if yours is dead) | Gaggia Classic 230 V ~1200 W element | €15–25 |
You do NOT need a snubber or extra caps — if you wire the boiler right
It's tempting to add 0.1 µF X2 caps / an RC snubber to fight temp interference. On a correctly-built machine you don't need them. The intermittent "Thermocouple fault detected!" that sends people down the cap/snubber rabbit hole is almost always the boiler wired in parallel instead of series on 230 V — a wiring fix, not a filtering one. (And on a stock 230 V machine the boiler ships in series — the trap is changing it. See the Chapter 5 danger callout and Troubleshooting.) Save your €2 and your evenings.
Optional modules
| Part | What it adds | ~Price |
|---|---|---|
| Dual Scale Board + load cells (2×, spares nice) | Built-in shot weighing / stop-by-weight | €10–20 |
| ToFnLED module (with loom) | Optical water-level sensor + LED ring | €10–15 · £30 @ DIY-EFI |
Both are genuinely nice, neither is required for pressure profiling. Add them once the core build works.
Tools (buy these before you start)
| Tool | Why it's non-negotiable | ~Price |
|---|---|---|
| Multimeter | Continuity + resistance — this build lives and dies on it (ground checks, ungrounded-probe test, the ~40 Ω-vs-~10 Ω boiler check) | €15–30 |
| ST-Link V2 | Wired firmware flashing / recovery — included in the DIY-EFI kit; skip if your board is pre-flashed and stays happy | €3–6 |
| Phillips PH2 + small flat screwdrivers | Panels, terminals | you have these |
| Needle-nose pliers | Removing spades cleanly | you have these |
| Heat gun or lighter | Heat-shrink on boiler connections | you have these |
| M5 Allen key | PTB clamp screws | you have these |
What it actually costs
Rounded, and honestly:
| Route | Core (control + pressure) | + harness / scales / water |
|---|---|---|
| DIY-EFI core kit — board + pre-flashed screen + LV cables + sensor + SSR + PTB + STLink, bundled | ~€240 (£204 inc) | + harness (self-build €40–60) + scales (£21.60) + water (£30) |
| À-la-carte — bare £68 board + screen + AliExpress sensor/SSR/dimmer/PTB + your own LV cables | ~€250–270 | same harness / scales / water |
| Peak Complete Kit — everything + ready HV harness + doubles | — | ~€350–470 |
So the honest picture: à-la-carte and the DIY-EFI core kit land in the same ~€240–270 ballpark for a full control-plus-pressure build. The core kit edges it on raw price (bundle discount, a pre-flashed screen, and the LV cables done for you); à-la-carte wins on control — buy only what you need, pick the C&G thermocouple, skip what you won't use, order in waves. Neither is the expensive route. That's the Peak Complete Kit (~€350–470) — you pay for the ready-made harness and get the doubles and unused cables. The blog's "€30–50" figure is just the peripheral electronics (SSR, dimmer, TC, transducer, consumables); the board is the real spend, and now it's line-itemed so you can see exactly where the money goes.
The espresso is better, the machine costs less, and you know exactly what's inside it. That was the whole point.
Shopping list in hand. Order the board + screen from one supplier, the rest from wherever's fast, and you'll have a matched, understood, no-mystery build for well under half the price of a Complete Kit.
Next: Chapter 2 — Machine Identification · or jump to the FAQ for anything unclear.