water is leaking from the bottom of my moccamaster, underneath the machine, not from the carafe.

Diagnosis

Water leaking from the base of a Technivorm Moccamaster KBGV Select typically indicates a failure in the closed-loop water system. Because this machine uses a copper boiling element (the heating element) and a separate reservoir, the leak is almost always located at one of three points: a hairline fracture in the plastic water reservoir, a perished silicone O-ring at the connection point between the tank and the copper element, or a loose tension clamp on the internal silicone tubing. To confirm the source, you must determine if the leak is a "cold leak" or a "hot leak." A cold leak occurs immediately after filling the reservoir without powering on the machine, pointing directly to a crack in the plastic tank or a loose fitting. A hot leak occurs only after the machine reaches brewing temperature, which suggests that thermal expansion is pushing water through a degraded seal or a pinhole leak in the copper tubing caused by mineral calcification and corrosion. If water is pooling specifically under the center-right side of the base, it is likely the heating element seal; if it is pooling toward the back-left, it is usually the reservoir tank.

How to Fix It

To resolve a leak in the KBGV Select, you must isolate the failure point and replace the compromised component. Follow these steps precisely:

1. Unplug the unit from the wall outlet and allow it to cool completely for 30 minutes.
2. Remove the brew basket and the glass carafe. Place the entire machine on a clean, white paper towel to pinpoint the exact drip location.
3. Fill the reservoir with 20 ounces of room-temperature water. Do not turn the machine on. Wait 10 minutes. If the towel is wet, the leak is in the reservoir or the tank-to-element seal.
4. If no leak occurs while cold, plug the machine in and run a full brew cycle. If water begins pooling now, the issue is thermal expansion affecting the copper element seals.
5. To fix a seal leak: Remove the bottom base plate by unscrewing the four Phillips-head screws located on the underside. Carefully lift the plate to expose the copper heating element.
6. Locate the silicone tubing connecting the reservoir to the copper element. Inspect the O-ring seal. If it is flattened or cracked, remove it using a needle-nose plier and replace it with a high-temperature food-grade silicone O-ring (typically 10mm internal diameter).
7. If the plastic reservoir is cracked, the entire tank assembly must be replaced. Disconnect the tubing from the copper element, unscrew the reservoir mounting bracket, and slide the old tank out. Install the replacement tank and ensure the tension clamp is tightened firmly with a small flat-head screwdriver.
8. Reassemble the base plate and run one full cycle of distilled water to ensure the seal is watertight.

If That Didn't Work

• Check for "hidden" leaks in the brew basket housing. Sometimes water overflows from the filter basket due to a clogged filter or "bloom" overflow, which runs down the internal chassis and pools at the bottom, mimicking a tank leak. Clean the brew basket assembly with a soft brush to remove coffee oils.
• Inspect the copper element for "green" oxidation or pinholes. If you use hard water without frequent descaling, calcium buildup can cause the copper to thin and eventually develop a microscopic hole. If you see a spray of steam or a steady drip coming directly from the copper pipe, the heating element assembly must be replaced entirely.
• Examine the power switch and selector dials. In rare cases, water can leak from the top reservoir and travel down the internal wiring harness, dripping out from the bottom of the machine. Use a flashlight to trace the path of the water from the top down.
• Verify the level of the machine. If the KBGV is sitting on an uneven surface or a tilted countertop, water can pool in the reservoir and overflow the internal rim, leaking into the base. Use a spirit level to ensure the machine is perfectly flat.

Heads Up

• Never use a generic waterproof sealant or silicone caulk to patch a crack in the reservoir; the heat and acidity of the coffee will cause these chemicals to leach into your drink.
• To prevent future leaks caused by copper corrosion, descale your machine every 3 months using a dedicated citric acid-based descaler.
• Avoid overfilling the reservoir beyond the "Max" line, as this increases the hydrostatic pressure on the seals and can accelerate wear on the O-rings.
• Always ensure the machine is unplugged before removing the base plate, as the heating element carries a high current and can cause severe burns or electric shock.