Diagnosis
The loud, vibrating, or "grinding" noise you are hearing is the Ulka vibration pump running "dry." This happens when the pump is attempting to push water through the system, but there is a pocket of air trapped in the lines—a condition known as an air lock. Because the pump is designed to move liquid, not air, it vibrates violently against the chassis of the BES500BSS, creating that characteristic loud rattling sound. This usually occurs for one of three reasons: the water tank is physically empty, the tank is not seated firmly enough to engage the intake valve, or the machine has sat idle for several weeks, allowing water to evaporate from the internal lines. To confirm this is an air lock, check if the pump noise is significantly louder than usual and if the group head remains completely dry even after several 2-second bursts of the "1 cup" button. If the pump sounds "hollow" and no water exits the group head or the steam wand, the pump is unable to prime.
How to Fix It
To resolve this, you must force the pump to prime and clear the air bubble. Follow these exact steps to reset the hydraulic flow:
- Remove the water tank and ensure it is filled to the MAX line with filtered water. Check that the rubber gasket at the bottom of the tank is clean and free of debris.
- Firmly press the tank back into the machine. You should feel a distinct "click" as the valve opens. If the tank is slightly tilted, the pump will continue to suck air.
- Ensure the portafilter is removed from the group head. You want zero resistance for the first few cycles.
- Press the "1 Cup" button. When the loud noise starts, immediately turn the steam dial (on the side of the machine) to the "Steam" position. This opens a secondary path for the water, which often breaks the air lock faster than the group head alone.
- While the pump is running and the steam dial is open, gently lift the water tank up and down 2-3 times. This creates a "pulsing" effect that can force water into the intake valve.
- Switch the steam dial back to the "Off" position and press the "1 Cup" button again. The noise should subside into a quieter hum, and water should begin flowing from the group head.
If That Didn't Work
- Perform a Full System Flush: If the air lock is stubborn, place a large bowl under the steam wand. Turn the steam dial to the "On" position and let the pump run for 30 seconds. This forces the pump to pull water through the boiler and out the wand, which is a shorter path than the group head and often clears the blockage.
- Check the Water Filter: Remove the charcoal filter holder from the bottom of the water tank. If the filter is clogged or has become too dense, it can restrict flow enough that the pump cannot prime. Try running the machine without the filter installed to see if water flows.
- Clear the Group Head Screen: Use a needle or a thin paperclip to poke through the holes of the shower screen. If coffee oils and grounds have completely blocked the screen, the pump will sound strained because it is fighting back-pressure, even if there is water in the lines.
- Reset the Power: Unplug the machine from the wall for 60 seconds to clear any electronic glitches in the pump's timing sequence, then plug it back in and attempt the priming process again.
Heads Up
- Avoid Dry Running: Never let the pump run for more than 30 seconds without water flowing. Running the pump dry for extended periods can overheat the motor and permanently damage the internal seals.
- Use Filtered Water: The BES500BSS is highly susceptible to limescale buildup in the thermoblock. Using distilled or heavily mineralized water can cause "invisible" blockages that mimic an air lock.
- Regular Descaling: If you notice the pump getting louder over several months, use a professional descaling solution. Limescale buildup increases the pressure the pump must fight, leading to more vibration and noise.
- Tank Seating: Always double-check that the tank is flush. Even a 2mm gap can allow the pump to suck air from the room instead of water from the tank.