Option 1: Thermostat + Float Switch Logic (No PCB)

Excellent — this is exactly the kind of smart DIY logic you can build without a circuit board, using basic electro-mechanical controls and the kettle-style thermostat principle we discussed earlier.

Let’s walk through how you can replace the water probe + control board with a simple relay logic circuit:

🔧 Goal:

When you switch on the espresso machine:

1. The pump fills the boiler with water.
2. When the boiler is full (sensed mechanically or thermally), the pump stops.
3. Then heating starts until the thermostat (temperature control) cuts off.

🧩 Option 1: Thermostat + Float Switch Logic (No PCB)

Components:

• Float switch (in boiler)
• Relay (DPDT or SPDT)
• Heating element
• Pump
• Thermostat (bi-metal or adjustable type)

How it works:

1. Switch ON → Power goes to pump and float switch circuit.
2. Boiler fills → Float rises → opens circuit → relay cuts power to pump.
3. Relay switches power to heating element through the thermostat.
4. Thermostat controls temperature (on/off cycling).
5. When water level drops (float falls) → relay switches back → pump refills → heating pauses until water full again.

Simple wiring logic:

 Mains → ON Switch → Relay Coil → Float Switch (Normally Closed)
 
Relay Contacts:
   - COM → Live Supply
   - NC → Pump
   - NO → Heater (through Thermostat)

💡 Meaning: When the float is low, the relay coil is energized, keeping the pump ON.
When the water level rises, the float opens, de-energizing the relay → pump OFF, heater ON.

🧩 Option 2: Thermostat Sensor Logic (Kettle Style, No Float)

If you don’t want a float switch:

• Use a bi-metal thermal switch attached to the top of the boiler.
• When there’s no water, it heats too quickly → switch opens → stops heater and pump.
• When water present, temperature rises slower, allowing heater to work normally.

This mimics a kettle’s dry-boil protection, where the heater cuts off if the plate overheats (indicating no water contact).

⚡ Optional Enhancement:

Add a delay relay (time-based) if you want:

• Pump runs for 10–15 seconds on startup
• Then heater activates This gives a safety buffer for water filling before heating begins.

🧠 Summary Logic (No PCB, All Electromechanical):