water is leaking from the bottom of my moccamaster where the base meets the tank, not from any of the obvious joints.

Diagnosis

The leakage occurring at the junction where the water reservoir meets the chassis on a Technivorm Moccamaster KBGV Select is almost always caused by a failure in the internal silicone delivery line or a degradation of the sealing gasket at the tank's outlet port. Because the KBGV Select uses a high-temperature copper boiling element, the heat can occasionally cause the silicone tubing to soften or shift over several years of use, leading to a slow drip that collects at the lowest point of the machine—the base plate—making it appear as though the tank itself is leaking. To confirm this, dry the exterior of the machine completely with a microfiber cloth. Fill the reservoir halfway and power on the machine. Do not brew a pot; simply let the water sit. If water begins to seep from the bottom without the pump engaging, the issue is a failed tank seal. If the leak only appears once the machine starts heating and pumping water toward the boiler, the problem is a pinhole leak or a loose connection in the silicone tubing that connects the tank outlet to the heating element intake.

How to Fix It

To resolve this, you will need a Phillips #2 screwdriver and potentially a replacement silicone hose (Part #Moccamaster-Tube-S).

1. Unplug the unit from the wall outlet and allow it to cool completely for at least 30 minutes to avoid burns from the copper boiler.
2. Empty all water from the reservoir and wipe the base of the machine dry.
3. Turn the machine upside down (or tilt it significantly) and remove the four small screws securing the plastic base plate to the metal chassis. Carefully lift the plate to avoid snapping the plastic clips.
4. Locate the clear silicone tubing that runs from the bottom of the water tank to the boiler. Inspect the tubing for any "clouding" or small cracks, specifically where the tube meets the plastic nipple of the water tank.
5. If the tube has slid off or is loose, push it firmly back onto the nipple. If the tube has a pinhole leak, trim 1/2 inch off the end of the tube using a sharp utility knife to create a fresh, clean edge, then slide it back onto the connector.
6. Check the rubber O-ring/gasket at the base of the water tank. If it is pinched or cracked, gently remove it and replace it with a high-temp silicone gasket of the same diameter.
7. Reassemble the base plate, ensuring the wires are tucked away from the heating element to prevent melting.
8. Perform a "dry run" by filling the tank and running one full cycle into the pot to ensure the leak has stopped.

If That Didn't Work

• Inspect the Boiler Seal: If the leak persists, the failure may be at the boiler's intake valve rather than the tank. Check for mineral buildup (scale) around the boiler inlet; calcium deposits can create microscopic gaps in the seal, allowing water to bypass the tube and drip down the chassis. Use a 50% white vinegar solution to descale the internal lines.
• Check for Chassis Stress Fractures: Inspect the plastic housing of the water tank for hairline cracks. Over time, the plastic can warp due to heat cycles. If you find a crack, use a food-grade, high-temperature silicone sealant to plug the gap.
• Replace the Complete Tubing Set: If the silicone has become brittle throughout its length, patching it will only lead to another leak elsewhere. Replace the entire internal hose assembly from the tank to the boiler to ensure a vacuum-tight seal.
• Verify the Tank Seating: Ensure the water reservoir is seated perfectly flush against the machine. If the tank is slightly tilted, it can put lateral pressure on the silicone tube, pulling it away from the connector and causing a slow leak.

Heads Up

• Avoid Over-tightening: When replacing the base plate screws, do not over-torque them. The plastic threads in the chassis can strip easily, which will make the machine unstable.
• Scale Prevention: Hard water is the primary enemy of the KBGV Select. Use filtered water to prevent calcium buildup from compromising the seals and tubing connections.
• Heat Warning: The copper boiler remains dangerously hot for a long time after the machine is turned off. Always verify the element is cold to the touch before removing the base plate.
• Tubing Material: Never substitute the original silicone tubing with standard vinyl or PVC tubing, as these will melt when they come into contact with the boiler housing.