Machine displays AL1 and stops heating; coffee is cold or only lukewarm.

Safety first: Turn the machine OFF, unplug it, and let it cool completely before opening any panels. Hot boilers and live mains wiring can cause severe burns or electric shock.

• Power-cycle the machine: Unplug for 5 minutes, then plug back in and restart. If AL1 reappears immediately, continue below.
• Access the brew boiler sensor: Remove the top cover (usually several screws). Locate the brew boiler (smaller boiler on many Lelit dual-boiler models) and find the NTC temperature probe screwed into the boiler body with two small wires leading to the control board.
• Check the connector: Ensure the NTC probe plug is fully seated on the control board and that the wires are not pinched or broken. Reseat the connector several times to clean light oxidation.
• Inspect the probe: Look for scale buildup or leaks around the probe. If the probe is loose, gently tighten it (do not overtighten brass fittings). If the cable insulation is cracked or burnt, the probe assembly should be replaced.
• Test continuity (advanced): With a multimeter set to resistance, measure across the NTC leads (disconnected from the board). A typical Lelit NTC will show a few kΩ at room temperature. Infinite (open) or near 0 Ω (short) indicates a bad probe.
• Replace if needed: If the probe is faulty, replace it with a compatible Lelit brew boiler NTC temperature probe. If a known-good probe still triggers AL1, the main control board may be defective and should be evaluated by a technician.