DIAGNOSIS The ‘Hot’ setting is a post-brew heater. If your water is lukewarm, the most likely culprit is a heavily scaled-up heating element or a failing thermostat.
FIX Run a full descaling cycle. Scale acts as an insulator, preventing the heater from working efficiently. Use the Keurig descale mode with their official solution or white vinegar. Make sure you follow the on-screen instructions exactly, including the long pauses to let the solution soak. After descaling, run at least 4-5 water-only brew cycles to flush all cleaner out before making coffee.
IF THAT DIDN'T WORK Check that you’re not accidentally lowering the temperature in the app. Open the Keurig app, go to your machine’s settings, and verify the ‘Brew Temperature’ is set to ‘Hot’ (around 197°F). The app settings override the panel button.
HEADS UP If you have very hard water, you may need to descale every 3-4 months to keep performance up. Also, always use the water filter—it helps reduce scale.