the descale light won’t turn off even after i ran the descaling cycle twice with vinegar.

Diagnosis

The Keurig K-Supreme Plus utilizes a volumetric counter rather than a physical mineral sensor to trigger the descale light. The machine tracks the exact number of ounces processed through the heating element; once a specific threshold is reached, the firmware triggers the "Descale" alert. The light does not "sense" if the internal tubes are clean; it only knows if the specific "Descale Mode" sequence was completed and successfully registered by the onboard logic board.

The reason your light remains on after two cycles is likely due to a "cycle interrupt." If the water reservoir ran dry during the descaling process, or if the machine was powered off prematurely before the final rinse cycle finished, the internal counter fails to reset. Furthermore, using vinegar can sometimes leave a residue that affects the flow rate, causing the machine to believe the cycle didn't finish correctly. To confirm this is a logic error and not a mechanical failure, check if the machine still brews normally; if it does, the issue is strictly a software flag that needs to be cleared.

How to Fix It

To clear the persistent descaling light and reset the internal volumetric counter on the K-Supreme Plus, follow this precise sequence:

1. Ensure the water reservoir is filled to the MAX line with fresh, filtered water and that no K-Cup is loaded in the holder.
2. Power the machine ON. Ensure it is in an idle state and not currently heating or brewing.
3. Locate the Strong and Over Ice/Hot buttons (depending on your specific sub-model variant, these are the two buttons flanking the brew size options).
4. Press and hold both the Strong and Hot buttons simultaneously. Hold them firmly for exactly 5 to 7 seconds.
5. Watch the Descale indicator light closely. It will begin to flash rapidly and then extinguish completely.
6. Release the buttons immediately once the light goes out.
7. Perform one final "Clear" brew: Select the largest cup size (12oz) and run a brew cycle with only water to flush any remaining vinegar acidity from the needles and heating chamber.

If That Didn't Work

• Perform a Hard Power Reset: Unplug the machine from the wall outlet for exactly 10 minutes. This drains the capacitors on the control board. While unplugged, press and hold the Brew button for 10 seconds to discharge remaining energy. Plug it back in and attempt the button combination again.
• The "Full Cycle" Force: If the manual reset fails, the machine may require a full, uninterrupted descaling cycle using a commercial descaling solution instead of vinegar. Vinegar is acetic acid, which is weaker than the citric or sulfamic acids found in Keurig descaling powder. Fill the reservoir with the solution, run the descaling cycle, and most importantly, run 3 full reservoirs of plain water through the machine. The counter often won't reset until it detects a specific volume of "rinse" water.
• Check for Air Locks: If the machine is struggling to pull water, it won't register the cycle as complete. Remove the water reservoir and ensure the valve at the bottom is not stuck. Gently shake the reservoir to release any trapped air bubbles that might be preventing the pump from hitting the required flow rate to trigger the reset.
• Factory Reset Sequence: If the light persists, try a full factory reset. Power off the machine, then power it on while holding the Brew button. This can sometimes clear "stuck" flags in the firmware that prevent the descale light from turning off.

Heads Up

• Avoid Vinegar Long-Term: While vinegar is a common home remedy, the acetic acid can degrade the internal rubber gaskets and seals over time. Use a dedicated citric-acid-based descaler to prolong the life of the K-Supreme Plus.
• Water Quality Matters: If you live in a hard-water area (high calcium/magnesium), the descaling light will trigger more frequently. Using a charcoal filter in the reservoir can extend the time between descale cycles.
• Don't Ignore the Light: While the light is just a reminder, ignoring it for months can lead to "slow drip" brewing or a complete failure of the heating element due to calcium carbonate buildup.
• Clear the Needle: If you notice the brew speed is slow even after descaling, use a paperclip to gently clear the exit needle at the bottom of the K-Cup holder to remove coffee ground clogs.