Probe (Level / Temperature)

Stainless rod or thermocouple that tells the controller how full or how hot the boiler is — fouled probes cause overfilling, dry-fires, and runaway PIDs.

Category: Boilers & Heating

Sensors that mount into the boiler to detect water level or temperature. Level probes use water's electrical conductivity to sense when refilling is needed; temperature probes (RTDs or thermistors) feed real-time data to the PID controller.

Why it matters — Probes are how the machine knows what's happening inside the boiler. A failed level probe can leave the boiler dry (damaging the heating element); a failed temperature probe causes incorrect readings and bad shots.

Good to know

Scale builds up on level probes and insulates them, which is the most common cause of intermittent autofill problems. Periodic descaling or cleaning restores function.
Temperature probes are typically PT100 (most common in commercial), thermistor (most home), or thermocouple (lever machines).